[alsa-devel] [PATCH] ALSA - hda: hdmi flag to stop playback when monitor is disconnected

[Yang, Libin]

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Wednesday, November 11, 2015 10:42 PM
> To: Yang, Libin
> Cc: libin.yang at linux.intel.com; David Henningsson; alsa-devel at alsa-
> project.org; mengdong.lin at linux.intel.com
> Subject: Re: [PATCH] ALSA - hda: hdmi flag to stop playback when
> monitor is disconnected
> 
> On Wed, 11 Nov 2015 15:23:42 +0100,
> Yang, Libin wrote:
> >
> >
> > > -----Original Message-----
> > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > Sent: Wednesday, November 11, 2015 10:13 PM
> > > To: libin.yang at linux.intel.com
> > > Cc: David Henningsson; alsa-devel at alsa-project.org;
> > > mengdong.lin at linux.intel.com; Yang, Libin
> > > Subject: Re: [PATCH] ALSA - hda: hdmi flag to stop playback when
> > > monitor is disconnected
> > >
> > > On Wed, 11 Nov 2015 10:02:14 +0100,
> > > Takashi Iwai wrote:
> > > >
> > > > On Wed, 11 Nov 2015 09:39:09 +0100,
> > > > libin.yang at linux.intel.com wrote:
> > > > >
> > > > > From: Libin Yang <libin.yang at linux.intel.com>
> > > > >
> > > > > Add a flag that user can decide to stop HDMI/DP playback when
> > > > > the corresponding monitor is disconnected and refuse to open
> PCM
> > > > > if there is no monitor connected.
> > > > >
> > > > > Background:
> > > > > When a monitor is disconnected and a new monitor is connected,
> > > > > the parameters of the 2 monitors may be different. Audio driver
> > > > > need handle this situation.
> > > > >
> > > > > Besides, stopping playback when monitor is disconnected will
> > > > > help to save the power.
> > > > >
> > > > > Signed-off-by: Libin Yang <libin.yang at linux.intel.com>
> > > >
> > > > Thanks.  Below are just nitpicking, so let's test this patch at first,
> > > > especially to see whether it has any significant influence on PA, then
> > > > respin with the fixes.
> > > >
> > > > David, care to check in your side, too?
> > >
> > > So I tested this with PA 7.1, and it failed, unfortunately.
> > > In short:
> > > - PA needs the PCM access at probe.  If it gets an error, the device
> > >   will be never enumerated again
> >
> > Thanks for test.
> >
> > If so, should we re-write the hdmi_pcm_open() and
> > generic_hdmi_playback_pcm_prepare() function to make
> > the probe works? Or not support dynamic pcm assignment?
> >
> > > - PA removes the device when it's disconnected.  The PCM stop with
> > >   DISCONNECT state leads to the device disappearance.
> >
> > If we can't use DISCONNECT, what else can we use? Or we can't
> > stop PCM when monitor is disconnected?
> 
> One obvious options is: we don't care about it.  Maybe care it only
> when really needed, e.g. return an error only in prepare and cleanup,
> but not in open.

Get it. I will refine the patch.

So we will not care the disconnect when playback and
not stop the PCM?

If we don't stop pcm, how to handle connect a different monitor?
It seems userspace must handle such scenario.

Regards,
Libin

> 
> 
> Takashi