Re: [PATCH 1/3] dt-bindings: iio: adc: stm32: add support for diff channels

On Mon, 23 Oct 2017 10:06:27 +0200
Fabrice Gasnier [off-list ref] wrote:

On 10/21/2017 09:23 PM, Jonathan Cameron wrote:

quoted

On Sat, 21 Oct 2017 18:54:01 +0100
Jonathan Cameron [off-list ref] wrote:
  

quoted

On Tue, 17 Oct 2017 15:15:43 +0200
Fabrice Gasnier [off-list ref] wrote:
 

quoted

STM32H7 ADC channels may be configured either as single-ended or
differential.
Add 'st,adc-diff-channels' property to support differential channels.
Differential channels are defined as a pair of positive and negative
inputs: vinp & vinn.

Signed-off-by: Fabrice Gasnier <redacted>    

Hmm. Fair enough.  Sometimes we support both types of channels
and leave it to userspace, but in many cases that makes little sense
- particularly if like I think is going on here, we aren't combining channels
that can be separately read but rather the negative pin is simply unused
when we are in single channel mode... (did I understand that right?)  

I clearly didn't understand.  This is same as other devices
in that we are picking a pair from the channels that can otherwise be
used as single end channels. (I think).   

Hi Jonathan,

Indeed, we're picking a pair from the channels that can be used as
single channels otherwise.
Also, it doesn't makes sense to leave the choice to userspace: when
these channels are used in differential mode, both input should be
biased. This is quite dependent on hardware (board), not really a
runtime choice.
Hope this clarifies ?

quoted

For this binding I think I'd like to see an example added showing how
this works...  

You're right, I should have added that. Please let me know if I can add
bellow example in v2:

Looks good to me.

Jonathan

Example to setup differential channels 1, 2 & 3 (with resp. 0, 6 & 7
negative inputs):
	adc: adc@40022000 {
		compatible = "st,stm32h7-adc-core";
		...
		adc1: adc@0 {
			compatible = "st,stm32h7-adc";
			...
			st,adc-diff-channels = <1 0>, <2 6>, <3 7>;
		};
	};

Thanks for reviewing,
Best Regards,
Fabrice

quoted

Thanks,

Jonathan  

quoted

Jonathan
 

quoted

---
 Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
index 48bfcaa3..c3c8de1 100644
--- a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
+++ b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt

@@ -62,6 +62,12 @@ Required properties:
 - st,adc-channels: List of single-ended channels muxed for this ADC.
   It can have up to 16 channels on stm32f4 or 20 channels on stm32h7, numbered
   from 0 to 15 or 19 (resp. for in0..in15 or in0..in19).
+- st,adc-diff-channels: List of differential channels muxed for this ADC.
+  Depending on part used, some channels can be configured as differential
+  instead of single-ended (e.g. stm32h7). List here positive and negative
+  inputs pairs as <vinp vinn>, <vinp vinn>,... vinp and vinn are numbered
+  from 0 to 19 on stm32h7)
+  Note: At least one of "st,adc-channels" or "st,adc-diff-channels" is required.
 - #io-channel-cells = <1>: See the IIO bindings section "IIO consumers" in
   Documentation/devicetree/bindings/iio/iio-bindings.txt
     

--
To unsubscribe from this list: send the line "unsubscribe linux-iio" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html  

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel