linux-kernel - Re: [PATCH 4/4] dts: iot2050: Support IOT2050-SM variant

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Message-ID: <62be89bb-1ae1-4bf6-9f9e-b6eb68e6504d@siemens.com>
Date: Tue, 19 Dec 2023 16:37:42 +0100
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Tero Kristo <kristo@...nel.org>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Bao Cheng Su <baocheng.su@...mens.com>,
 Chao Zeng <chao.zeng@...mens.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, Li Hua Qian <huaqian.li@...mens.com>
Subject: Re: [PATCH 4/4] dts: iot2050: Support IOT2050-SM variant

On 19.12.23 10:58, Krzysztof Kozlowski wrote:
> On 19/12/2023 10:54, Jan Kiszka wrote:
>>>>> You mean label. Why node names became the ABI? Which interface exposes them?
>>>>
>>>> root@...2050-debian:~# ls -l /sys/class/leds/
>>>> total 0
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 mmc0:: -> ../../devices/platform/bus@...000/4fa0000.mmc/leds/mmc0::
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 mmc1:: -> ../../devices/platform/bus@...000/4f80000.mmc/leds/mmc1::
>>>> lrwxrwxrwx 1 root root 0 Dec 14 21:12 status-led-green -> ../../devices/platform/leds/leds/status-led-green
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 status-led-red -> ../../devices/platform/leds/leds/status-led-red
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 user-led1-green -> ../../devices/platform/leds/leds/user-led1-green
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 user-led1-red -> ../../devices/platform/leds/leds/user-led1-red
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 user-led2-green -> ../../devices/platform/leds/leds/user-led2-green
>>>> lrwxrwxrwx 1 root root 0 Dec 19 08:55 user-led2-red -> ../../devices/platform/leds/leds/user-led2-red
>>>
>>> I replied too fast previous and did not include answer here:
>>>
>>> You have label for that... Somehow all these nodes are half-baked,
>>> without all the expected properties and now you call node name as ABI.
>>> The node name is not the ABI.
>>
>> Well, existing userspace uses those names, and adding the properties
>> would break that interface. Now, does Linux do that?
> 
> I don't think you understood the concept. There is no change for
> userspace. Same interface, same names. No ABI break.

I do understand the impact very well:
open("/sys/class/leds/user-led1-red") has to work for all the variants,
consistently and backward-compatible for userspace.

> 
> Anyway, changing them is not part of this patchset since these are not
> new nodes.

Fine, then we can leave the LED topic aside for now.

I will look into the other comments.

Jan

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