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

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Message-ID: <691f72aa-6d3e-47a1-9efe-a5f7a61ecb72@kernel.org>
Date: Thu, 4 Sep 2025 12:29:38 +0200
From: Hans de Goede <hansg@...nel.org>
To: Krzysztof Kozlowski <krzk@...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

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 ?

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
led_get() AFAICT and I believe that having a binding is mandatory before
we just start adding leds and led-names properties to DT nodes for sensors ?

Maybe for v2 of this patch-set Aleksanders should also add a patch
actually using the new binding in a dts file to make clear that
the intent is to also start using privacy-LEDs in the same way
on DT systems ?

Regards,

Hans