linux-kernel - Re: [PATCH 1/2] dt-bindings: leds: add generic LED consumer documentation

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Message-ID: <9c536e24-ab5a-454a-93af-6d4c51d4e1ce@kernel.org>
Date: Thu, 4 Sep 2025 12:47:56 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Hans de Goede <hansg@...nel.org>,
 Aleksandrs Vinarskis <alex@...arskis.com>
Cc: robh@...nel.org, bryan.odonoghue@...aro.org, conor+dt@...nel.org,
 devicetree@...r.kernel.org, krzk+dt@...nel.org, lee@...nel.org,
 linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org, pavel@...nel.org
Subject: Re: [PATCH 1/2] dt-bindings: leds: add generic LED consumer
 documentation

On 04/09/2025 12:29, Hans de Goede wrote:
> Hi Krzysztof,
> 
> On 4-Sep-25 11:45 AM, Krzysztof Kozlowski wrote:
>> On 04/09/2025 09:26, Hans de Goede wrote:
>>>>>>> +maintainers:
>>>>>>> +  - Aleksandrs Vinarskis <alex@...arskis.com>
>>>>>>> +
>>>>>>> +description:
>>>>>>> +  Some LED defined in DT are required by other DT consumers, for example
>>>>>>> +  v4l2 subnode may require privacy or flash LED.
>>>>>>> +
>>>>>>> +  Document LED properties that its consumers may define.
>>>>>>
>>>>>> We already have the trigger-source binding for "attaching" LEDs to 
>>>>>> devices. Why does that not work here?
>>>>>
>>>>> I have not actually considered this, as the existing privacy-led solution
>>>>> from the original series is not trigger based. At least one of the reasons
>>>>> for that is that trigger source can be rather easily altered from user
>>>>> space, which would've been bad for this use case. If v4l2 acquires control
>>>>> over the LED it actually removes triggers and disables sysfs on that LED.
>>>>
>>>> So does that mean that v4l2 solves the problem of "trigger source can be
>>>> rather easily altered from user space"?
>>>
>>> Yes, currently the v4l2-core already does:
>>
>> Thanks, I understand that it solves the problem described in the patch,
>> so the patch can be dropped.
> 
> I'm a bit confused now, do you mean that this dt-bindings patch can
> be dropped ?

Yes.

Alex's explanation to Rob felt confusing, so I asked for clarification.
You clarfiied that that v4l2 solves the problem, therefore there is no
problem to be solved.

If there is no problem to be solved, this patch is not needed.

If this patch is needed, just describe the problem accurately.

> 
> The existing v4l2-core code solves getting the privacy-LED on ACPI/x86_64,
> on DT there is no official bindings-docs for directly getting a LED with

There are and Rob pointed to them. If Rob's answer is not enough, make
it explicit.

Really, there are here some long explanations which do not really
explain this in simple terms. Simple term is: "existing property foo
does not work because <here goes the reason>".

Best regards,
Krzysztof