Re: [PATCH 2/3] dt-bindings: iio: adc: stm32: add optional min-sample-time

Fabrice Gasnier
2017-07-24T07:56:38Z

On 07/23/2017 12:53 PM, Jonathan Cameron wrote:
> On Tue, 18 Jul 2017 14:35:31 +0200
> Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
>
>> STM32 ADC allows each channel to be sampled with a different sampling
>> time. There's an application note that deals with this: 'How to get
>> the best ADC accuracy in STM32...' It basically depends on analog input
>> signal electrical properties (depends on board).
>>
>> Add optional 'min-sample-time' property so this can be tuned in dt.
>>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
>
> This isn't yet very standard, so I think it needs a manufacturer
> prefix, e.g. st,min-sample-time. Also convention is I believe
> to include the units as part of the naming where appropriate.
>
> Hence st,min-sample-time-nsecs

Hi Jonathan,

I originally used st,... form, when writing this patch, until I found
out there's 'min-sample-time' in vf610 adc dt-bindings:
- Documentation/devicetree/bindings/iio/adc/vf610-adc.txt
It looks like to me very similar.

I also agree it misses '-nsecs' units. Sure, I can use your suggestion
above...

Please can you just confirm if I should use same property as vf610 adc,
or 'st,min-sample-time-nsecs' ?

Thanks for reviewing,
Best regards,
Fabrice

>
> Otherwise, seems good to me.
>
> Jonathan
>> ---
>> Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>> index 8310073..9cd964b 100644
>> --- a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>> +++ b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>> @@ -74,6 +74,11 @@ Optional properties:
>> * can be 6, 8, 10 or 12 on stm32f4
>> * can be 8, 10, 12, 14 or 16 on stm32h7
>> Default is maximum resolution if unset.
>> +- min-sample-time: Minimum sampling time in nanoseconds.
>> + Depending on hardware (board) e.g. high/low analog input source impedance,
>> + fine tune of ADC sampling time may be recommended.
>> + This can be either one value or an array that matches 'st,adc-channels' list,
>> + to set sample time resp. for all channels, or independently for each channel.
>>
>> Example:
>> adc: adc@40012000 {
>