[pulseaudio-discuss] [PATCH 1/3] alsa: fix infinite loop with Intel HDMI LPE

[Tanu Kaskinen]

On Tue, 2019-03-26 at 13:17 +0800, Hui Wang wrote:
> On 2017/12/28 下午6:09, Tanu Kaskinen wrote:
> > The Intel HDMI LPE driver works in a peculiar way when the HDMI cable is
> > not plugged in: any written audio is immediately discarded and underrun
> > is reported. That resulted in an infinite loop, because PulseAudio tried
> > to keep the buffer filled, which was futile since the written audio was
> > immediately consumed/discarded.
> > 
> > This patch adds special handling for the LPE driver: if the active port
> > of the sink is unavailable, the sink suspends itself. A new suspend
> > cause is added: PA_SUSPEND_UNAVAILABLE.
> > 
> > BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=100488
> > ---
> >  src/modules/alsa/alsa-mixer.h       |  1 +
> >  src/modules/alsa/alsa-sink.c        | 22 ++++++++++++++++++++++
> >  src/modules/alsa/module-alsa-card.c | 34 ++++++++++++++++++++++++++++++++++
> >  src/pulsecore/core.h                |  1 +
> >  4 files changed, 58 insertions(+)
> > 
> > diff --git a/src/modules/alsa/alsa-mixer.h b/src/modules/alsa/alsa-mixer.h
> > index 4ebf1922b..3577f435f 100644
> > --- a/src/modules/alsa/alsa-mixer.h
> > +++ b/src/modules/alsa/alsa-mixer.h
> > @@ -364,6 +364,7 @@ int pa_alsa_set_mixer_rtpoll(struct pa_alsa_mixer_pdata *pd, snd_mixer_t *mixer,
> >  struct pa_alsa_port_data {
> >      pa_alsa_path *path;
> >      pa_alsa_setting *setting;
> > +    bool suspend_when_unavailable;
> >  };
> >  
> >  void pa_alsa_add_ports(void *sink_or_source_new_data, pa_alsa_path_set *ps, pa_card *card);
> > diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
> > index 7936cfaca..a80caab2e 100644
> > --- a/src/modules/alsa/alsa-sink.c
> > +++ b/src/modules/alsa/alsa-sink.c
> > @@ -1527,6 +1527,11 @@ static int sink_set_port_cb(pa_sink *s, pa_device_port *p) {
> >              s->set_volume(s);
> >      }
> >  
> > +    if (data->suspend_when_unavailable && p->available == PA_AVAILABLE_NO)
> > +        pa_sink_suspend(s, true, PA_SUSPEND_UNAVAILABLE);
> > +    else
> 
> Hi Tanu,
> 
> We tried to backport this patch to pulseaudio-8.0 (for ubuntu linux
> 16.04),  but after applying this patch, all audio jacks (like headphone,
> line-in/line-out) can't work anymore. If we change the above line as
> below, the problem will disappear.
> 
> else (data->suspend_when_unavailable)
> 
> In theory, if a port is not set suspend_when_unavailable, the port
> should not be changed by this patch. I don't know if it is correct or
> not,  could you please take a look at it?

I don't think your change is correct. This code is run when the sink
changes its port, so there are two ports involved: the old port and the
new one. If the old port caused the sink to be suspended with the
UNAVAILABLE cause, and the new port doesn't require suspending when
it's unavailable, then with your change the sink doesn't get
unsuspended when it should.

In practice your change should be harmless, though, because all ports
on a Intel HDMI LPE card will have the suspend_when_unavailable flag
set, and on other cards the flag is never set.

You didn't specify what the exact problem with headphones etc. is. Is
there an assertion error? I would guess that you're running into this
bug that was introduced by the HDMI LPE fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=104761

Fixing that bug involved rewriting much of the device suspending and
state changing code. I don't know if you want to backport those patches
if your small change seems to make things work well enough, but here's
a list of relevant commits (oldest first, I'm not 100% that this is a
complete list):

3da0de5418b29c90974d0d3e2198c471c39d229f
6ed37aeef28708f8da34a16c7035fa1331fa13cb
d6e39b5e891c767dd42c369d9f118560b8bb24ae
7f201b1fd419b91a226d23ee1e216661ae082dcf
2dff0d6a6a4df2aab6f36212b705489d5af42835
7f09164ed7979210adcdb7674b9d6217fd44ed66
f6fe411b32c0cf5932fb4f169f5288c76bc6923d
0fad369ceb18a8e275e8f74f10f784e0d7476dfb
73b8a57078b94033edf84de2fc0cfbe344c10dcd
b2537a8f38ad71e4dee57263310235abdf2b95a4
ad0616d4c91de52b7cb69e6222efe96961755482
ad15e6e50e737fb55a87bb7def22332f774abce9

-- 
Tanu

https://www.patreon.com/tanuk
https://liberapay.com/tanuk