[alsa-devel] [PATCH 2/4] ALSA: hda - Return error when open empty hdmi device

[Wang, Xingchao]

> -----Original Message-----
> From: David Henningsson [mailto:david.henningsson at canonical.com]
> Sent: Monday, June 17, 2013 4:24 PM
> To: Wang Xingchao
> Cc: tiwai at suse.de; daniel.vetter at ffwll.ch; alsa-devel at alsa-project.org;
> intel-gfx at lists.freedesktop.org; Wang, Xingchao
> Subject: Re: [PATCH 2/4] ALSA: hda - Return error when open empty hdmi
> device
> 
> On 06/14/2013 05:20 PM, Wang Xingchao wrote:
> > when user open HDMI device 3/7/8, if it has no physical device
> > connected, return error.
> 
> This patch will cause regressions in two big use cases:
> 
>   1) Older chipsets (at least from non-Intel vendors) might not support correct
> ELD reporting. Thus this will cause HDMI audio to stop working there.

Thanks for pointing this out. It's a good case I missed. :) 
I thought ELD info was monitor specific, and reported on common platforms.
But sometimes user get confused when opening a hdmi device and started to play audio,but
hear nothing, even there's no error message. Is there any way for old chipset which has no
correct ELD reporting but do have audio functionality? App should check before really play audio on the device.
> 
>   2) In PulseAudio's current design, PulseAudio probes the device at startup
> and caches the result. Unfortunately, there is no reprobing at plug/unplug, so if
> the monitor is hotplugged, it will not work unless PulseAudio is restarted
> afterwards.

For haswell ult board only,  DDI port D is not supported, this results in screen flicker when playing on third pin.
But for other haswell boards, the DDI port D is normal. So at first glance my idea is to disable opening device
without physical device connecting.

Thanks
--xingchao

> 
> 
> > The bug is from Haswell platform, All pins choose converter 0 by
> > default in hardware level, maybe only pin 1 had valid monitor
> > connected. if user play audio on pin 0/2, pin 1 can get audio data too.
> >
> > Signed-off-by: Wang Xingchao <xingchao.wang at linux.intel.com>
> > ---
> >   sound/pci/hda/patch_hdmi.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
> > index 8db5eb6..d766f40 100644
> > --- a/sound/pci/hda/patch_hdmi.c
> > +++ b/sound/pci/hda/patch_hdmi.c
> > @@ -1139,6 +1139,9 @@ static int hdmi_pcm_open(struct
> hda_pcm_stream *hinfo,
> >   	per_pin = get_pin(spec, pin_idx);
> >   	eld = &per_pin->sink_eld;
> >
> > +	if (!eld->monitor_present || !eld->eld_valid)
> > +		return -EIO;
> > +
> >   	if (codec->vendor_id == 0x80862807)
> >   		hsw_verify_cvt_D0(spec, codec);
> >
> >
> 
> 
> 
> --
> David Henningsson, Canonical Ltd.
> https://launchpad.net/~diwic