linux-kernel - Re: [PATCH] iio: industrialio-core: look for aliases to request device index

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Message-ID: <Zd7hSOw3_zosyrn3@atmark-techno.com>
Date: Wed, 28 Feb 2024 16:31:20 +0900
From: Dominique Martinet <dominique.martinet@...ark-techno.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Syunya Ohshio <syunya.ohshio@...ark-techno.com>,
	Guido Günther <agx@...xcpu.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: industrialio-core: look for aliases to request
 device index

Krzysztof Kozlowski wrote on Wed, Feb 28, 2024 at 08:16:03AM +0100:
> On 28/02/2024 06:12, Dominique Martinet wrote:
> > From: Syunya Ohshio <syunya.ohshio@...ark-techno.com>
> > 
> > When using dtb overlays it can be difficult to predict which iio device
> > will get assigned what index, and there is no easy way to create
> > symlinks for /sys nodes through udev so to simplify userspace code make
> > it possible to request fixed indices for iio devices in device tree.
> 
> Please use subject prefixes matching the subsystem. You can get them for
> example with `git log --oneline -- DIRECTORY_OR_FILE` on the directory
> your patch is touching.

Sorry, I assumed that was already the case and didn't think of checking
that from what I was given, I'll fix the prefix to "iio: core: .." in v2

> Please run scripts/checkpatch.pl and fix reported warnings. Some
> warnings can be ignored, but the code here looks like it needs a fix.
> Feel free to get in touch if the warning is not clear.

Hm, I did check that and do not get any warning about the code itself:

$ git show --format=email | ./scripts/checkpatch.pl -q
WARNING: DT binding docs and includes should be a separate patch. See: Documentation/devicetree/bindings/submitting-patches.rst

total: 0 errors, 1 warnings, 61 lines checked

What are you thinking of?

Regarding the dt binding, I'm not actually changing a binding so I
didn't think of rechecking after adding the note, but I guess it still
ought to be separate; I'll split it in v2.

> > For platforms without device trees of_alias_get_id will just fail and
> > ida_alloc_range will behave as ida_alloc currently does.
> > 
> > For platforms with device trees, they can not set an alias, for example
> > this would try to get 10 from the ida for the device corresponding to
> > adc2:
> > aliases {
> >   iio10 = &adc2
> > };
> 
> Sorry, that's why you have labels and compatibles.

I'm not sure I understand this comment -- would you rather this doesn't
use aliases but instead add a new label (e.g. `iio,index = <10>` or
whatever) to the iio node itself?

Setting up a fixed alias seems to be precisely what aliases are about
(e.g. setting rtc0 will make a specific node become /dev/rtc0, same with
ethernet0, gpio, i2c, mmc, serial...), I'm not sure I agree a new label
would be more appropriate here, but perhaps I'm missing some context?


Thanks,
-- 
Dominique