[alsa-devel] [PATCH] conf: HdmiLpeAudio: remove the "front" pcm definition

[Takashi Iwai]

On Wed, 04 Oct 2017 21:44:00 +0200,
Tanu Kaskinen wrote:
> 
> PulseAudio assumes that the "front" pcm device always refers to an
> analog device, not HDMI. While that assumption is not really valid, the
> reality is that without that assumption PulseAudio can't know whether
> "front" and "hdmi" refer to a different or the same device.
> 
> The HDMI LPE driver doesn't allow audio streaming while the HDMI cable
> is unplugged, so PulseAudio has to know when it's plugged in and when
> it's not. If both "front" and "hdmi" devices exist, PulseAudio will
> notice that HDMI is unplugged, but it doesn't know that "front" refers
> to the same device, and PulseAudio will try to use the "front" device
> with bad consequences. The kernel driver's refusal to stream any audio
> makes PulseAudio enter an infinite loop and then the kernel kills
> PulseAudio, because it consumes too much CPU time in a realtime thread.
> 
> While the looping in PulseAudio could probably be fixed, that wouldn't
> change the fact that PulseAudio thinks that there is an analog device. I
> believe it's best to avoid having the same device as both "front" and
> "hdmi" in alsa-lib.
> 
> I removed also the surround configuration includes. I don't think they
> had any effect anyway, so I wonder why they were there in the first
> place.

These definitions are there for LPCM surround channels.

The biggest problem behind the scene is that we mixed up both logical
and physical configurations.  The "front" or "surround51" belong to
the former, while "hdmi" belongs to the latter.

In the past, there was only SPDIF that has only two stereo channels,
so the logical configuration was fixed with that.  We copied that
config for HDMI/DP, and now we hit the inconsistency more clearly...

I suppose the PA issue gets fixed just by this removal?  If yes, I'm
willing to apply it, including in the next release.


thanks,

Takashi

> 
> BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=100488
> ---
>  src/conf/cards/HdmiLpeAudio.conf | 24 ------------------------
>  1 file changed, 24 deletions(-)
> 
> diff --git a/src/conf/cards/HdmiLpeAudio.conf b/src/conf/cards/HdmiLpeAudio.conf
> index 9fa30da0..a1e493da 100644
> --- a/src/conf/cards/HdmiLpeAudio.conf
> +++ b/src/conf/cards/HdmiLpeAudio.conf
> @@ -2,30 +2,6 @@
>  # Configuration for the Intel HDMI/DP LPE audio
>  #
>  
> -<confdir:pcm/front.conf>
> -
> -HdmiLpeAudio.pcm.front.0 {
> -	@args [ CARD ]
> -	@args.CARD {
> -		type string
> -	}
> -	type softvol
> -	slave.pcm {
> -		type hw
> -		card $CARD
> -	}
> -	control {
> -		name "PCM Playback Volume"
> -		card $CARD
> -	}
> -}
> -
> -<confdir:pcm/surround40.conf>
> -<confdir:pcm/surround21.conf>
> -<confdir:pcm/surround41.conf>
> -<confdir:pcm/surround50.conf>
> -<confdir:pcm/surround51.conf>
> -
>  <confdir:pcm/hdmi.conf>
>  
>  HdmiLpeAudio.pcm.hdmi.0 {
> -- 
> 2.14.2
> 
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