[PATCH] [RFC] ALSA: control - add generic LED API to sound core routines

[Takashi Iwai]

On Sun, 07 Feb 2021 21:11:57 +0100,
Jaroslav Kysela wrote:
> 
> [DO NOT MERGE!]
> [This is just an early proposal for comments]
> [The code is not tested / debugged]
> 
> The recent laptops have usually two LEDs assigned to reflect
> the speaker and microphone mute state. This implementation
> adds a tiny layer on top of the control API which calculates
> the state for those LEDs using the driver callbacks.
> 
> Two new access flags are introduced to describe the controls
> which affects the audio path settings (an easy path for drivers).
> 
> The LED resource can be shared with multiple sound cards with
> this code. The user space controls may be added to the state
> chain, too.
> 
> This code should replace the LED code in the HDA driver and
> add a possibility to easy extend the other drivers (ASoC
> codecs etc.).

Having a common helper in the ALSA core sounds like a good way to go.

My slight concern is that this will end up having the dependency on
LEDS stuff unconditionally when CONFIG_SND_LED=y.

Also, are those new access flags exposed to user-space intentionally,
so that user-space gets some information?

Last but not least: I'm not sure whether we should limit to only two
LEDs (mic and spk).  I'm afraid that there will be more LEDs in
future; people love decorations :)


thanks,

Takashi