Re: [RFC 2/2] ASoC: rt5670: Add LED trigger support

[Takashi Iwai <tiwai@suse.de>]

On Wed, 24 Feb 2021 13:08:55 +0100,
Jaroslav Kysela wrote:
> 
> Dne 24. 02. 21 v 12:43 Takashi Iwai napsal(a):
> 
> >>> So far, a user control is merely storing the value, let read/write via
> >>> the control API.  That's all, and nothing wrong can happen just by
> >>> that.  Now if it interacts with other subsystem...
> >>>
> >>> A more serious concern is rather the fragility of the setup; for
> >>> enabling the mute LED control, you'd have to create a new user-space
> >>> control, the function of the control has to be ignored by some
> >>> application and some not, etc.  This has to be done on each machine
> >>
> >> You're using "ignore", but as I explained before, the user space switch will
> >> be used in the whole chain:
> >>
> >> capture stream ->
> >>   alsa-lib mute switch / silence PCM stream ->
> >>   PA mute switch / silence PCM stream
> >>
> >> So PA can use this switch like the traditional hardware mute switch.
> > 
> > Does it mean PA would work as of now without any change?  Or does it
> > need patching?
> 
> Yes, no PA modifications are required with my mechanism. The PA will just see
> the new user space control - mute switch - created in alsa-lib - which will be
> synced the internal PA path mute state like for the hardware mute
> switch.

OK, but how would we create and manage the user control element?  And
why it has to be user control?


thanks,

Takashi