Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
requirements similar to dfsdm needs:
https://www.kernel.org/doc/Documentation/devicetree/bindings/iio/adc/renesas%2Crcar-gyroadc.yaml
rcar-gyroadc driver main characterisitics:
- the parent device (gyroadc) is a consumer of sub devices (SPI ADCs)
- the channels are populated from the sub devices
- the iio device is associated to the parent device
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
What is the the preferred approach for you ?
Thanks for your feedback
Best regards
Olivier
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
quoted
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
I'd forgotten about this one, so apologies if it takes me a bit of time to
get back up to speed!
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
Not a gyroscope driver despite the name :) I was thinking more of the
case where we have a gyroscope that can be wired up to a bunch of different
ADCs.
I wouldn't necessarily take that as a golden example. We were still figuring
out how this stuff would fit together.
From what I recall (and it's been a few years) that device provides no
configuration type interfaces for the SPI ADCs - they end up having no
existence in the device model as a result. There is no means of
sharing anything between the ways this device uses the SPI ADCs and the
way any other device does.
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
Good point, there isn't a means of combining the scans from multiple
IIO devices and that is what we end up having in this model.
You can 'split' the channels so that enabling sd0 and sd1 buffered
mode will result in scans from the filter filling FIFOs for each of them
but that may not fit the use model you have in mind.
This sort of demux is more often done for when we have a consumer in
the form of say a touchscreen that uses a couple of channels off a
general purpose ADC. We have no reason to want to ensure any alignment
between the data going to the touchscreen and that going to the
who ever is interested in the other ADC channels.
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
That is indeed the key question. Do we need to configure the modulator
devices? If we do then they need to have an existence in the device model.
Mapping them as IIO devices provides reusability across multiple
filter implementations.
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
That may be an option. It was always on the list of things to do
to allow for IIO devices that have no 'IIO interface' to userspace.
The main usecase was SoC ADCs where all the channels are going to
other in kernel consumers, but it might be applicable here as well.
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
Yes.
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
That one is a rather odd case because no generic handling is possible
of the ADCs. For example it doesn't use the ad7476 driver because we can't
talk to the device even though it's the same ADC as the ad7476 driver supports.
What is the the preferred approach for you ?
I still favour solution 2, but if you need to have the channels cleanly
presented in a scan despite them coming from different modulators, then that
solution may not be sufficient and we need to think about how else to do
things.
Jonathan
Thanks for your feedback
Best regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
quoted
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
I'd forgotten about this one, so apologies if it takes me a bit of time to
get back up to speed!
quoted
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
Not a gyroscope driver despite the name :) I was thinking more of the
case where we have a gyroscope that can be wired up to a bunch of different
ADCs.
I wouldn't necessarily take that as a golden example. We were still figuring
out how this stuff would fit together.
From what I recall (and it's been a few years) that device provides no
configuration type interfaces for the SPI ADCs - they end up having no
existence in the device model as a result. There is no means of
sharing anything between the ways this device uses the SPI ADCs and the
way any other device does.
quoted
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
Good point, there isn't a means of combining the scans from multiple
IIO devices and that is what we end up having in this model.
You can 'split' the channels so that enabling sd0 and sd1 buffered
mode will result in scans from the filter filling FIFOs for each of them
but that may not fit the use model you have in mind.
Yes, this model may be an option when we have independent data on each
channel. If we want to handle data correlated in time, things become
more tricky, yet.
The following presentation shows some examples of use cases for STM32
DFSDM (page 20 to 24):
https://st-onlinetraining.s3.amazonaws.com/STM32L4_System_Digital_Filter_for_SD_Modulators_interface_(DFSDM)/index.html
Looking at 3-phase electricity meter example (page 23), the voltages
from three SD modulators are captured and processed by one DFSDM filter.
The mutiplexed filtered data can then be used for further processing.
If we get the filtered data from three SD IIO devices, it looks
difficult to guarantee time alignment between these data.
It seems to me that the solution 2, may reduce the field of use cases
that could be addressed by the DFSDM.
This sort of demux is more often done for when we have a consumer in
the form of say a touchscreen that uses a couple of channels off a
general purpose ADC. We have no reason to want to ensure any alignment
between the data going to the touchscreen and that going to the
who ever is interested in the other ADC channels.
quoted
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
That is indeed the key question. Do we need to configure the modulator
devices? If we do then they need to have an existence in the device model.
Mapping them as IIO devices provides reusability across multiple
filter implementations.
We need to be able to manage a wide range of application. So, we have to
be flexible enough to configure SD modulator when necessary.
I agree, that the SD device has to be kept from this point of view.
quoted
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
That may be an option. It was always on the list of things to do
to allow for IIO devices that have no 'IIO interface' to userspace.
The main usecase was SoC ADCs where all the channels are going to
other in kernel consumers, but it might be applicable here as well.
Can you see another alternative to solution 2, to allow full support of
DFSDM features ?
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Regards
Olivier
quoted
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
Yes.
quoted
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
That one is a rather odd case because no generic handling is possible
of the ADCs. For example it doesn't use the ad7476 driver because we can't
talk to the device even though it's the same ADC as the ad7476 driver supports.
quoted
What is the the preferred approach for you ?
I still favour solution 2, but if you need to have the channels cleanly
presented in a scan despite them coming from different modulators, then that
solution may not be sufficient and we need to think about how else to do
things.
Jonathan
quoted
Thanks for your feedback
Best regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
quoted
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
I'd forgotten about this one, so apologies if it takes me a bit of time to
get back up to speed!
quoted
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
Not a gyroscope driver despite the name :) I was thinking more of the
case where we have a gyroscope that can be wired up to a bunch of different
ADCs.
I wouldn't necessarily take that as a golden example. We were still figuring
out how this stuff would fit together.
From what I recall (and it's been a few years) that device provides no
configuration type interfaces for the SPI ADCs - they end up having no
existence in the device model as a result. There is no means of
sharing anything between the ways this device uses the SPI ADCs and the
way any other device does.
quoted
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
Good point, there isn't a means of combining the scans from multiple
IIO devices and that is what we end up having in this model.
You can 'split' the channels so that enabling sd0 and sd1 buffered
mode will result in scans from the filter filling FIFOs for each of them
but that may not fit the use model you have in mind.
Yes, this model may be an option when we have independent data on each
channel. If we want to handle data correlated in time, things become
more tricky, yet.
The following presentation shows some examples of use cases for STM32
DFSDM (page 20 to 24):
https://st-onlinetraining.s3.amazonaws.com/STM32L4_System_Digital_Filter_for_SD_Modulators_interface_(DFSDM)/index.html
Looking at 3-phase electricity meter example (page 23), the voltages
from three SD modulators are captured and processed by one DFSDM filter.
The mutiplexed filtered data can then be used for further processing.
If we get the filtered data from three SD IIO devices, it looks
difficult to guarantee time alignment between these data.
We can cheat and ensure they all have the same timestamp, but I agree
it is less than ideal.
It seems to me that the solution 2, may reduce the field of use cases
that could be addressed by the DFSDM.
Agreed, that's not good.
quoted
This sort of demux is more often done for when we have a consumer in
the form of say a touchscreen that uses a couple of channels off a
general purpose ADC. We have no reason to want to ensure any alignment
between the data going to the touchscreen and that going to the
who ever is interested in the other ADC channels.
quoted
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
That is indeed the key question. Do we need to configure the modulator
devices? If we do then they need to have an existence in the device model.
Mapping them as IIO devices provides reusability across multiple
filter implementations.
We need to be able to manage a wide range of application. So, we have to
be flexible enough to configure SD modulator when necessary.
I agree, that the SD device has to be kept from this point of view.
quoted
quoted
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
That may be an option. It was always on the list of things to do
to allow for IIO devices that have no 'IIO interface' to userspace.
The main usecase was SoC ADCs where all the channels are going to
other in kernel consumers, but it might be applicable here as well.
Can you see another alternative to solution 2, to allow full support of
DFSDM features ?
Anything I can come up with also has issues.
A) Assume that if we have multiple channels that we want to capture together that
they are going through matched modulator devices. So make the modulator driver
able to handle multiple channels. That way we could wrap it all up together.
Cons: What if they are using different modulators but still want to capture
the data as one scan?
B) Add the logic to mux devices back together (this is nasty but bear with me)
+--------------------+ +--------+ +-----------------+
| Channel interleaver|----| SD0 |---| Filter 0 iiodev |
| | +--------+ | |
| | +--------+ | |
| |----| SD1 |---| |
| | +--------+ +-----------------+
+--------------------+
I did mention this got nasty :) It might be a useful concept in general though
for other usecases.
We introduce a new interleaver device that is a consumer of other devices that
are assumed to all run of the same "trigger". It will be a consumer of
both modulator IIO devices and will receive data from the both.
It will have 2 channels which in turn will gain their scale etc by querying
the modulators. Those modulators will get their actual data as consumers
from the filter device.
So for buffered use the flow will be:
"scan" comes into the filter driver. It demuxes and passes through to the
two separate modulator drivers. Those then pass it on to the channel interleaver.
Given I wouldn't want to constrain the order, that driver then has to buffer
them up until it has a full 'scan' which it in turn pushed into it's kfifo
buffer for userspace consumption.
Other than the horrible data flow, this does match all our requirements.
It represents the filter and any filter specific controls as one device.
Each modulator has it's own representation as well and so scaling etc is
in an appropriate place. The interleaver is then a software construct to
allow us to grab multiple data flows from independent devices (that we
expect to 'trigger' together) and combine them into a single flow.
I'm not keen on the race conditions that would probably occur, but it
could be made to work.
I've thought about doing this before to allow cases like.
Trigger
|
+--------------------+ +-+--------+
| Channel interleaver|--c-| ACCEL |
| | | +--------+
| | +-+--------+
| |----| Gyro |
| | +--------+
+--------------------+
That is an IMU built of separate components but with a common trigger signal
or say a high resolution timer based trigger. Today we have to fuse that
data in userspace which is rather messy.
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Closest example is that rcar-gyroadc but in this case we'd want to define
something standard to support the modulators so that if we have other filters
in future we can reuse them.
That means implementing them as child devices of the filter - probably put
the on the IIO bus, but as different device type. Take a look at how
triggers are done in industrialio-trigger.c
You need struct device_type sd_modulator
and a suitable device struct (burred in an iio_sd_modulator struct probably).
Also needed would be a bunch of standard callbacks to allow you to query things
like scaling. Keep that interface simple. Until we have a lot of modulator
drivers it will be hard to know exactly what is needed. Also whilst we don't
have many it is easy to modify the interface.
Then have your filter driver walk it's own dt children and instantiate
appropriate new elements and register them on the iio_bus. They will have
the filter as their parent.
There are various examples of this sort of thing in tree.
If you want a good one, drivers/cxl does a lot of this sort magic to manage
a fairly complex graph of devices including some nice registration stuff to
cause the correct device drivers to load automatically.
Hmm. Thinking more on this, there is an ordering issue for driver load.
Instead of making the modulator nodes children of the modulator, you may need
to give them their own existence and use a phandle to reference them.
That will let you defer probe in the filter driver until those
modulator drivers are ready.
This isn't going to be particularly simple, so you may want to have a look
at how various other subsystems do similar things and mock up the dependencies
to make sure you have something that doesn't end up with a loop of dependencies.
In some ways the modulators are on a bus below the filter, but the filter driver
needs them to be in place to do the rest.
You may end up with some sort of delayed load.
1. Initial filter driver load + parsing of the modulator dt children (if done that way).
2. Filter driver goes to sleep until...
3. Modulator drivers call something on the filter driver to say they are ready.
4. Filter driver finishes loading and create the IIO device etc.
You'll need some reference counting etc in there to make removal safe etc but it
shouldn't be 'too bad'.
Good luck!
Jonathan
Regards
Olivier
quoted
quoted
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
Yes.
quoted
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
That one is a rather odd case because no generic handling is possible
of the ADCs. For example it doesn't use the ad7476 driver because we can't
talk to the device even though it's the same ADC as the ad7476 driver supports.
quoted
What is the the preferred approach for you ?
I still favour solution 2, but if you need to have the channels cleanly
presented in a scan despite them coming from different modulators, then that
solution may not be sufficient and we need to think about how else to do
things.
Jonathan
quoted
Thanks for your feedback
Best regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
quoted
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
I'd forgotten about this one, so apologies if it takes me a bit of time to
get back up to speed!
quoted
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
Not a gyroscope driver despite the name :) I was thinking more of the
case where we have a gyroscope that can be wired up to a bunch of different
ADCs.
I wouldn't necessarily take that as a golden example. We were still figuring
out how this stuff would fit together.
From what I recall (and it's been a few years) that device provides no
configuration type interfaces for the SPI ADCs - they end up having no
existence in the device model as a result. There is no means of
sharing anything between the ways this device uses the SPI ADCs and the
way any other device does.
quoted
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
Good point, there isn't a means of combining the scans from multiple
IIO devices and that is what we end up having in this model.
You can 'split' the channels so that enabling sd0 and sd1 buffered
mode will result in scans from the filter filling FIFOs for each of them
but that may not fit the use model you have in mind.
Yes, this model may be an option when we have independent data on each
channel. If we want to handle data correlated in time, things become
more tricky, yet.
The following presentation shows some examples of use cases for STM32
DFSDM (page 20 to 24):
https://st-onlinetraining.s3.amazonaws.com/STM32L4_System_Digital_Filter_for_SD_Modulators_interface_(DFSDM)/index.html
Looking at 3-phase electricity meter example (page 23), the voltages
from three SD modulators are captured and processed by one DFSDM filter.
The mutiplexed filtered data can then be used for further processing.
If we get the filtered data from three SD IIO devices, it looks
difficult to guarantee time alignment between these data.
We can cheat and ensure they all have the same timestamp, but I agree
it is less than ideal.
quoted
It seems to me that the solution 2, may reduce the field of use cases
that could be addressed by the DFSDM.
Agreed, that's not good.
quoted
quoted
This sort of demux is more often done for when we have a consumer in
the form of say a touchscreen that uses a couple of channels off a
general purpose ADC. We have no reason to want to ensure any alignment
between the data going to the touchscreen and that going to the
who ever is interested in the other ADC channels.
quoted
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
That is indeed the key question. Do we need to configure the modulator
devices? If we do then they need to have an existence in the device model.
Mapping them as IIO devices provides reusability across multiple
filter implementations.
We need to be able to manage a wide range of application. So, we have to
be flexible enough to configure SD modulator when necessary.
I agree, that the SD device has to be kept from this point of view.
quoted
quoted
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
That may be an option. It was always on the list of things to do
to allow for IIO devices that have no 'IIO interface' to userspace.
The main usecase was SoC ADCs where all the channels are going to
other in kernel consumers, but it might be applicable here as well.
Can you see another alternative to solution 2, to allow full support of
DFSDM features ?
Anything I can come up with also has issues.
A) Assume that if we have multiple channels that we want to capture together that
they are going through matched modulator devices. So make the modulator driver
able to handle multiple channels. That way we could wrap it all up together.
Cons: What if they are using different modulators but still want to capture
the data as one scan?
B) Add the logic to mux devices back together (this is nasty but bear with me)
+--------------------+ +--------+ +-----------------+
| Channel interleaver|----| SD0 |---| Filter 0 iiodev |
| | +--------+ | |
| | +--------+ | |
| |----| SD1 |---| |
| | +--------+ +-----------------+
+--------------------+
I did mention this got nasty :) It might be a useful concept in general though
for other usecases.
We introduce a new interleaver device that is a consumer of other devices that
are assumed to all run of the same "trigger". It will be a consumer of
both modulator IIO devices and will receive data from the both.
It will have 2 channels which in turn will gain their scale etc by querying
the modulators. Those modulators will get their actual data as consumers
from the filter device.
So for buffered use the flow will be:
"scan" comes into the filter driver. It demuxes and passes through to the
two separate modulator drivers. Those then pass it on to the channel interleaver.
Given I wouldn't want to constrain the order, that driver then has to buffer
them up until it has a full 'scan' which it in turn pushed into it's kfifo
buffer for userspace consumption.
Other than the horrible data flow, this does match all our requirements.
It represents the filter and any filter specific controls as one device.
Each modulator has it's own representation as well and so scaling etc is
in an appropriate place. The interleaver is then a software construct to
allow us to grab multiple data flows from independent devices (that we
expect to 'trigger' together) and combine them into a single flow.
I'm not keen on the race conditions that would probably occur, but it
could be made to work.
I've thought about doing this before to allow cases like.
Trigger
|
+--------------------+ +-+--------+
| Channel interleaver|--c-| ACCEL |
| | | +--------+
| | +-+--------+
| |----| Gyro |
| | +--------+
+--------------------+
That is an IMU built of separate components but with a common trigger signal
or say a high resolution timer based trigger. Today we have to fuse that
data in userspace which is rather messy.
In scan mode the DFSDM acts actually as an interleaver, so from this
point of view it can be put at the interleaver place in the flow.
Instead of a software block, we get a driver which represents a hardware
interleaver device. But here we come back to the initial topolgy (case 1
above) with the scaling problem.
I'am wondering if we cannot manage the scale a bit differently.
In the initial proposal, the global scale was exposed at the DFSDM IIO
device. As we have two IIO devices serialized, the global scale could be
calculated at application level from both IIO devices sysfs
informations. The SD modulator would provide the scale (in mV unit) and
the DFSDM could be seen has a device giving a gain.
Currently we have:
data = (raw-dfsdm << shift-dfsdm + offset-dfsdm) x scale-dfsdm
where scale-dfsdm is computed from SD modulator scale info
This may be changed to:
data = (raw-dfsdm << shift-dfsdm + offset-dfsdm) x gain-dfsdm x scale-sd
In this case the DFSDM does not retrieve the scale from SD modulator.
The DFSDM does not provide scale information but only a gain information
(actual resolution / full resolution).
May 'hardwaregain' ABI be a relevant way to describe such gain ?
What looks fine here, is that we remove the dependency between the DFSDM
and the SD modulator, and each IIO device expose consistent sysfs
informations regarding their actual hardware scope.
Does this approach seems valid to you ?
quoted
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Closest example is that rcar-gyroadc but in this case we'd want to define
something standard to support the modulators so that if we have other filters
in future we can reuse them.
That means implementing them as child devices of the filter - probably put
the on the IIO bus, but as different device type. Take a look at how
triggers are done in industrialio-trigger.c
You need struct device_type sd_modulator
and a suitable device struct (burred in an iio_sd_modulator struct probably).
Also needed would be a bunch of standard callbacks to allow you to query things
like scaling. Keep that interface simple. Until we have a lot of modulator
drivers it will be hard to know exactly what is needed. Also whilst we don't
have many it is easy to modify the interface.
Then have your filter driver walk it's own dt children and instantiate
appropriate new elements and register them on the iio_bus. They will have
the filter as their parent.
There are various examples of this sort of thing in tree.
If you want a good one, drivers/cxl does a lot of this sort magic to manage
a fairly complex graph of devices including some nice registration stuff to
cause the correct device drivers to load automatically.
Hmm. Thinking more on this, there is an ordering issue for driver load.
Instead of making the modulator nodes children of the modulator, you may need
to give them their own existence and use a phandle to reference them.
That will let you defer probe in the filter driver until those
modulator drivers are ready.
This isn't going to be particularly simple, so you may want to have a look
at how various other subsystems do similar things and mock up the dependencies
to make sure you have something that doesn't end up with a loop of dependencies.
In some ways the modulators are on a bus below the filter, but the filter driver
needs them to be in place to do the rest.
You may end up with some sort of delayed load.
1. Initial filter driver load + parsing of the modulator dt children (if done that way).
2. Filter driver goes to sleep until...
3. Modulator drivers call something on the filter driver to say they are ready.
4. Filter driver finishes loading and create the IIO device etc.
You'll need some reference counting etc in there to make removal safe etc but it
shouldn't be 'too bad'.
Good luck!
Jonathan
The device hierachy you have detailled above, is probably the most
flexible one to address a wide range of use cases, but it is quite a
huge work ... especially in comparison to current need.
Thanks anyway for all the hints you gave here.
Regards
Olivier
quoted
Regards
Olivier
quoted
quoted
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
Yes.
quoted
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
That one is a rather odd case because no generic handling is possible
of the ADCs. For example it doesn't use the ad7476 driver because we can't
talk to the device even though it's the same ADC as the ad7476 driver supports.
quoted
What is the the preferred approach for you ?
I still favour solution 2, but if you need to have the channels cleanly
presented in a scan despite them coming from different modulators, then that
solution may not be sufficient and we need to think about how else to do
things.
Jonathan
quoted
Thanks for your feedback
Best regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
Hi Jonathan,
On 9/10/21 4:05 PM, Olivier MOYSAN wrote:
quoted
ST Restricted
-----Original Message-----
From: Jonathan Cameron <jic23@kernel.org>
Sent: vendredi 14 février 2020 16:10
To: Olivier MOYSAN <redacted>
Cc: robh+dt@kernel.org; mark.rutland@arm.com; knaack.h@gmx.de; lars@metafoo.de; devicetree@vger.kernel.org; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org; pmeerw@pmeerw.net; linux-stm32@st-md-mailman.stormreply.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support
On Fri, 14 Feb 2020 14:49:18 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/14/20 2:11 PM, Jonathan Cameron wrote:
quoted
On Tue, 11 Feb 2020 15:19:01 +0000
Olivier MOYSAN [off-list ref] wrote:
quoted
Hi Jonathan,
On 2/8/20 5:18 PM, Jonathan Cameron wrote:
quoted
On Tue, 4 Feb 2020 11:10:08 +0100
Olivier Moysan [off-list ref] wrote:
quoted
Add scale and offset attributes support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <redacted>
Hmm. I can't remember this history of this but we've kind of ended
up backwards wrt to other consumer drivers.
In some sense this is similar to the analog gyroscopes. In those
the consumer driver is the gyroscope which is consuming the raw
readings from an ADC connected to the channel. This results in us
getting readings reported by the gyroscope driver.
Here we have a sigma delta convertor consuming the pulse train
from a sigma delta device. So the channels are reported by the
sigma delta receiver, whereas i think the nearest equivalent to
the analog voltage outputing gyroscopes would have been if we had
reported the channel values at the sigma delta converter.
The DFSDM driver is currently used as a consumer of the sd modulator.
The scale and offset values of the channels are already computed by
the DFSDM driver, and provided by this driver to the IIO ABI.
However, the DFSDM has no voltage reference, so it has to retrieve
it from sd-modulator channels, for the scale factor computation.
scale offset
^ ^
| | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output input
^
| vref
+
Is it the topology your are expecting ?
It's not the one we'd expect if we are aligning with similar cases
elsewhere in IIO. For example, if we attach an analog accelerometer
to an ADC, we report the accel channels on the accelerometer not the
ADC. The equivalent would be to see the DFSDM as providing a
conversion service to the SD device which is actually executing the
measurement and has the input channels.
scale offset raw
^ ^ ^
| | | IIO ABI
+-------------------------------------------------------------+
+---------------+ +-------------+
|sd driver | |DFSDM driver |
+---------------+ +-------------+
+-------------------------------------------------------------+
HW
+---------------+ +-------------+
+------->+ sd-modulator +--------->+ DFSDM +-------->
analog +------+--------+ +-------------+ output
input ^
| vref
quoted
+
Thanks for your clarification.
ok, moving to this logic is a significant change.
I need to evaluate further the impact on the dfsdm driver.
Understood! If we can't do it without potentially breaking users then such is life.
Jonathan
I come back to this old, but still valid topic.
I'd forgotten about this one, so apologies if it takes me a bit of time to
get back up to speed!
quoted
You mentioned the example of analog gyroscopes in a previous message.
Looking at gyroscope drivers, I found rcar-gyroadc driver which shows
Not a gyroscope driver despite the name :) I was thinking more of the
case where we have a gyroscope that can be wired up to a bunch of different
ADCs.
I wouldn't necessarily take that as a golden example. We were still figuring
out how this stuff would fit together.
From what I recall (and it's been a few years) that device provides no
configuration type interfaces for the SPI ADCs - they end up having no
existence in the device model as a result. There is no means of
sharing anything between the ways this device uses the SPI ADCs and the
way any other device does.
quoted
I took the example of gyroadc to reconsider dfsdm topology and explore
some variants according to IIO devices use.
1) current topology: one IIO device per SD modulator and one iio device
per DFSDM filter
The DFSDM is used as a consumer of SD modulator through the hw
consumer API.
* cons
- SD modulator and DFSDM filter have their own channel
specification.
- DFSDM retrieves channels scale information from SD
modulator to initialized its channels
- SD modulator IIO sysfs interface is useless
+------------+ +-------+ +---------+ sysfs
| sd0 iiodev | --> | chan0 | --> | filter0 | ------->
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | --> | chan1 | ------+
+------------+ +-------+
|
| sysfs
v
2) "conversion service" topology: one IIO device per SD modulator
* cons
- Data transfers: in this case the converted data from
DFSDM filter have to be sent back to SD modulator to be
available on sysfs interface.
- Scan mode: this topology seems not compatible with scan
mode, where multiplexed channels are expected are on
IIO device interface.
=> I don't find a proper way to address scan mode with multi SD
modulator connected to one DFSM filter
Good point, there isn't a means of combining the scans from multiple
IIO devices and that is what we end up having in this model.
You can 'split' the channels so that enabling sd0 and sd1 buffered
mode will result in scans from the filter filling FIFOs for each of them
but that may not fit the use model you have in mind.
Yes, this model may be an option when we have independent data on each
channel. If we want to handle data correlated in time, things become
more tricky, yet.
The following presentation shows some examples of use cases for STM32
DFSDM (page 20 to 24):
https://st-onlinetraining.s3.amazonaws.com/STM32L4_System_Digital_Filter_for_SD_Modulators_interface_(DFSDM)/index.html
Looking at 3-phase electricity meter example (page 23), the voltages
from three SD modulators are captured and processed by one DFSDM filter.
The mutiplexed filtered data can then be used for further processing.
If we get the filtered data from three SD IIO devices, it looks
difficult to guarantee time alignment between these data.
We can cheat and ensure they all have the same timestamp, but I agree
it is less than ideal.
quoted
It seems to me that the solution 2, may reduce the field of use cases
that could be addressed by the DFSDM.
Agreed, that's not good.
quoted
quoted
This sort of demux is more often done for when we have a consumer in
the form of say a touchscreen that uses a couple of channels off a
general purpose ADC. We have no reason to want to ensure any alignment
between the data going to the touchscreen and that going to the
who ever is interested in the other ADC channels.
quoted
+------------+ +-------+ +---------+
| sd0 iiodev | <--> | chan0 | <-> | filter0 |
+------------+ +-------+ +---------+
| ^
| sysfs |
v |
|
|
|
+------------+ +-------+ |
| sd1 iiodev | <--> | chan1 | <-----+
+------------+ +-------+
|
| sysfs
v
3) gyroadc like topology: one iio device per DFSDM filter
(no SD modulator iio device registered)
For DFSDM scale and offset, the required information are SD
modulator reference voltage and channel types.
voltage reference: the regulator voltage can be retrieved as it
is done in gyroadc driver.
Maybe we can dropped merely SD modulator, and describe voltage
as a property of the channel (through generic channel binding)
This may be too restrictive if more hardware has to be
configured in the SD modulator, yet.
That is indeed the key question. Do we need to configure the modulator
devices? If we do then they need to have an existence in the device model.
Mapping them as IIO devices provides reusability across multiple
filter implementations.
We need to be able to manage a wide range of application. So, we have to
be flexible enough to configure SD modulator when necessary.
I agree, that the SD device has to be kept from this point of view.
quoted
quoted
channel type: IIO generic channel binding could be used here
instead of proprietary properties
to describe the channels
binding sample:
dfsdm_pdm1: filter@1 {
compatible = "st,stm32-dfsdm-adc";
reg = <1>;
interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_HIGH>;
dmas = <&dmamux1 102 0x400 0x01>;
dma-names = "rx";
st,filter-order = <1>;
channel@2 {
reg = <2>;
label = "in2";
st,adc-channel-types = "SPI_R";
st,adc-channel-clk-src = "CLKOUT_F";
sd@0 { ?
reg = <0>;
compatible = "sd-mod";
vref-supply = <&vref>;
};
};
};
* cons
- The sub devices are embedded in the driver and are not
based on general device API.
Alternatively, if we want to use standard device model
and avoid the creation of an unrelevant IIO device for
SD modulator, a specific type of device may be
provided by IIO framework. This could be a kind of
"backend" device without IIO sysfs interface attached.
That may be an option. It was always on the list of things to do
to allow for IIO devices that have no 'IIO interface' to userspace.
The main usecase was SoC ADCs where all the channels are going to
other in kernel consumers, but it might be applicable here as well.
Can you see another alternative to solution 2, to allow full support of
DFSDM features ?
Anything I can come up with also has issues.
A) Assume that if we have multiple channels that we want to capture together that
they are going through matched modulator devices. So make the modulator driver
able to handle multiple channels. That way we could wrap it all up together.
Cons: What if they are using different modulators but still want to capture
the data as one scan?
B) Add the logic to mux devices back together (this is nasty but bear with me)
+--------------------+ +--------+ +-----------------+
| Channel interleaver|----| SD0 |---| Filter 0 iiodev |
| | +--------+ | |
| | +--------+ | |
| |----| SD1 |---| |
| | +--------+ +-----------------+
+--------------------+
I did mention this got nasty :) It might be a useful concept in general though
for other usecases.
We introduce a new interleaver device that is a consumer of other devices that
are assumed to all run of the same "trigger". It will be a consumer of
both modulator IIO devices and will receive data from the both.
It will have 2 channels which in turn will gain their scale etc by querying
the modulators. Those modulators will get their actual data as consumers
from the filter device.
So for buffered use the flow will be:
"scan" comes into the filter driver. It demuxes and passes through to the
two separate modulator drivers. Those then pass it on to the channel interleaver.
Given I wouldn't want to constrain the order, that driver then has to buffer
them up until it has a full 'scan' which it in turn pushed into it's kfifo
buffer for userspace consumption.
Other than the horrible data flow, this does match all our requirements.
It represents the filter and any filter specific controls as one device.
Each modulator has it's own representation as well and so scaling etc is
in an appropriate place. The interleaver is then a software construct to
allow us to grab multiple data flows from independent devices (that we
expect to 'trigger' together) and combine them into a single flow.
I'm not keen on the race conditions that would probably occur, but it
could be made to work.
I've thought about doing this before to allow cases like.
Trigger
|
+--------------------+ +-+--------+
| Channel interleaver|--c-| ACCEL |
| | | +--------+
| | +-+--------+
| |----| Gyro |
| | +--------+
+--------------------+
That is an IMU built of separate components but with a common trigger signal
or say a high resolution timer based trigger. Today we have to fuse that
data in userspace which is rather messy.
In scan mode the DFSDM acts actually as an interleaver, so from this
point of view it can be put at the interleaver place in the flow.
Instead of a software block, we get a driver which represents a hardware
interleaver device. But here we come back to the initial topolgy (case 1
above) with the scaling problem.
I'd go with 'sort of' for it matching that topology. I agree it's
doing the hardware job of measuring the multiple channels, but it
doesn't represent the data flow of multiple unrelated devices infront
of the dfsdm.
It's bit clunky as an analogy but imagine this maps to.
Interleaver represents some 'physical thing' - in the example of
accel and gyro it's a physical device we are moving around. We ultimately
want a single data stream to tell us how that is moving.
It has a bunch of properties which we are then measuring with
a gyro and an accelerometer (which generate an analog signal). Those
measurements are then in turn obtained by using an ADC.
Still, whether this actually maps usefully to what we have here isn't
totally clear to me.
I'am wondering if we cannot manage the scale a bit differently.
In the initial proposal, the global scale was exposed at the DFSDM IIO
device. As we have two IIO devices serialized, the global scale could be
calculated at application level from both IIO devices sysfs
informations. The SD modulator would provide the scale (in mV unit) and
the DFSDM could be seen has a device giving a gain.
Currently we have:
data = (raw-dfsdm << shift-dfsdm + offset-dfsdm) x scale-dfsdm
where scale-dfsdm is computed from SD modulator scale info
This may be changed to:
data = (raw-dfsdm << shift-dfsdm + offset-dfsdm) x gain-dfsdm x scale-sd
In this case the DFSDM does not retrieve the scale from SD modulator.
The DFSDM does not provide scale information but only a gain information
(actual resolution / full resolution).
May 'hardwaregain' ABI be a relevant way to describe such gain ?
Hardware gain is a bit of oddity.
Normally hardwaregain is applied to devices where
the gain isn't on the the 'thing being measured' but on something else that
affects that measurement. An example being the gain of the light sensor used
in a time of flight distance measurement.
However, we have used in cases where we have an amplifier that is typically
amplifying signals not actually visible to us, for example the ad8366
which I think get used as a baseband amplifier in radio applications.
+---------+
Some analog signal ----->|AMPLIFIER|-----> some other analog signal, not heading to an ADC.
+---------+
What looks fine here, is that we remove the dependency between the DFSDM
and the SD modulator, and each IIO device expose consistent sysfs
informations regarding their actual hardware scope.
Does this approach seems valid to you ?
Loosing the dependency removes an obvious way for generic software to
actually understand what is going on. That software just wants to measure
an analog signal, not figure out the wiring diagram of the components in
the path.
quoted
quoted
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Closest example is that rcar-gyroadc but in this case we'd want to define
something standard to support the modulators so that if we have other filters
in future we can reuse them.
That means implementing them as child devices of the filter - probably put
the on the IIO bus, but as different device type. Take a look at how
triggers are done in industrialio-trigger.c
You need struct device_type sd_modulator
and a suitable device struct (burred in an iio_sd_modulator struct probably).
Also needed would be a bunch of standard callbacks to allow you to query things
like scaling. Keep that interface simple. Until we have a lot of modulator
drivers it will be hard to know exactly what is needed. Also whilst we don't
have many it is easy to modify the interface.
Then have your filter driver walk it's own dt children and instantiate
appropriate new elements and register them on the iio_bus. They will have
the filter as their parent.
There are various examples of this sort of thing in tree.
If you want a good one, drivers/cxl does a lot of this sort magic to manage
a fairly complex graph of devices including some nice registration stuff to
cause the correct device drivers to load automatically.
Hmm. Thinking more on this, there is an ordering issue for driver load.
Instead of making the modulator nodes children of the modulator, you may need
to give them their own existence and use a phandle to reference them.
That will let you defer probe in the filter driver until those
modulator drivers are ready.
This isn't going to be particularly simple, so you may want to have a look
at how various other subsystems do similar things and mock up the dependencies
to make sure you have something that doesn't end up with a loop of dependencies.
In some ways the modulators are on a bus below the filter, but the filter driver
needs them to be in place to do the rest.
You may end up with some sort of delayed load.
1. Initial filter driver load + parsing of the modulator dt children (if done that way).
2. Filter driver goes to sleep until...
3. Modulator drivers call something on the filter driver to say they are ready.
4. Filter driver finishes loading and create the IIO device etc.
You'll need some reference counting etc in there to make removal safe etc but it
shouldn't be 'too bad'.
Good luck!
Jonathan
The device hierachy you have detailled above, is probably the most
flexible one to address a wide range of use cases, but it is quite a
huge work ... especially in comparison to current need.
Understood. Maybe its something we can evolve towards over time.
I'd like to say I'll get time sometime in the near future to put a prototype
together but sadly I have too many other things on the todo list to commit
to anything.
Jonathan
Thanks anyway for all the hints you gave here.
No problem. These stm32 parts manage to continue pushing the boundaries
of our rather simplified model of how the world works!
Jonathan
Regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
=> This solution could be applicable but some details in the
implementation will have to be clarified further.
May we consider adding a "backend" device without IIO interface
in the IIO framework ?
May the SD modulator be dropped ?
+-----+ +-------+ +----------------+ sysfs
| sd0 | --> | chan0 | --> | filter0 iiodev | ------->
+-----+ +-------+ +----------------+
^
|
|
+-----+ +-------+ |
| sd1 | --> | chan1 | ------+
+-----+ +-------+
Here there is a point that needs to be clarified in relation to the
previous discussions I think.
If I refer to the last comment of the current thread, I understand that
you were expecting the IIO sysfs interface to be attached to the SD
modulator. (solution 2)
Yes.
quoted
For the gyroadc, the channels are indeed populated by the sub devices.
However the IIO device corresponds to the ADC consumer and not the ADCs
themselves. (solution 3)
That one is a rather odd case because no generic handling is possible
of the ADCs. For example it doesn't use the ad7476 driver because we can't
talk to the device even though it's the same ADC as the ad7476 driver supports.
quoted
What is the the preferred approach for you ?
I still favour solution 2, but if you need to have the channels cleanly
presented in a scan despite them coming from different modulators, then that
solution may not be sufficient and we need to think about how else to do
things.
Jonathan
quoted
Thanks for your feedback
Best regards
Olivier
quoted
quoted
Regards
Olivier
quoted
quoted
If not, I probably missedsomething. Could you please clarify this point ?
Regards
Olivier
quoted
This wasn't really an issue when the only values available were
raw, but if we are adding scale and offset, they are things that
belong to the ad1201 for example, not the upstream stm32-dfsdm unit.
Thinking of it another way, we don't report an SPI ADC output in
the driver for the SPI master.
Could we flip it around without breaking anything?
Jonathan
@@ struct stm32_dfsdm_adc {structiio_hw_consumer*hwc;structcompletioncompletion;u32*buffer;+structstm32_dfsdm_sd_chan_info*sd_chan;/* Audio specific */unsignedintspi_freq;/* SPI bus clock frequency */@@-1271,7+1280,10@@staticintstm32_dfsdm_read_raw(structiio_dev*indio_dev,int*val2,longmask){structstm32_dfsdm_adc*adc=iio_priv(indio_dev);-intret;+structstm32_dfsdm_filter*fl=&adc->dfsdm->fl_list[adc->fl_id];+structstm32_dfsdm_filter_osr*flo=&fl->flo[fl->fast];+u32max=flo->max<<(flo->lshift-chan->scan_type.shift);+intret,idx=chan->scan_index;switch(mask){caseIIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,*val=adc->sample_freq;returnIIO_VAL_INT;++caseIIO_CHAN_INFO_SCALE:+/*+*ScaleisexpressedinmV.+*Whenfastmodeisdisabled,actualresolutionmaybelower+*than2^n,wheren=realbits-1.+*Thisleadstounderestimatinginputvoltage.To+*compensatethisdeviation,thevoltagereferencecanbe+*correctedwithafactor=realbitsresolution/actualmax+*/+*val=div_u64((u64)adc->sd_chan[idx].scale_val*+(u64)BIT(DFSDM_DATA_RES-1),max);+*val2=chan->scan_type.realbits;+if(adc->sd_chan[idx].differential)+*val*=2;++returnIIO_VAL_FRACTIONAL_LOG2;++caseIIO_CHAN_INFO_OFFSET:+/*+*DFSDMoutputdataareintherange[-2^n,2^n-1],+*withn=realbits-1.+*-Differentialmodulator:+*OffsetcorrespondtoSDmodulatoroffset.+*-Singleendedmodulator:+*Inputisin[0V,Vref]range,where0Vcorrespondsto-2^n.+*Add2^ntooffset.(i.e.middleofinputrange)+*offset=offset(sd)*vref/res(sd)*max/vref.+*/+*val=div_u64((u64)max*adc->sd_chan[idx].offset,+BIT(adc->sd_chan[idx].scale_val2-1));+if(!adc->sd_chan[idx].differential)+*val+=max;++returnIIO_VAL_INT;}return-EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,*IIO_CHAN_INFO_RAW:usedtocomputeregularconversion*IIO_CHAN_INFO_OVERSAMPLING_RATIO:usedtosetoversampling*/-ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW);+ch->info_mask_separate=BIT(IIO_CHAN_INFO_RAW)|+BIT(IIO_CHAN_INFO_SCALE)|+BIT(IIO_CHAN_INFO_OFFSET);ch->info_mask_shared_by_all=BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO)|BIT(IIO_CHAN_INFO_SAMP_FREQ);
@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev){structiio_chan_spec*ch;structstm32_dfsdm_adc*adc=iio_priv(indio_dev);+structiio_channel*channels,*chan;+structstm32_dfsdm_sd_chan_info*sd_chan;intnum_ch;-intret,chan_idx;+intret,chan_idx,val2;adc->oversamp=DFSDM_DEFAULT_OVERSAMPLING;ret=stm32_dfsdm_compute_all_osrs(indio_dev,adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)if(!ch)return-ENOMEM;+/* Get SD modulator channels */+channels=iio_channel_get_all(&indio_dev->dev);+if(IS_ERR(channels)){+dev_err(&indio_dev->dev,"Failed to get channel %ld\n",+PTR_ERR(channels));+returnPTR_ERR(channels);+}+chan=&channels[0];++adc->sd_chan=devm_kzalloc(&indio_dev->dev,+sizeof(*adc->sd_chan)*num_ch,GFP_KERNEL);+if(!adc->sd_chan)+return-ENOMEM;++sd_chan=adc->sd_chan;+for(chan_idx=0;chan_idx<num_ch;chan_idx++){ch[chan_idx].scan_index=chan_idx;ret=stm32_dfsdm_adc_chan_init_one(indio_dev,
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Closest example is that rcar-gyroadc but in this case we'd want to define
something standard to support the modulators so that if we have other filters
in future we can reuse them.
That means implementing them as child devices of the filter - probably put
the on the IIO bus, but as different device type. Take a look at how
triggers are done in industrialio-trigger.c
You need struct device_type sd_modulator
and a suitable device struct (burred in an iio_sd_modulator struct probably).
Also needed would be a bunch of standard callbacks to allow you to query things
like scaling. Keep that interface simple. Until we have a lot of modulator
drivers it will be hard to know exactly what is needed. Also whilst we don't
have many it is easy to modify the interface.
Then have your filter driver walk it's own dt children and instantiate
appropriate new elements and register them on the iio_bus. They will have
the filter as their parent.
There are various examples of this sort of thing in tree.
If you want a good one, drivers/cxl does a lot of this sort magic to manage
a fairly complex graph of devices including some nice registration stuff to
cause the correct device drivers to load automatically.
Hmm. Thinking more on this, there is an ordering issue for driver load.
Instead of making the modulator nodes children of the modulator, you may need
to give them their own existence and use a phandle to reference them.
That will let you defer probe in the filter driver until those
modulator drivers are ready.
This isn't going to be particularly simple, so you may want to have a look
at how various other subsystems do similar things and mock up the dependencies
to make sure you have something that doesn't end up with a loop of dependencies.
In some ways the modulators are on a bus below the filter, but the filter driver
needs them to be in place to do the rest.
You may end up with some sort of delayed load.
1. Initial filter driver load + parsing of the modulator dt children (if done that way).
2. Filter driver goes to sleep until...
3. Modulator drivers call something on the filter driver to say they are ready.
4. Filter driver finishes loading and create the IIO device etc.
You'll need some reference counting etc in there to make removal safe etc but it
shouldn't be 'too bad'.
Good luck!
Jonathan
I'am on the way to prototype this proposal for DFSDM.
Looking at your advices, I see that the current topolgy based on
hardware consumer, already meets most of the requirements.
- SD modulators are described in DT with their own nodes and are
referred in DFSDM nodes through their phandle.
- Dependencies at probe are managed (defer probe through
devm_iio_hw_consumer_alloc())
- SD modulator scaling is retrieved through iio_read_channel_scale() ABI.
So, it seems that the current implementation is not so far from this
solution.
It remains the unwanted sysfs interface for SD modulator. Or more than
that, if I missed something ?
Instead of introducing a new device type for SD modulator, could the
mode field be used to identify devices not requesting an IIO sysfs ?
(A dedicated mode may be used to skip sysfs register in device registration)
Otherwise let's go for a new type.
Regards
Olivier
If 'backend' option turns out to be the most appropriated to match DFSDM
constraints, I can prepare some patches to support it.
Would you have some guidelines or requirements for the implementation of
such feature, in this case ?
Closest example is that rcar-gyroadc but in this case we'd want to define
something standard to support the modulators so that if we have other filters
in future we can reuse them.
That means implementing them as child devices of the filter - probably put
the on the IIO bus, but as different device type. Take a look at how
triggers are done in industrialio-trigger.c
You need struct device_type sd_modulator
and a suitable device struct (burred in an iio_sd_modulator struct probably).
Also needed would be a bunch of standard callbacks to allow you to query things
like scaling. Keep that interface simple. Until we have a lot of modulator
drivers it will be hard to know exactly what is needed. Also whilst we don't
have many it is easy to modify the interface.
Then have your filter driver walk it's own dt children and instantiate
appropriate new elements and register them on the iio_bus. They will have
the filter as their parent.
There are various examples of this sort of thing in tree.
If you want a good one, drivers/cxl does a lot of this sort magic to manage
a fairly complex graph of devices including some nice registration stuff to
cause the correct device drivers to load automatically.
Hmm. Thinking more on this, there is an ordering issue for driver load.
Instead of making the modulator nodes children of the modulator, you may need
to give them their own existence and use a phandle to reference them.
That will let you defer probe in the filter driver until those
modulator drivers are ready.
This isn't going to be particularly simple, so you may want to have a look
at how various other subsystems do similar things and mock up the dependencies
to make sure you have something that doesn't end up with a loop of dependencies.
In some ways the modulators are on a bus below the filter, but the filter driver
needs them to be in place to do the rest.
You may end up with some sort of delayed load.
1. Initial filter driver load + parsing of the modulator dt children (if done that way).
2. Filter driver goes to sleep until...
3. Modulator drivers call something on the filter driver to say they are ready.
4. Filter driver finishes loading and create the IIO device etc.
You'll need some reference counting etc in there to make removal safe etc but it
shouldn't be 'too bad'.
Good luck!
Jonathan
I'am on the way to prototype this proposal for DFSDM.
Looking at your advices, I see that the current topolgy based on
hardware consumer, already meets most of the requirements.
- SD modulators are described in DT with their own nodes and are
referred in DFSDM nodes through their phandle.
- Dependencies at probe are managed (defer probe through
devm_iio_hw_consumer_alloc())
- SD modulator scaling is retrieved through iio_read_channel_scale() ABI.
So, it seems that the current implementation is not so far from this
solution.
It remains the unwanted sysfs interface for SD modulator. Or more than
that, if I missed something ?
Instead of introducing a new device type for SD modulator, could the
mode field be used to identify devices not requesting an IIO sysfs ?
(A dedicated mode may be used to skip sysfs register in device registration)
Otherwise let's go for a new type.
I'd rather see them as a new device type than overload the IIO device.
We want to be able to control what can 'connect' to the DFSDM afterall
and device type is a convenient route to doing this.
Obviously if there is infrastructure that can be factored out and used
for both this and a normal IIO device we can do that to save on duplication.
Thanks,
Jonathan