Re: [PATCH v2 06/17] leds: leds-nuc: allow changing the LED colors

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Hi Marek,

Em Wed, 19 May 2021 09:57:13 +0200
Marek Behún <kabel@kernel.org> escreveu:

> We have multicolor LED framerwork in Linux. This should be implemented
> via that framework. Please do not implement your own way for RGB leds.
> 
> Marek

I saw the multicolor LED framework, but IMO it won't fit here.

See, Linux doesn't have direct access to the LED. The access is
provided via ACPI WMI.

The way BIOS reports the type of the led is via a bitmap flag.
So, the same LED can be represented with either single-color
or multi-color one. See:
	https://www.intel.com/content/dam/support/us/en/documents/intel-nuc/WMI-Spec-Intel-NUC-NUC10ixFNx.pdf

	Table 2.2 LED Color Type
	Bit Number	Type
	0		Dual-color Blue / Amber
	1		Dual-color Blue / White
	2		RGB-color
	3		Single-color LED

Also as each NUC can support up to 7, and they may have a mix of
single color, dual color and RGB LEDs, if we would use the
multicolor class for the colored ones, that would mean that the
code will need to be duplicated, as, depending on what the BIOS
reports, the LED would need to be exposed either as via
led-multicolor-class or as leds-class. 

Worse than that, there's even a WMI command that would allow
to "switch LED type" (see page 8). On other words, the BIOS can
expose a "virtual" single-color LED, but actually implemented
in hardware using a RGB one, and this can be changed in real time.

(note: I didn't implement support yet for this, as the hardware
I have doesn't seem to support the "switch LED type" command).

Thanks,
Mauro