linux-kernel - Re: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add calibration properties

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Message-ID: <20250713160247.0f22bbfe@jic23-huawei>
Date: Sun, 13 Jul 2025 16:02:47 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Primoz Fiser <primoz.fiser@...ik.com>, Haibo Chen <haibo.chen@....com>,
 Nuno Sa <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Rob
 Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
 <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, linux-iio@...r.kernel.org,
 imx@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 upstream@...ts.phytec.de, andrej.picej@...ik.com
Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add calibration
 properties

On Thu, 10 Jul 2025 10:46:44 -0500
David Lechner <dlechner@...libre.com> wrote:

> On 7/10/25 2:39 AM, Primoz Fiser wrote:
> > From: Andrej Picej <andrej.picej@...ik.com>
> > 
> > Document i.MX93 ADC calibration properties and how to set them.
> > 
> > Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
> > Signed-off-by: Primoz Fiser <primoz.fiser@...ik.com>
> > ---
> >  .../bindings/iio/adc/nxp,imx93-adc.yaml       | 21 +++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
> > index c2e5ff418920..d1c04cf85fe6 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
> > @@ -52,6 +52,27 @@ properties:
> >    "#io-channel-cells":
> >      const: 1
> >  
> > +  nxp,calib-avg-en:
> > +    default: 1
> > +    description:
> > +      Enable or disable calibration averaging function (AVGEN).
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [ 0, 1 ]
> > +
> > +  nxp,calib-nr-samples:
> > +    default: 512
> > +    description:
> > +      Selects number of samples (NRSMPL) to be used during calibration.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [ 16, 32, 128, 512 ]

Allow 1 as a value and drop the enabled above.   Averaging over 1 sample
is same as no averaging and gives simpler binding.

> > +
> > +  nxp,calib-t-sample:
> > +    default: 22
> > +    description:
> > +      Selects sample time (TSAMP) of calibration conversions in ADC clock cycles
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [ 8, 16, 22, 32 ]
> > +
> >  required:
> >    - compatible
> >    - reg  
> 
> This seem like things that should be set at runtime rather than
> in the devicetree. Unless there is some justification on why
> these values depend on how the chip is wired up?

Further to that, I'd like to see some explanation of why we care
to change it at all. Is it ever a bad idea to enable averaging and
pick a large number of samples for calibration?

> 
>