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

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Date: Wed, 28 Feb 2024 17:11:59 +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 08:42:46AM +0100:
> >> Sorry, that's why you have labels and compatibles.
>
> > 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?
> 
> Maybe I don't get your point, but your email said "sysfs", so why do you
> refer to /dev?

I wrote /dev/rtc0, but it also sets the name in /sys, right?
For example /sys/class/rtc/rtc0

As far as I'm aware iio also creates character devices in /dev with the
same name (/dev/iio/iio:deviceX), but our application doesn't use these
at all and has to? look in /sys directly, so normal udev SYMLINK+=
unfortunately isn't applicable or I wouldn't be bothering with all
this..

> > 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?
> 
> No, the devices already have label property.

Thank you for pointing me at the 'label' property, looking at other
subsystems e.g. leds I see paths in sysfs that use labels as I'd like it
to work for iio (/sys/class/leds/<label> and
/sys/devices/platform/<parent>/leds/<label>)

Unfortunately for iio it looks like labels isn't ignored, but instead
create a file in the sysfs directory of the device, e.g. I now have
/sys/bus/iio/devices/iio:device1/label which contains the label string,
so I'm not sure that can be changed easily as that'd be a change of API
for existing users for labels in iio devices?

(I checked briefly and didn't find any, but there seems to be an awful
lot of code in the iio drivers tree about labels so I'm not really
comfortable changing that without some more background on iio first...
Jonathan perhaps has an opinion on this?)

Thanks,
-- 
Dominique