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

From: Takashi Iwai <tiwai@suse.de>
To: Mark Brown <broonie@kernel.org>
Cc: Oder Chiou <oder_chiou@realtek.com>,
	alsa-devel@alsa-project.org, Liam Girdwood <lgirdwood@gmail.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Bard Liao <bard.liao@intel.com>
Subject: Re: [RFC 2/2] ASoC: rt5670: Add LED trigger support
Date: Tue, 23 Feb 2021 15:21:42 +0100	[thread overview]
Message-ID: <s5h8s7evp8p.wl-tiwai@suse.de> (raw)
In-Reply-To: <20210223140930.GH5116@sirena.org.uk>

On Tue, 23 Feb 2021 15:09:30 +0100,
Mark Brown wrote:
> 
> On Tue, Feb 23, 2021 at 02:59:17PM +0100, Hans de Goede wrote:
> > On 2/23/21 2:45 PM, Mark Brown wrote:
> > > On Mon, Feb 15, 2021 at 03:24:19PM +0100, Hans de Goede wrote:
> 
> > > Why just these particular controls - what if a system has separate mutes
> > > for speakers or something?
> 
> > These are the main volume controls, which are always in the output / input
> > path independent on if we are outputting to e.g. speakers or the headphones.
> 
> > We want to use the main volume control for this, because there always is
> > only 1 output mute LED and 1 input mute LED. Well at least that is the assumption
> > the current ledtrig-audio.c code has.
> 
> > The idea is to only turn the single LED on if we are sure there will be not
> > sound output on any of the outputs, which is why we tie the LED to the
> > mute switch on the main volume control.
> 
> Right, so that might work well on your particular system with your
> particular configuration but will it work well on other systems with
> different hardware?  It's not clear to me that it makes sense to go
> through all the drivers picking controls that might be used for this
> purpose - it seems both time consuming and error prone.  Consider a
> mostly digital device which has an ADC/DAC per input/output rather than
> a central ADC/DAC with analogue muxing for example, or a system with
> multiple DACs available for mixing together or analogue bypassess.  

That's one of my concerns in the recent actions for putting the
hard-coded mute LED controls.  So far, the only usage of led-audio
trigger is HD-audio, and it's enabled only for selected devices and
setups.  OTOH, if we apply the audio-led trigger generically in ASoC
codec driver, it's always done and might misfit; e.g. what happens if
two codecs are present on the system?.

Of course, this implementation would make the integration much easier,
and that's a big benefit.  So I have a mixed feeling and not decided
yet whether we should go for it right now...

thanks,

Takashi