Re: [RFC PATCH v4 1/1] iio/scmi: Adding support for IIO SCMI Based Sensors

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Date: 2021-02-05 12:37:53
Also in: lkml

On Thu, 4 Feb 2021 10:20:43 -0800
Jyoti Bhayana [off-list ref] wrote:

Hi Jonathan,

Thanks for the clarification. One last question:

quoted

Instead of using the read_avail callback (which I'd normally much prefer)
you can just do what lots of drivers in IIO do (predate the callback) and
provide your own implementation of the attribute.

Regarding your comment above to provide our own implementation of the
attribute, I had the following attributes defined in V1 of the patch for
max_range and resolution.

+static IIO_DEVICE_ATTR(sensor_max_range, 0444,
scmi_iio_get_sensor_max_range,
+                      NULL, 0);
+static IIO_DEVICE_ATTR(sensor_resolution, 0444,
scmi_iio_get_sensor_resolution,
+                      NULL, 0);

So do you mean that it is ok to put these two attributes back?

No that would definite ABI that doesn't already exist and doesn't
fit with the general way the ABI works.  You can however do something like

static IIO_DEVICE_ATTR(in_accel_raw_avail, 0444, NULL, 0);

That should result in an element int he standard ABI but let you define
your own implementation.

Also, in v1
of the implementation sensor_resolution has the scale already applied as it
is using a different exponent than sensor scale as discussed before. And
sensor_range is raw value and user space needs to apply the sensor scale.

There is only one scale that is exposed to userspace.  The ABI doesn't allow
for any other so if you do add a second one no userspace space software will use
it.  Hence you need to do the maths inside the driver to present the value such
that when the userspace scale is applied you get the right number irrespective
of what is peing provided from SCMI.

Is it ok to keep sensor_resolution like that or I would need to do the
calculation to divide the sensor_resolution by sensor scale and provide the
raw value for resolution instead?

Exactly - you will need to do that calculation.  It makes no sense to have
a userspace interface that allows for these to be in different units.

Also sensor resolution will be
float/double and sensor max range will be long long (int64) as no floating
point is needed for that.

You are printing a string from the attr, so it shouldn't matter.
[131313 1.312344 224456677] (with appropriate numbers and potentially a lot
more digits) should be fine.  We don't have many users of _raw_avail yet
(and I think they are all DACs).  Not min might well be negative depending on
sensor type and offsets etc.

As a side note, the real values the sensor is providing have to be expressed
as an integer (be it a 64 bit one potentially) * a fixed scale.
As all values have to fit that, logically the resolution when converted to
these units must also be an integer whether or not the specification technically
requires that.  As I understand it, it represents a step between neighbouring
values and those must both be represented as 64 bit integers or they can't
be passed through the interface.

Let me know if that will be fine. I do not have
sensor min range exposed as an attribute as that is not currently needed in
our use case. So I am assuming it will be fine to just have these two
attributes mentioned above for max range and resolution?

No, whilst we can extend the ABI (with a cost given that means you have userspace
that doesn't recognise new stuff) we need to remain inline with the ABI
in order to maintain consistency across different sensors.
Doing that is most of what makes a Linux subsystem work rather than just being
a collection of drivers, each with their own magic.

Sorry this discussion has taken so many rounds.  Unfortunately that
SCMI spec does some things that make no sense whatsoever for any situation with
direct interaction with a sensor.

The way resolution is expressed still has me more than a little bemused.

Jonathan


Thanks,
Jyoti

On Thu, Feb 4, 2021 at 9:00 AM Jonathan Cameron [off-list ref]
wrote:

quoted

On Mon, 1 Feb 2021 22:53:18 -0800
Jyoti Bhayana [off-list ref] wrote:

quoted

Hi Jonathan,

I wanted to clarify a few things before I upload the next version of
the patch. Can you please help provide some more details regarding the
following questions?

1) You mentioned that  
      > perhaps we just need to do the maths in here rather than rely  
on core handling of IIO_VAL_FRACTIONAL.  
       > That would give us a greater potential range"  

        Can you please clarify with some examples of how I can use
IIO_VAL_INT_PLUS_MICRO to represent a range which is larger than 32
bits without changing the sensor scale?

Sorry I wasn't clear on what I meant here.
Instead of using the read_avail callback (which I'd normally much prefer)
you can just do what lots of drivers in IIO do (predate the callback) and
provide your own implementation of the attribute.  Then you can do
whatever precision of maths you like to generate the string that is
printed.   Any userspace code reading more decimal places than they
expect to see (using 32 bit float perhaps rather than a double) will
just round it I think.

quoted

2)  > #define ilog10(x) (ilog2(x) / const_ilog2(10))  
     > That feels like it's probably not great for precision"  
 I am only using this calculation to get the power of 10 multiplier
used when setting the scmi sensor update interval, so the exact
precision after the decimal point is not necessary.  I am only using
at one place in the code, so either I can remove the #define and
directly use it in the function or change the name of the #define.
Please let me know what you think

Put it inline as we probably don't want an ilog10 macro.
Sooner or later someone will add one to a generic header with resulting
confusion.

quoted

3)

quoted

+#define UHZ_PER_HZ 1000000UL
+#define ODR_EXPAND(odr, uodr) (((odr) * 1000000ULL) + (uodr))

quoted

Prefix these if driver specific.
For those that aren't perhaps we can think about putting them in
generic headers

UHZ_PER_HZ is generic and not driver specific. Either I can use
USEC_PER_SEC which is already defined in include/linux/time64.h or we
can put UHZ_PER_HZ in a generic header instead. Please let me know
your preference and also which header file you think it needs to be
added in case of generic header.

It's only used in two places, I'd be tempted to just use the numeric
value.  Or perhaps define it locally to them.

quoted

ODR_EXPAND is only used in one place in the code, and I can remove the
#define and use it directly in the function. Let me know if that will
be fine with you,

That's fine.

quoted

Thanks,
Jyoti






On Sun, Jan 31, 2021 at 5:11 AM Jonathan Cameron [off-list ref]

wrote:

quoted

On Fri, 29 Jan 2021 22:18:18 +0000
Jyoti Bhayana [off-list ref] wrote:

quoted

This change provides ARM SCMI Protocol based IIO device.
This driver provides support for Accelerometer and Gyroscope using
SCMI Sensor Protocol extensions added in the SCMIv3.0 ARM

specification

quoted

Signed-off-by: Jyoti Bhayana <jbhayana@google.com>

A few minor things noticed on a fresh read through, but mostly I think
we are down to figuring out how to deal with the range (as discussed
in the thread continuing on v3).

On another note, probably time to drop the RFC or give a bit more

detail

quoted

on why you think this isn't ready to be applied.

Thanks,

Jonathan

quoted

---
 MAINTAINERS                                |   6 +
 drivers/iio/common/Kconfig                 |   1 +
 drivers/iio/common/Makefile                |   1 +
 drivers/iio/common/scmi_sensors/Kconfig    |  18 +
 drivers/iio/common/scmi_sensors/Makefile   |   5 +
 drivers/iio/common/scmi_sensors/scmi_iio.c | 742

+++++++++++++++++++++

quoted

 6 files changed, 773 insertions(+)
 create mode 100644 drivers/iio/common/scmi_sensors/Kconfig
 create mode 100644 drivers/iio/common/scmi_sensors/Makefile
 create mode 100644 drivers/iio/common/scmi_sensors/scmi_iio.c

diff --git a/MAINTAINERS b/MAINTAINERS
index b516bb34a8d5..ccf37d43ab41 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -8567,6 +8567,12 @@ S:     Maintained
 F:

 Documentation/devicetree/bindings/iio/multiplexer/io-channel-mux.txt

quoted

 F:   drivers/iio/multiplexer/iio-mux.c

+IIO SCMI BASED DRIVER
+M:   Jyoti Bhayana [off-list ref]
+L:   linux-iio@vger.kernel.org
+S:   Maintained
+F:   drivers/iio/common/scmi_sensors/scmi_iio.c
+
 IIO SUBSYSTEM AND DRIVERS
 M:   Jonathan Cameron [off-list ref]
 R:   Lars-Peter Clausen [off-list ref]

diff --git a/drivers/iio/common/Kconfig b/drivers/iio/common/Kconfig
index 2b9ee9161abd..0334b4954773 100644
--- a/drivers/iio/common/Kconfig
+++ b/drivers/iio/common/Kconfig

@@ -6,5 +6,6 @@
 source "drivers/iio/common/cros_ec_sensors/Kconfig"
 source "drivers/iio/common/hid-sensors/Kconfig"
 source "drivers/iio/common/ms_sensors/Kconfig"
+source "drivers/iio/common/scmi_sensors/Kconfig"
 source "drivers/iio/common/ssp_sensors/Kconfig"
 source "drivers/iio/common/st_sensors/Kconfig"

diff --git a/drivers/iio/common/Makefile

b/drivers/iio/common/Makefile

quoted

index 4bc30bb548e2..fad40e1e1718 100644

--- a/drivers/iio/common/Makefile
+++ b/drivers/iio/common/Makefile

@@ -11,5 +11,6 @@
 obj-y += cros_ec_sensors/
 obj-y += hid-sensors/
 obj-y += ms_sensors/
+obj-y += scmi_sensors/
 obj-y += ssp_sensors/
 obj-y += st_sensors/

diff --git a/drivers/iio/common/scmi_sensors/Kconfig

b/drivers/iio/common/scmi_sensors/Kconfig

quoted

new file mode 100644
index 000000000000..67e084cbb1ab

--- /dev/null
+++ b/drivers/iio/common/scmi_sensors/Kconfig

@@ -0,0 +1,18 @@
+#
+# IIO over SCMI
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "IIO SCMI Sensors"
+
+config IIO_SCMI
+     tristate "IIO SCMI"
+        depends on ARM_SCMI_PROTOCOL
+        select IIO_BUFFER
+        select IIO_KFIFO_BUF
+     help
+          Say yes here to build support for IIO SCMI Driver.
+          This provides ARM SCMI Protocol based IIO device.
+          This driver provides support for accelerometer and

gyroscope

quoted

+          sensors available on SCMI based platforms.
+endmenu

diff --git a/drivers/iio/common/scmi_sensors/Makefile

b/drivers/iio/common/scmi_sensors/Makefile

quoted

new file mode 100644
index 000000000000..f13140a2575a

--- /dev/null
+++ b/drivers/iio/common/scmi_sensors/Makefile

@@ -0,0 +1,5 @@
+# SPDX - License - Identifier : GPL - 2.0 - only
+#
+# Makefile for the IIO over SCMI
+#
+obj-$(CONFIG_IIO_SCMI) += scmi_iio.o

diff --git a/drivers/iio/common/scmi_sensors/scmi_iio.c

b/drivers/iio/common/scmi_sensors/scmi_iio.c

quoted

new file mode 100644
index 000000000000..331ffaffd06f

--- /dev/null
+++ b/drivers/iio/common/scmi_sensors/scmi_iio.c

@@ -0,0 +1,742 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * System Control and Management Interface(SCMI) based IIO sensor

driver

quoted

+ *
+ * Copyright (C) 2020 Google LLC

Probably want to include 2021 given you are still making substantial

changes ;)

quoted

+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/kfifo_buf.h>
+#include <linux/iio/sysfs.h>
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/scmi_protocol.h>
+#include <linux/time.h>
+#include <linux/types.h>
+
+#define ilog10(x) (ilog2(x) / const_ilog2(10))

That feels like it's probably not great for precision.

quoted

+#define UHZ_PER_HZ 1000000UL
+#define ODR_EXPAND(odr, uodr) (((odr) * 1000000ULL) + (uodr))

Prefix these if driver specific.
For those that aren't perhaps we can think about putting them in
generic headers.

quoted

+#define MAX_NUM_OF_CHANNELS 4
+#define H32(x) (FIELD_GET(GENMASK_ULL(63, 32), (x)))
+#define L32(x) (FIELD_GET(GENMASK_ULL(31, 0), (x)))

Can we use upper_32_bits() etc in stead of these?

quoted

+
+struct scmi_iio_priv {
+     struct scmi_handle *handle;
+     const struct scmi_sensor_info *sensor_info;
+     struct iio_dev *indio_dev;
+     long long iio_buf[MAX_NUM_OF_CHANNELS];
+     struct notifier_block sensor_update_nb;
+     u32 *freq_avail;
+     /*
+      * range_avail = [minRange resolution maxRange]
+      * with IIO val type as IIO_VAL_FRACTIONAL.
+      * Hence, array of size 6.
+      */
+     int range_avail[6];
+};
+
+static int scmi_iio_sensor_update_cb(struct notifier_block *nb,
+                                  unsigned long event, void *data)
+{
+     struct scmi_sensor_update_report *sensor_update = data;
+     struct iio_dev *scmi_iio_dev;
+     struct scmi_iio_priv *sensor;
+     s8 tstamp_scale;
+     u64 time, time_ns;
+     int i;
+
+     if (sensor_update->readings_count == 0)
+             return NOTIFY_DONE;
+
+     sensor = container_of(nb, struct scmi_iio_priv,

sensor_update_nb);

quoted

+
+     for (i = 0; i < sensor_update->readings_count; i++)
+             sensor->iio_buf[i] = sensor_update->readings[i].value;
+
+     if (!sensor->sensor_info->timestamped) {
+             time_ns = sensor_update->timestamp;
+     } else {
+             /*
+              * All the axes are supposed to have the same value

for timestamp.

quoted

+              *  We are just using the values from the Axis 0

here.

quoted

Slightly odd indenting of comment here.

quoted

+              */
+             time = sensor_update->readings[0].timestamp;
+
+             /*
+              *  Timestamp returned by SCMI is in seconds and is

equal to

quoted

+              *  time * power-of-10 multiplier(tstamp_scale)

seconds.

quoted

+              *  Converting the timestamp to nanoseconds below.
+              */
+             tstamp_scale = sensor->sensor_info->tstamp_scale +
+                               ilog10(NSEC_PER_SEC);
+             if (tstamp_scale < 0)
+                     time_ns = div64_u64(time,
+                                         int_pow(10,

abs(tstamp_scale)));

quoted

+             else
+                     time_ns = time * int_pow(10, tstamp_scale);
+     }
+
+     scmi_iio_dev = sensor->indio_dev;
+     iio_push_to_buffers_with_timestamp(scmi_iio_dev,

sensor->iio_buf,

quoted

+                                        time_ns);
+     return NOTIFY_OK;
+}
+
+static int scmi_iio_buffer_preenable(struct iio_dev *iio_dev)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     u32 sensor_id = sensor->sensor_info->id;
+     u32 sensor_config;
+     int err;
+
+     if (sensor->sensor_info->timestamped)
+             sensor_config |=

FIELD_PREP(SCMI_SENS_CFG_TSTAMP_ENABLED_MASK,

quoted

quoted
quoted
+  

 SCMI_SENS_CFG_TSTAMP_ENABLE);

quoted

+
+     sensor_config |= FIELD_PREP(SCMI_SENS_CFG_SENSOR_ENABLED_MASK,
+                                 SCMI_SENS_CFG_SENSOR_ENABLE);
+
+     err =

sensor->handle->notify_ops->register_event_notifier(sensor->handle,

quoted

+                     SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
+                     &sensor_id, &sensor->sensor_update_nb);
+     if (err) {
+             dev_err(&iio_dev->dev,
+                     "Error in registering sensor update notifier

for sensor %s err %d",

quoted

+                     sensor->sensor_info->name, err);
+             return err;
+     }
+
+     err = sensor->handle->sensor_ops->config_set(sensor->handle,
+                     sensor->sensor_info->id, sensor_config);
+     if (err) {
+

 sensor->handle->notify_ops->unregister_event_notifier(sensor->handle,

quoted

+                     SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
+                     &sensor_id, &sensor->sensor_update_nb);
+             dev_err(&iio_dev->dev, "Error in enabling sensor %s

err %d",

quoted

+                     sensor->sensor_info->name, err);
+     }
+
+     return err;
+}
+
+static int scmi_iio_buffer_postdisable(struct iio_dev *iio_dev)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     u32 sensor_id = sensor->sensor_info->id;
+     u32 sensor_config = 0;
+     int err;
+
+     sensor_config |= FIELD_PREP(SCMI_SENS_CFG_SENSOR_ENABLED_MASK,
+                                 SCMI_SENS_CFG_SENSOR_DISABLE);
+
+     err =

sensor->handle->notify_ops->unregister_event_notifier(sensor->handle,

quoted

+                     SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
+                     &sensor_id, &sensor->sensor_update_nb);
+     if (err) {
+             dev_err(&iio_dev->dev,
+                     "Error in unregistering sensor update notifier

for sensor %s err %d",

quoted

+                     sensor->sensor_info->name, err);
+             return err;
+     }
+
+     err = sensor->handle->sensor_ops->config_set(sensor->handle,

sensor_id,

quoted

+                                                  sensor_config);
+     if (err) {
+             dev_err(&iio_dev->dev,
+                     "Error in disabling sensor %s with err %d",
+                     sensor->sensor_info->name, err);
+     }
+
+     return err;
+}
+
+static const struct iio_buffer_setup_ops scmi_iio_buffer_ops = {
+     .preenable = scmi_iio_buffer_preenable,
+     .postdisable = scmi_iio_buffer_postdisable,
+};
+
+static int scmi_iio_read_avail(struct iio_dev *iio_dev,
+                            struct iio_chan_spec const *chan,
+                            const int **vals, int *type, int

*length,

quoted

+                            long mask)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+
+     switch (mask) {
+     case IIO_CHAN_INFO_SAMP_FREQ:
+             *vals = sensor->freq_avail;
+             *type = IIO_VAL_INT_PLUS_MICRO;
+             *length = sensor->sensor_info->intervals.count * 2;
+             if (sensor->sensor_info->intervals.segmented)
+                     return IIO_AVAIL_RANGE;
+             else
+                     return IIO_AVAIL_LIST;
+     case IIO_CHAN_INFO_RAW:
+             *vals = sensor->range_avail;
+             *type = IIO_VAL_FRACTIONAL;
+             *length = ARRAY_SIZE(sensor->range_avail);
+             return IIO_AVAIL_RANGE;
+     default:
+             return -EINVAL;
+     }
+}
+
+static int scmi_iio_set_odr_val(struct iio_dev *iio_dev, int val,

int val2)

quoted

+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     u64 sec, mult, uHz;
+     u32 sensor_config;
+
+     int err =

sensor->handle->sensor_ops->config_get(sensor->handle,

quoted

+                     sensor->sensor_info->id, &sensor_config);
+     if (err) {
+             dev_err(&iio_dev->dev,
+                     "Error in getting sensor config for sensor %s

err %d",

quoted

+                     sensor->sensor_info->name, err);
+             return err;
+     }
+
+     uHz = ODR_EXPAND(val, val2);
+
+     /*
+      * The seconds field in the sensor interval in SCMI is 16 bits

long

quoted

+      * Therefore seconds  = 1/Hz <= 0xFFFF. As floating point

calculations are

quoted

+      * discouraged in the kernel driver code, to calculate the

scale factor (sf)

quoted

+      * (1* 1000000 * sf)/uHz <= 0xFFFF. Therefore, sf <= (uHz *

0xFFFF)/1000000

quoted

+      */
+     mult = ilog10(((u64)uHz * 0xFFFF) / UHZ_PER_HZ);
+
+     sec = div64_u64(int_pow(10, mult) * UHZ_PER_HZ, uHz);
+     if (sec == 0) {
+             dev_err(&iio_dev->dev,
+                     "Trying to set invalid sensor update value for

sensor %s",

quoted

+                     sensor->sensor_info->name);
+             return -EINVAL;
+     }
+
+     sensor_config &= ~SCMI_SENS_CFG_UPDATE_SECS_MASK;
+     sensor_config |= FIELD_PREP(SCMI_SENS_CFG_UPDATE_SECS_MASK,

sec);

quoted

+     sensor_config &= ~SCMI_SENS_CFG_UPDATE_EXP_MASK;
+     sensor_config |= FIELD_PREP(SCMI_SENS_CFG_UPDATE_EXP_MASK,

-mult);

quoted

+
+     if (sensor->sensor_info->timestamped) {
+             sensor_config &= ~SCMI_SENS_CFG_TSTAMP_ENABLED_MASK;
+             sensor_config |=

FIELD_PREP(SCMI_SENS_CFG_TSTAMP_ENABLED_MASK,

quoted

quoted
quoted
+  

 SCMI_SENS_CFG_TSTAMP_ENABLE);

quoted

+     }
+
+     sensor_config &= ~SCMI_SENS_CFG_ROUND_MASK;
+     sensor_config |=
+             FIELD_PREP(SCMI_SENS_CFG_ROUND_MASK,

SCMI_SENS_CFG_ROUND_AUTO);

quoted

+
+     err = sensor->handle->sensor_ops->config_set(sensor->handle,
+                     sensor->sensor_info->id, sensor_config);
+     if (err)
+             dev_err(&iio_dev->dev,
+                     "Error in setting sensor update interval for

sensor %s value %u err %d",

quoted

+                     sensor->sensor_info->name, sensor_config, err);
+
+     return err;
+}
+
+static int scmi_iio_write_raw(struct iio_dev *iio_dev,
+                           struct iio_chan_spec const *chan, int

val,

quoted

+                           int val2, long mask)
+{
+     int err;
+
+     switch (mask) {
+     case IIO_CHAN_INFO_SAMP_FREQ:
+             mutex_lock(&iio_dev->mlock);
+             err = scmi_iio_set_odr_val(iio_dev, val, val2);
+             mutex_unlock(&iio_dev->mlock);
+             return err;
+     default:
+             return -EINVAL;
+     }
+}
+
+static u64 scmi_iio_convert_interval_to_ns(u32 val)
+{
+     u64 sensor_update_interval =
+             SCMI_SENS_INTVL_GET_SECS(val) * NSEC_PER_SEC;
+     u64 sensor_interval_mult;
+     int mult;
+
+     mult = SCMI_SENS_INTVL_GET_EXP(val);
+     if (mult < 0) {
+             sensor_interval_mult = int_pow(10, abs(mult));
+             sensor_update_interval =
+                     sensor_update_interval / sensor_interval_mult;
+     } else {
+             sensor_interval_mult = int_pow(10, mult);
+             sensor_update_interval =
+                     sensor_update_interval * sensor_interval_mult;
+     }
+     return sensor_update_interval;
+}
+
+static void convert_ns_to_freq(u64 interval_ns, u64 *hz, u64 *uhz)
+{
+     u64 rem;
+
+     *hz = div64_u64_rem(NSEC_PER_SEC, interval_ns, &rem);
+     *uhz = (rem * 1000000UL) / interval_ns;
+}
+
+static int scmi_iio_get_odr_val(struct iio_dev *iio_dev, int *val,

int *val2)

quoted

+{
+     u64 sensor_update_interval, sensor_interval_mult, hz, uhz;
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     u32 sensor_config;
+     int mult;
+
+     int err =

sensor->handle->sensor_ops->config_get(sensor->handle,

quoted

+                     sensor->sensor_info->id, &sensor_config);
+     if (err) {
+             dev_err(&iio_dev->dev,
+                     "Error in getting sensor config for sensor %s

err %d",

quoted

+                     sensor->sensor_info->name, err);
+             return err;
+     }
+
+     sensor_update_interval =
+             SCMI_SENS_CFG_GET_UPDATE_SECS(sensor_config) *

NSEC_PER_SEC;

quoted

+
+     mult = SCMI_SENS_CFG_GET_UPDATE_EXP(sensor_config);
+     if (mult < 0) {
+             sensor_interval_mult = int_pow(10, abs(mult));
+             sensor_update_interval =
+                     sensor_update_interval / sensor_interval_mult;
+     } else {
+             sensor_interval_mult = int_pow(10, mult);
+             sensor_update_interval =
+                     sensor_update_interval * sensor_interval_mult;
+     }
+
+     convert_ns_to_freq(sensor_update_interval, &hz, &uhz);
+     *val = hz;
+     *val2 = uhz;
+     return 0;
+}
+
+static int scmi_iio_read_raw(struct iio_dev *iio_dev,
+                          struct iio_chan_spec const *ch, int *val,
+                          int *val2, long mask)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     s8 scale;
+     int ret;
+
+     switch (mask) {
+     case IIO_CHAN_INFO_SCALE:
+             scale =

sensor->sensor_info->axis[ch->scan_index].scale;

quoted

+             if (scale < 0) {
+                     *val = 1;
+                     *val2 = int_pow(10, abs(scale));
+                     return IIO_VAL_FRACTIONAL;
+             }
+             *val = int_pow(10, scale);
+             return IIO_VAL_INT;
+     case IIO_CHAN_INFO_SAMP_FREQ:
+             ret = scmi_iio_get_odr_val(iio_dev, val, val2);
+             return ret ? ret : IIO_VAL_INT_PLUS_MICRO;
+     default:
+             return -EINVAL;
+     }
+}
+
+static const struct iio_info scmi_iio_info = {
+     .read_raw = scmi_iio_read_raw,
+     .read_avail = scmi_iio_read_avail,
+     .write_raw = scmi_iio_write_raw,
+};
+
+static void scmi_iio_set_timestamp_channel(struct iio_chan_spec

*iio_chan,

quoted

+                                        int scan_index)
+{
+     iio_chan->type = IIO_TIMESTAMP;
+     iio_chan->channel = -1;
+     iio_chan->scan_index = scan_index;
+     iio_chan->scan_type.sign = 'u';
+     iio_chan->scan_type.realbits = 64;
+     iio_chan->scan_type.storagebits = 64;
+}
+
+static void scmi_iio_set_data_channel(struct iio_chan_spec

*iio_chan,

quoted

+                                   enum iio_chan_type type,
+                                   enum iio_modifier mod, int

scan_index)

quoted

+{
+     iio_chan->type = type;
+     iio_chan->modified = 1;
+     iio_chan->channel2 = mod;
+     iio_chan->info_mask_separate = BIT(IIO_CHAN_INFO_SCALE);
+     iio_chan->info_mask_shared_by_type =

BIT(IIO_CHAN_INFO_SAMP_FREQ);

quoted

+     iio_chan->info_mask_shared_by_type_available =
+             BIT(IIO_CHAN_INFO_SAMP_FREQ) | BIT(IIO_CHAN_INFO_RAW);
+     iio_chan->scan_index = scan_index;
+     iio_chan->scan_type.sign = 's';
+     iio_chan->scan_type.realbits = 64;
+     iio_chan->scan_type.storagebits = 64;
+     iio_chan->scan_type.endianness = IIO_LE;
+}
+
+static int scmi_iio_get_chan_modifier(const char *name,
+                                   enum iio_modifier *modifier)
+{
+     char *pch, mod;
+
+     if (!name)
+             return -EINVAL;
+
+     pch = strrchr(name, '_');
+     if (!pch)
+             return -EINVAL;
+
+     mod = *(pch + 1);
+     switch (mod) {
+     case 'X':
+             *modifier = IIO_MOD_X;
+             return 0;
+     case 'Y':
+             *modifier = IIO_MOD_Y;
+             return 0;
+     case 'Z':
+             *modifier = IIO_MOD_Z;
+             return 0;
+     default:
+             return -EINVAL;
+     }
+}
+
+static int scmi_iio_get_chan_type(u8 scmi_type, enum iio_chan_type

*iio_type)

quoted

+{
+     switch (scmi_type) {
+     case METERS_SEC_SQUARED:
+             *iio_type = IIO_ACCEL;
+             return 0;
+     case RADIANS_SEC:
+             *iio_type = IIO_ANGL_VEL;
+             return 0;
+     default:
+             return -EINVAL;
+     }
+}
+
+static int scmi_iio_get_sensor_max_range(struct iio_dev *iio_dev,

int *val,

quoted

+                                      int *val2)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     int max_range_high, max_range_low;
+     long long max_range;
+
+     /*
+      * All the axes are supposed to have the same value for max

range.

quoted

+      * We are just using the values from the Axis 0 here.
+      */
+     if (sensor->sensor_info->axis[0].extended_attrs) {
+             max_range =

sensor->sensor_info->axis[0].attrs.max_range;

quoted

+             max_range_high = H32(max_range);
+             max_range_low = L32(max_range);
+
+             /*
+              * As IIO Val types have no provision for 64 bit

values,

quoted

+              * this driver only supports sensors whose maximum

range

quoted

+              * reported by the SCMI Platform fits within lower 32

bits

quoted

+              */
+             if (max_range_high != 0)
+                     return -EINVAL;
+
+             *val = max_range_low;
+             *val2 = 1;
+     }
+     return 0;
+}
+
+static void scmi_iio_get_sensor_resolution(struct iio_dev *iio_dev,

int *val,

quoted

+                                        int *val2)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+
+     /*
+      * All the axes are supposed to have the same value for

resolution

quoted

+      * and exponent. We are just using the values from the Axis 0

here.

quoted

+      */
+     if (sensor->sensor_info->axis[0].extended_attrs) {
+             uint resolution =

sensor->sensor_info->axis[0].resolution;

quoted

+             s8 exponent = sensor->sensor_info->axis[0].exponent;
+             s8 scale = sensor->sensor_info->axis[0].scale;
+
+             /*
+              * To provide the raw value for the resolution to the

userspace,

quoted

+              * need to divide the resolution exponent by the

sensor scale

quoted

+              */
+             exponent = exponent - scale;
+             if (exponent >= 0) {
+                     *val = resolution * int_pow(10, exponent);
+                     *val2 = 1;
+             } else {
+                     *val = resolution;
+                     *val2 = int_pow(10, abs(exponent));
+             }
+     }
+}
+
+static int scmi_iio_get_sensor_min_range(struct iio_dev *iio_dev,

int *val,

quoted

+                                      int *val2)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     int min_range_high, min_range_low;
+     long long min_range;
+
+     /*
+      * All the axes are supposed to have the same value for min

range.

quoted

+      * We are just using the values from the Axis 0 here.
+      */
+     if (sensor->sensor_info->axis[0].extended_attrs) {
+             min_range =

sensor->sensor_info->axis[0].attrs.min_range;

quoted

+             min_range_high = H32(min_range);
+             min_range_low = L32(min_range);
+
+             /*
+              * As IIO Val types have no provision for 64 bit

values,

quoted

+              * this driver only supports sensors whose minimum

range

quoted

+              * reported by SCMI Platform fits within lower 32 bits
+              */

As discussed in previous thread (after you sent this!) perhaps we just
need to do the maths in here rather than rely on core handling of

IIO_VAL_FRACTIONAL.

quoted

That would give us a greater potential range.  There may still be

values

quoted

we can't represent, but it should be less restrictive that this
assumption. (pity as this was neater!)

quoted

+             if (min_range_high != 0xFFFFFFFF)
+                     return -EINVAL;
+
+             *val = min_range_low;
+             *val2 = 1;
+     }
+     return 0;
+}
+
+static int scmi_iio_set_sensor_range_avail(struct iio_dev *iio_dev)
+{
+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     int ret;
+
+     ret = scmi_iio_get_sensor_min_range(iio_dev,

&sensor->range_avail[0],

quoted

+                                         &sensor->range_avail[1]);
+     if (ret)
+             return ret;
+
+     scmi_iio_get_sensor_resolution(iio_dev,

&sensor->range_avail[2],

quoted

+                                    &sensor->range_avail[3]);
+     ret = scmi_iio_get_sensor_max_range(iio_dev,

&sensor->range_avail[4],

quoted

+                                         &sensor->range_avail[5]);
+     return ret;
+}
+
+static int scmi_iio_set_sampling_freq_avail(struct iio_dev *iio_dev)
+{
+     u64 cur_interval_ns, low_interval_ns, high_interval_ns,

step_size_ns,

quoted

+             hz, uhz;
+     unsigned int cur_interval, low_interval, high_interval,

step_size;

quoted

+     struct scmi_iio_priv *sensor = iio_priv(iio_dev);
+     int i;
+
+     sensor->freq_avail = devm_kzalloc(&iio_dev->dev,
+                                       sizeof(u32) *

(sensor->sensor_info->intervals.count * 2),

quoted

Slight preference for sizeof(*sensor->freq_avail) *...
as saves reviewer having to go check types match up.

quoted

+                                       GFP_KERNEL);
+     if (!sensor->freq_avail)
+             return -ENOMEM;
+
+     if (sensor->sensor_info->intervals.segmented) {
+             low_interval = sensor->sensor_info->intervals
+

.desc[SCMI_SENS_INTVL_SEGMENT_LOW];

quoted

+             low_interval_ns =

scmi_iio_convert_interval_to_ns(low_interval);

quoted

+             convert_ns_to_freq(low_interval_ns, &hz, &uhz);
+             sensor->freq_avail[0] = hz;
+             sensor->freq_avail[1] = uhz;
+
+             step_size = sensor->sensor_info->intervals
+

 .desc[SCMI_SENS_INTVL_SEGMENT_STEP];

quoted

+             step_size_ns =

scmi_iio_convert_interval_to_ns(step_size);

quoted

+             convert_ns_to_freq(step_size_ns, &hz, &uhz);
+             sensor->freq_avail[2] = hz;
+             sensor->freq_avail[3] = uhz;
+
+             high_interval = sensor->sensor_info->intervals
+

 .desc[SCMI_SENS_INTVL_SEGMENT_HIGH];

quoted

+             high_interval_ns =
+                     scmi_iio_convert_interval_to_ns(high_interval);
+             convert_ns_to_freq(high_interval_ns, &hz, &uhz);
+             sensor->freq_avail[4] = hz;
+             sensor->freq_avail[5] = uhz;
+     } else {
+             for (i = 0; i < sensor->sensor_info->intervals.count;

i++) {

quoted

+                     cur_interval =

sensor->sensor_info->intervals.desc[i];

quoted

+                     cur_interval_ns =

scmi_iio_convert_interval_to_ns(cur_interval);

quoted

+                     convert_ns_to_freq(cur_interval_ns, &hz, &uhz);
+                     sensor->freq_avail[i * 2] = hz;
+                     sensor->freq_avail[i * 2 + 1] = uhz;
+             }
+     }
+     return 0;
+}
+
+static int scmi_iio_buffers_setup(struct iio_dev *scmi_iiodev)
+{
+     struct iio_buffer *buffer;
+
+     buffer = devm_iio_kfifo_allocate(&scmi_iiodev->dev);
+     if (!buffer)
+             return -ENOMEM;
+
+     iio_device_attach_buffer(scmi_iiodev, buffer);
+     scmi_iiodev->modes |= INDIO_BUFFER_SOFTWARE;
+     scmi_iiodev->setup_ops = &scmi_iio_buffer_ops;
+     return 0;
+}
+
+static int scmi_alloc_iiodev(struct device *dev, struct scmi_handle

*handle,

quoted

+                          const struct scmi_sensor_info

*sensor_info,

quoted

+                          struct iio_dev **scmi_iio_dev)

Perhaps it would be nice to use PTR_ERR etc and have this function

just return

quoted

the struct iio_dev.   That would fit with more common form for

allocation functions.

quoted

+{
+     struct iio_chan_spec *iio_channels;
+     struct scmi_iio_priv *sensor;
+     enum iio_modifier modifier;
+     enum iio_chan_type type;
+     struct iio_dev *iiodev;
+     int i, ret;
+
+     iiodev = devm_iio_device_alloc(dev, sizeof(*sensor));
+     if (!iiodev)
+             return -ENOMEM;
+
+     iiodev->modes = INDIO_DIRECT_MODE;
+     iiodev->dev.parent = dev;
+     sensor = iio_priv(iiodev);
+     sensor->handle = handle;
+     sensor->sensor_info = sensor_info;
+     sensor->sensor_update_nb.notifier_call =

scmi_iio_sensor_update_cb;

quoted

+     sensor->indio_dev = iiodev;
+
+     /* adding one additional channel for timestamp */
+     iiodev->num_channels = sensor_info->num_axis + 1;
+     iiodev->name = sensor_info->name;
+     iiodev->info = &scmi_iio_info;
+
+     iio_channels =
+             devm_kzalloc(dev,
+                          sizeof(*iio_channels) *

(iiodev->num_channels),

quoted

+                          GFP_KERNEL);
+     if (!iio_channels)
+             return -ENOMEM;
+
+     scmi_iio_set_sampling_freq_avail(iiodev);
+
+     ret = scmi_iio_set_sensor_range_avail(iiodev);
+     if (ret) {
+             dev_err(dev, "Error while setting the sensor %s range

%d",

quoted

+                     sensor_info->name, ret);
+             return ret;
+     }
+
+     for (i = 0; i < sensor_info->num_axis; i++) {
+             ret =

scmi_iio_get_chan_type(sensor_info->axis[i].type, &type);

quoted

+             if (ret < 0)
+                     return ret;
+
+             ret =

scmi_iio_get_chan_modifier(sensor_info->axis[i].name,

quoted

+                                              &modifier);
+             if (ret < 0)
+                     return ret;
+
+             scmi_iio_set_data_channel(&iio_channels[i], type,

modifier,

quoted

+                                       sensor_info->axis[i].id);
+     }
+
+     scmi_iio_set_timestamp_channel(&iio_channels[i], i);
+     iiodev->channels = iio_channels;
+     *scmi_iio_dev = iiodev;
+     return ret;
+}
+
+static int scmi_iio_dev_probe(struct scmi_device *sdev)
+{
+     const struct scmi_sensor_info *sensor_info;
+     struct scmi_handle *handle = sdev->handle;
+     struct device *dev = &sdev->dev;
+     struct iio_dev *scmi_iio_dev;
+     u16 nr_sensors;
+     int err, i;
+
+     if (!handle || !handle->sensor_ops) {
+             dev_err(dev, "SCMI device has no sensor

interface\n");

quoted

I'm going to guess we can't actually get here because the registration
would't have happened if either of those are true?
If so perhaps drop the error message.

quoted

+             return -EINVAL;
+     }
+
+     nr_sensors = handle->sensor_ops->count_get(handle);
+     if (!nr_sensors) {
+             dev_dbg(dev, "0 sensors found via SCMI bus\n");

-ENODEV maybe?

quoted

+             return -EINVAL;
+     }
+
+     dev_dbg(dev, "%d sensors found via SCMI bus\n", nr_sensors);

Clear out any debug prints out that don't provide info that can't be

obtained

quoted

farily easily from elsewhere.  In this case they will either be

registered

quoted

or not and we'll get error messages.
These sort of prints bitrot over time so we want to limit them to the

truely

quoted

useful.

quoted

+
+     for (i = 0; i < nr_sensors; i++) {
+             sensor_info = handle->sensor_ops->info_get(handle, i);
+             if (!sensor_info) {
+                     dev_err(dev, "SCMI sensor %d has missing

info\n", i);

quoted

+                     return -EINVAL;
+             }
+
+             /* Skipping scalar sensor,as this driver only supports

accel and gyro */

quoted

+             if (sensor_info->num_axis == 0)
+                     continue;

So there is a situation where this driver never creates anything?  In

that path I'd

quoted

like to see an -ENODEV error return.

quoted

+
+             err = scmi_alloc_iiodev(dev, handle, sensor_info,
+                                     &scmi_iio_dev);
+             if (err < 0) {
+                     dev_err(dev,
+                             "failed to allocate IIO device for

sensor %s: %d\n",

quoted

+                             sensor_info->name, err);
+                     return err;
+             }
+
+             err = scmi_iio_buffers_setup(scmi_iio_dev);
+             if (err < 0) {
+                     dev_err(dev,
+                             "IIO buffer setup error at sensor %s:

%d\n",

quoted

+                             sensor_info->name, err);
+                     return err;
+             }
+
+             err = devm_iio_device_register(dev, scmi_iio_dev);
+             if (err) {
+                     dev_err(dev,
+                             "IIO device registration failed at

sensor %s: %d\n",

quoted

+                             sensor_info->name, err);
+                     return err;
+             }
+     }
+     return err;
+}
+
+static const struct scmi_device_id scmi_id_table[] = {
+     { SCMI_PROTOCOL_SENSOR, "iiodev" },

I'm curious on this.  What actually causes a match on that
iiodev?  From digging around the scmi core am I right in thinking
that this iiodev id needs to be explicitly listed?

It would be good to include any changes needed there in this
series.

quoted

+     {},
+};
+
+MODULE_DEVICE_TABLE(scmi, scmi_id_table);
+
+static struct scmi_driver scmi_iiodev_driver = {
+     .name = "scmi-sensor-iiodev",
+     .probe = scmi_iio_dev_probe,
+     .id_table = scmi_id_table,
+};
+
+module_scmi_driver(scmi_iiodev_driver);
+
+MODULE_AUTHOR("Jyoti Bhayana [off-list ref]");
+MODULE_DESCRIPTION("SCMI IIO Driver");
+MODULE_LICENSE("GPL v2");

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