On Mon, 23 Oct 2017 10:06:27 +0200
Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote:
> On 10/21/2017 09:23 PM, Jonathan Cameron wrote:
> > On Sat, 21 Oct 2017 18:54:01 +0100
> > Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> >
> >> On Tue, 17 Oct 2017 15:15:43 +0200
> >> Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote:
> >>
> >>> 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 <fabrice.gasnier@xxxxxx>
> >> 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 ?
>
> >
> > 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
>
> >
> > Thanks,
> >
> > Jonathan
> >>
> >> Jonathan
> >>
> >>> ---
> >>> 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
> >>>
> >>
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