[pulseaudio-discuss] [alsa-devel] pulseaudio fails to start with kernel 4.11, caused by new snd_hdmi_lpe_audio module)

[Tanu Kaskinen]

On Fri, 2017-03-24 at 23:01 +0100, Hans de Goede wrote:
> Hi,
> 
> On 03/24/2017 07:18 PM, Tanu Kaskinen wrote:
> > On Thu, 2017-03-23 at 09:57 +0100, Takashi Iwai wrote:
> > > On Thu, 23 Mar 2017 04:16:52 +0100,
> > > Pierre-Louis Bossart wrote:
> > > > 
> > > > On 3/21/17 2:56 AM, Hans de Goede wrote:
> > > > > I: [pulseaudio] alsa-sink.c: Using 1.0 fragments of size 352832 bytes
> > > > > (2000.18ms), buffer size is 352832 bytes (2000.18ms)
> > > > > I: [pulseaudio] alsa-sink.c: Time scheduling watermark is 20.00ms
> > > > > I: [pulseaudio] alsa-sink.c: Driver does not support hardware volume
> > > > > control, falling back to software volume control.
> > > > > I: [pulseaudio] alsa-sink.c: Driver does not support hardware mute
> > > > > control, falling back to software mute control.
> > > > > I: [alsa-sink-HdmiLpeAudio] core-util.c: Successfully enabled SCHED_RR
> > > > > scheduling for thread, with priority 5.
> > > > > I: [alsa-sink-HdmiLpeAudio] alsa-sink.c: Starting playback.
> > > > > I: [alsa-sink-HdmiLpeAudio] (alsa-lib)pcm_hw.c: SNDRV_PCM_IOCTL_HWSYNC
> > > > > failed (-32)
> > > > 
> > > > Humm, single period and hw_sync failed, this could be testing the
> > > > robustness of the single-period code and its mapping on multiple DMA
> > > > descriptors? I haven't looked at the alsa module in eons but can't the
> > > > number of periods be forced to two with module parameters while
> > > > keeping the timer-based schedulng?
> > 
> > I think the code doesn't currently support this.
> > 
> > > It's -EPIPE and this is supposed to be the intentional error code from
> > > HDMI LPE audio driver.  The streaming doesn't work when the gfx is
> > > disconnected or the monitor audio is off.  It accepts the open, but it
> > > returns -EPIPE for further accesses.
> > > 
> > > Maybe -EPIPE is no sensible choice, but the problem is that the driver
> > > can't use the PCM DISCONNECT state because PA interprets it being the
> > > complete disconnection of the card object instead of a temporary
> > > disablement of PCM.
> > 
> > So is this a PulseAudio bug?
> > 
> > I: [alsa-sink-HdmiLpeAudio] alsa-sink.c: Starting playback.
> > I: [alsa-sink-HdmiLpeAudio] (alsa-lib)pcm_hw.c: SNDRV_PCM_IOCTL_HWSYNC failed (-32)
> > 
> > The "Starting playback" message is printed just before the
> > snd_pcm_start() call. PulseAudio doesn't check the return value of
> > snd_pcm_start(), but maybe it should? Does the HWSYNC happen in
> > snd_pcm_start()?
> > 
> > Can this EPIPE thing happen also during playback, not just when
> > starting?
> 
> So is this the likely cause of the RT code killing pa, or do you
> still need me to gather perf output ?

The perf output would be interesting.

It's still unclear to me if the hwsync thing is a bug in alsa, or
something that pulseaudio should deal with. If there's no further input
from the alsa developers, would you be able to test a pulseaudio patch
if I write one? First I'd like to check whether the hwsync error
happens inside snd_pcm_start(), and if so, does the error get reported
in the snd_pcm_start() return value. If snd_pcm_start() returns an
error, pulseaudio should probably react to it, although I'm not sure
how. It would be easy to just remove the sink if there's an error, but
I understood Takashi's comment so that it might be an intermittent
error that depends on the graphics state, and if that's the case,
pulseaudio would have to retry when the graphics state changes, but I
don't know what kind of event could be used to get a notification about
the state change.

-- 
Tanu

https://www.patreon.com/tanuk