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

[Takashi Iwai]

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.


Takashi