Re: [PATCH v3] ARM: dts: renesas: r9a06g032-rzn1d400-db: describe Debug LEDs

[Jacek Anaszewski <jacek.anaszewski@gmail.com>]

On 5/14/25 17:28, Lee Jones wrote:
> On Mon, 12 May 2025, Jacek Anaszewski wrote:
> 
>> Hi Geert,
>>
>> On 5/12/25 09:13, Geert Uytterhoeven wrote:
>>> Hi Jacek,
>>>
>>> Thanks for your answer!
>>
>> You're welcome.
>>
>>> On Sat, 10 May 2025 at 14:43, Jacek Anaszewski
>>> <jacek.anaszewski@gmail.com> wrote:
>>>> On 5/8/25 15:49, Lee Jones wrote:
>>>>> On Thu, 08 May 2025, Wolfram Sang wrote:
>>>>>> On Thu, Apr 17, 2025 at 01:39:14PM +0200, Geert Uytterhoeven wrote:
>>>>>>> On Thu, 17 Apr 2025 at 11:33, Wolfram Sang
>>>>>>> <wsa+renesas@sang-engineering.com> wrote:
>>>>>>>> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
>>>>>>>> ---
>>>>>>>>
>>>>>>>> Changes since v2:
>>>>>>>> * using function, color, function-enumerator properties now
>>>>>>>>
>>>>>>>> Honestly, this is better than using node names? With V2, the LEDs were
>>>>>>>> named as in the schematics, now they are called:
>>>>>>>>
>>>>>>>> lrwxrwxrwx    1 root     root             0 May 12 12:10 green:programming-0 -> ../../devices/platform/leds/leds/green:programming-0
>>>>>>>> lrwxrwxrwx    1 root     root             0 May 12 12:10 green:programming-1 -> ../../devices/platform/leds/leds/green:programming-1
>>>>>>>> lrwxrwxrwx    1 root     root             0 May 12 12:10 green:programming-2 -> ../../devices/platform/leds/leds/green:programming-2
>>>>>>>> ...
>>>>>>>>
>>>>>>>> Which gets even more confusing if we might later add LEDs not on this
>>>>>>>> board, but on the expansion board. 'green:programming-8' sits where?
>>>>>>>>
>>>>>>>> I really wonder, but if this is the official way now...
>>>>>>>
>>>>>>> Good point!  So I'm inclined to take v2...
>>>>>>>
>>>>>>> Let's raise this with the LED people. I don't want to fight Pavel when
>>>>>>> v2 hits the CiP tree ;-)
>>>>>>
>>>>>> So, if there is no other opinion here, can we remove function, color,
>>>>>> function-enumerator and just use the node names which match the
>>>>>> schematics? Basically apply V2?
>>>>>
>>>>> I didn't author the semantics nor the rules surrounding them, but I am
>>>>> obliged to enforce them.  Therefore "LED people" say, please stick to
>>>>> convention as stated in the present documentation:
>>>>>
>>>>> https://docs.kernel.org/leds/leds-class.html#led-device-naming
>>>>>
>>>>> Please note that a "debug" (LED_FUNCTION_DEBUG) option already exists if
>>>>> that is more appropriate to your use-case.
>>>>>
>>>>> Let's also bring Jacek into the conversion, since I know that he did a
>>>>> bunch of work around this topic.
>>>>
>>>> The question is if the LED name from the schematics tells anything to
>>>> the user of the equipment?
>>>
>>> As this is a development board and not a finished product, I would
>>> answer yes.
>>
>> OK.
>>
>>>> The idea behind LED naming is to facilitate matching the LED class
>>>> device name as reported by the system with the LED location on the
>>>> equipment.
>>>>
>>>> The LED naming standardization intended to enforce consistent
>>>> LED naming, and not allowing to add multiple interchangeable
>>>> names like wifi/wlan. It also helps to keep LED name sections order in
>>>> accordance with Linux documentation, which before had been often
>>>> abused by allowing to assign anything to the now deprecated 'label'
>>>> DT property.
>>>
>>> I agree this all makes perfect sense for a final product, where the
>>> purpose of each LED is clear, and sometimes indicated by an icon
>>> on the case.
>>> For a development board, some LEDs may have a fixed purpose.
>>> But typically there is also a collection of generic user LEDs, which
>>> do not have a fixed purpose, and are identified by a label on the
>>> schematics.  Imposing an arbitrary numbering scheme on the latter is
>>> confusing for the user (developer).
>>
>> Using DT child node name for LED class device name is only
>> a last resort fallback. However if it is devboard and we want to have
>> a reference to the schematics then I'd say it makes sense to take
>> LED names from DT nodes. What about the colors? Are the LEDs replaceable
>> or soldered?
> 
> Looks like this option does what you want:
> 
> https://github.com/torvalds/linux/blob/master/drivers/leds/led-core.c#L578
> 
> For this to execute you need to provide init_data when calling
> *led_classdev_register*(), omit the; label, function, color_present DT
> properties and also init_data's default_label attribute.  At which point
> the DT node name should be taken as the LED class name.

Yep, I know how it works, I wrote that code after all.
Here, I wanted to clarify whether it wouldn't make sense to stick to
the approach with 'function' and 'color' properties if LEDs are fixed
on the board and the colors are known.

 From [0] I infer that LEDs are green, so we should use 'color' DT
property definitely. And as a 'function' we can assign plain text "pcaN"
if you feel it makes sense for that board.

This way you'll get LED name "pcaN:green", that will be according to the
naming standard.

So the node would look like this, for the pca1 LED:

led-1 {
	function = "pca1";
	color = <LED_COLOR_GREEN>;
	default-state = "keep";
};

[0] 
https://patchwork.kernel.org/project/linux-renesas-soc/patch/20250328153134.2881-11-wsa+renesas@sang-engineering.com/#26336000

-- 
Best regards,
Jacek Anaszewski