linux-kernel - Re: [PATCH v5 1/3] dt-bindings:iio:adc: add generic settling-time-us and oversampling-ratio channel properties

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Date:   Mon, 29 Mar 2021 15:06:20 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>,
        Robin van der Gracht <robin@...tonic.nl>,
        linux-iio@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH v5 1/3] dt-bindings:iio:adc: add generic settling-time-us
 and oversampling-ratio channel properties

On Mon, Mar 29, 2021 at 11:25:32AM +0100, Jonathan Cameron wrote:
> On Mon, 29 Mar 2021 09:31:29 +0200
> Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> 
> > Settling time and over sampling is a typical challenge for different IIO ADC
> > devices. So, introduce channel specific settling-time-us and oversampling-ratio
> > properties to cover this use case.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> >  Documentation/devicetree/bindings/iio/adc/adc.yaml | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> > index 912a7635edc4..d5bc86d2a2af 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> > @@ -39,4 +39,12 @@ properties:
> >        The first value specifies the positive input pin, the second
> >        specifies the negative input pin.
> >  
> > +  settling-time-us:
> > +    description:
> > +      Time between enabling the channel and firs stable readings.
> 
> first

ack

> > +
> > +  oversampling-ratio:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: Number of data samples which are averaged for each read.
> 
> I think I've asked about this in previous reviews, but I want a clear statement
> of why you think this property is a feature of the 'board' (and hence should be
> in device tree) rather than setting sensible defaults and leaving any control
> to userspace?

yes, my reply was:
> Oversampling is used as replacement of or addition to the low-pass filter. The
> filter can be implemented on board, but it will change settling time
> characteristic. Since low-pass filter is board specific characteristic, this
> property belongs in device tree as well.

I could imagine that this values can be overwritten from user space for
diagnostic, but we need some working default values. 

Should I integrate this comment in to the yaml?

Regards,
Oleksij
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