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

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Date:   Mon, 24 Jul 2017 23:04:18 +0800
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
CC:     Jonathan Cameron <jic23@...nel.org>, <mark.rutland@....com>,
        <devicetree@...r.kernel.org>, <benjamin.gaignard@...aro.org>,
        <lars@...afoo.de>, <alexandre.torgue@...com>,
        <linux-iio@...r.kernel.org>, <pmeerw@...erw.net>,
        <linux@...linux.org.uk>, <linux-kernel@...r.kernel.org>,
        <robh+dt@...nel.org>, <mcoquelin.stm32@...il.com>,
        <knaack.h@....de>, <linux-arm-kernel@...ts.infradead.org>,
        <benjamin.gaignard@...com>
Subject: Re: [PATCH 2/3] dt-bindings: iio: adc: stm32: add optional
 min-sample-time

On Mon, 24 Jul 2017 09:55:37 +0200
Fabrice Gasnier <fabrice.gasnier@...com> wrote:

> 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' ?
st,min-sample-time-nsecs.

We might well add a generic option in future, but the burden of
supporting this old one will be trivial anyway so not a problem.

Jonathan
> 
> 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 {  
> >   
> 
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