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

[Lee Jones <lee@kernel.org>]

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.

-- 
Lee Jones [李琼斯]