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

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Message-ID: <81cabf83-689c-277a-5cf9-510df5cc9045@st.com>
Date:   Mon, 24 Jul 2017 09:55:37 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     <robh+dt@...nel.org>, <linux@...linux.org.uk>,
        <mark.rutland@....com>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...com>, <lars@...afoo.de>, <knaack.h@....de>,
        <pmeerw@...erw.net>, <benjamin.gaignard@...aro.org>,
        <benjamin.gaignard@...com>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] dt-bindings: iio: adc: stm32: add optional
 min-sample-time

On 07/23/2017 12:53 PM, Jonathan Cameron wrote:
> On Tue, 18 Jul 2017 14:35:31 +0200
> Fabrice Gasnier <fabrice.gasnier@...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@...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@...12000 {
>