linux-kernel - Re: [PATCH v2 2/3] dt-bindings: iio: io-channel-mux: Add property for settle time

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Date:   Fri, 8 Oct 2021 17:27:34 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Rob Herring <robh@...nel.org>
Cc:     kernel <kernel@...s.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] dt-bindings: iio: io-channel-mux: Add property for
 settle time

On 2021-10-08 15:56, Vincent Whitchurch wrote:
> On Fri, Oct 08, 2021 at 04:46:12AM +0200, Rob Herring wrote:
>> On Thu, 07 Oct 2021 15:46:40 +0200, Vincent Whitchurch wrote:
>>> Hardware may require some time for the muxed analog signals to settle
>>> after the muxing is changed.  Allow this time to be specified in the
>>> devicetree.
>>>
>>> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
>>> ---
>>>  .../devicetree/bindings/iio/multiplexer/io-channel-mux.yaml  | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>
>> Running 'make dtbs_check' with the schema in this patch gives the
>> following warnings. Consider if they are expected or the schema is
>> incorrect. These may not be new warnings.
> 
> Yes, these are not new warnings.
> 
>> Note that it is not yet a requirement to have 0 warnings for dtbs_check.
>> This will change in the future.
>>
>> Full log is available here: https://patchwork.ozlabs.org/patch/1537724
>>
>>
>> adc0mux: '#io-channel-cells' does not match any of the regexes: 'pinctrl-[0-9]+'
>> 	arch/arm/boot/dts/aspeed-bmc-ampere-mtjade.dt.yaml
>>
>> adc10mux: '#io-channel-cells' does not match any of the regexes: 'pinctrl-[0-9]+'
>> 	arch/arm/boot/dts/aspeed-bmc-ampere-mtjade.dt.yaml
> [...]
> 
> I think the fix for these is to add a "#io-channel-cells": const 1 to
> the schema.

Agreed.

>> envelope-detector-mux: channels: ['', '', 'sync-1', 'in', 'out', 'sync-2', 'sys-reg', 'ana-reg'] has non-unique elements
>> 	arch/arm/boot/dts/at91-tse850-3.dt.yaml
> 
> This one looks like an error in that particular devicetree.
> 
The double '' is intentional; this mux is 8-way but only 6 legs are
connected, with the first two unused. I don't know how or where to make
changes to dodge the warning. I don't want to put names on things that
do not exist, and the iio-mux driver is using empty names as a hint to
not configure any child channel for those indices that have empty names.
If e.g. channels 0-5 are in use, then this is not a problem since you
can just end early with 6 names instead of 8, but alas, channels 2-7
was what the hw-crowd fancied in this case.

Cheers,
Peter