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

Message ID 1508246145-19417-2-git-send-email-fabrice.gasnier@st.com
State New
Headers show

Commit Message

Fabrice Gasnier Oct. 17, 2017, 1:15 p.m. UTC
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@st.com>
---
 Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Jonathan Cameron Oct. 21, 2017, 5:54 p.m. UTC | #1
On Tue, 17 Oct 2017 15:15:43 +0200
Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>
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?)

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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Jonathan Cameron Oct. 21, 2017, 5:55 p.m. UTC | #2
On Sat, 21 Oct 2017 18:54:01 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> On Tue, 17 Oct 2017 15:15:43 +0200
> Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>
> 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?)
> 
Forgot to say - I would ideally like a devicetree maintainer review on this
one as it's a bit unusual!

> 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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Jonathan Cameron Oct. 21, 2017, 7:23 p.m. UTC | #3
On Sat, 21 Oct 2017 18:54:01 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> On Tue, 17 Oct 2017 15:15:43 +0200
> Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>  
> 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). 

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

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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Fabrice Gasnier Oct. 23, 2017, 8:06 a.m. UTC | #4
On 10/21/2017 09:23 PM, Jonathan Cameron wrote:
> On Sat, 21 Oct 2017 18:54:01 +0100
> Jonathan Cameron <jic23@kernel.org> wrote:
> 
>> On Tue, 17 Oct 2017 15:15:43 +0200
>> Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>  
>> 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:

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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Jonathan Cameron Oct. 23, 2017, 1:09 p.m. UTC | #5
On Mon, 23 Oct 2017 10:06:27 +0200
Fabrice Gasnier <fabrice.gasnier@st.com> wrote:

> On 10/21/2017 09:23 PM, Jonathan Cameron wrote:
> > On Sat, 21 Oct 2017 18:54:01 +0100
> > Jonathan Cameron <jic23@kernel.org> wrote:
> >   
> >> On Tue, 17 Oct 2017 15:15:43 +0200
> >> Fabrice Gasnier <fabrice.gasnier@st.com> 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@st.com>    
> >> 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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> >> the body of a message to majordomo@vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html  
> >   
> 
> _______________________________________________
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Rob Herring Oct. 24, 2017, 4:41 p.m. UTC | #6
On Tue, Oct 17, 2017 at 03:15:43PM +0200, Fabrice Gasnier 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@st.com>
> ---
>  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.

Wouldn't both present be invalid?

>  - #io-channel-cells = <1>: See the IIO bindings section "IIO consumers" in
>    Documentation/devicetree/bindings/iio/iio-bindings.txt
>  
> -- 
> 1.9.1
> 
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Jonathan Cameron Oct. 24, 2017, 6:42 p.m. UTC | #7
On 24 October 2017 17:41:38 BST, Rob Herring <robh@kernel.org> wrote:
>On Tue, Oct 17, 2017 at 03:15:43PM +0200, Fabrice Gasnier 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@st.com>
>> ---
>>  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.
>
>Wouldn't both present be invalid?
>

Probably invalid to have a number in both but some channels in each would be fine.

>>  - #io-channel-cells = <1>: See the IIO bindings section "IIO
>consumers" in
>>    Documentation/devicetree/bindings/iio/iio-bindings.txt
>>  
>> -- 
>> 1.9.1
>>
Fabrice Gasnier Oct. 25, 2017, 8:05 a.m. UTC | #8
On 10/24/2017 08:42 PM, Jonathan Cameron wrote:
> 
> 
> On 24 October 2017 17:41:38 BST, Rob Herring <robh@kernel.org> wrote:
>> On Tue, Oct 17, 2017 at 03:15:43PM +0200, Fabrice Gasnier 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@st.com>
>>> ---
>>>  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.
>>
>> Wouldn't both present be invalid?
>>
> 
Hi Rob, Jonathan,

> Probably invalid to have a number in both but some channels in each would be fine.

Yes, both properties can be used together. Some channels can be used as
single-ended and some other ones as differential (mixed). But channels
can't be configured both as single-ended and differential (invalid).

I'll mention this in the note, and also update differential channels
example:

Example to setup:
- channel 1 as single-ended
- channels 2 & 3 as differential (with resp. 6 & 7 negative inputs)

	adc: adc@40022000 {
		compatible = "st,stm32h7-adc-core";
		...
		adc1: adc@0 {
			compatible = "st,stm32h7-adc";
			...
			st,adc-channels = <1>;
			st,adc-diff-channels = <2 6>, <3 7>;
		};
	};

I will send V2 with these updates.

Thanks,
Best Regards,
Fabrice
> 
>>>  - #io-channel-cells = <1>: See the IIO bindings section "IIO
>> consumers" in
>>>    Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>  
>>> -- 
>>> 1.9.1
>>>
> 
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Patch
diff mbox

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