Re: [PATCH] ALSA: hda - using POS_FIX_LPIB on Broadwell HDMI Audio

[Takashi Iwai <tiwai@suse.de>]

At Thu, 8 May 2014 09:37:13 +0000,
Lin, Mengdong wrote:
> 
> Hi Takashi,
> 
> Is it possible to accept this patch as a quick fix?

Well, the question is whether this is specific to this board, or it's
a generic issue of BDW HDMI controller.  In the latter case, the fix
is done in a wrong place.

> It seems that a driver regression triggers this issue, since we don't have this problem two weeks ago.
> We're still trying to locate the regression and checking the root cause. 

If it's a recent regression, I don't think it's good to apply a
bandaid.  There must be a cause (e.g. something changed in the
graphics side) to fix properly.

> This patch could avoid audio degradation atm before we have a better solution.

The workaround can be applied easily via module option, and the
machine isn't in the market yet.  So I see no point to hurry too much
for now...


thanks,

Takashi


> Thanks
> Mengdong
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai@suse.de]
> > Sent: Thursday, May 08, 2014 2:40 PM
> > To: Yang, Libin
> > Cc: alsa-devel@alsa-project.org; Lin, Mengdong; Pierre-Louis Bossart
> > Subject: Re: [PATCH] ALSA: hda - using POS_FIX_LPIB on Broadwell HDMI Audio
> > 
> > At Thu, 8 May 2014 06:28:17 +0000,
> > Yang, Libin wrote:
> > >
> > > Hi Takashi,
> > >
> > > > -----Original Message-----
> > > > From: Takashi Iwai [mailto:tiwai@suse.de]
> > > > Sent: Thursday, May 8, 2014 2:20 PM
> > > > To: Yang, Libin
> > > > Cc: alsa-devel@alsa-project.org; Lin, Mengdong; Pierre-Louis Bossart
> > > > Subject: Re: [PATCH] ALSA: hda - using POS_FIX_LPIB on Broadwell
> > > > HDMI Audio
> > > >
> > > > At Thu, 8 May 2014 06:13:31 +0000,
> > > > Yang, Libin wrote:
> > > > >
> > > > > Hi Takashi,
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Takashi Iwai [mailto:tiwai@suse.de]
> > > > > > Sent: Thursday, May 8, 2014 1:51 PM
> > > > > > To: Yang, Libin
> > > > > > Cc: alsa-devel@alsa-project.org; Lin, Mengdong; Pierre-Louis
> > > > > > Bossart
> > > > > > Subject: Re: [PATCH] ALSA: hda - using POS_FIX_LPIB on Broadwell
> > > > > > HDMI Audio
> > > > > >
> > > > > > At Thu, 8 May 2014 05:48:04 +0000, Yang, Libin wrote:
> > > > > > >
> > > > > > > Hi Takashi,
> > > > > > >
> > > > > > > I checked the wallclock counter. The counter is OK. But it
> > > > > > > failed to correct
> > > > > > the position.
> > > > > >
> > > > > > So, how wrong the position buffer is?  Is the problem intermittent?
> > > > > > Please elaborate more.
> > > > >
> > > > > The issue is the position is almost always inaccurate. You will
> > > > > hear there is
> > > > intermittent noise in the sound. And the sound is played faster than
> > > > it should be.
> > > > >
> > > > > The following message is what I got from dmesg:
> > > > >
> > > > > [ 73.278117] snd_hda_intel 0000:00:03.0: IRQ timing workaround is
> > > > activated for card #0. Suggest a bigger bdl_pos_adj.
> > > > > [ 73.528575] snd_hda_intel 0000:00:03.0: Unstable LPIB (26240 >=
> > > > > 24064); disabling LPIB delay counting
> > > > >
> > > > > Do you think the print of wallclk and position information in the
> > > > > function
> > > > azx_position_ok() is useful to you? If yes, I will add debug code to
> > > > print the info.
> > > >
> > > > It'd better to have the raw values of posbuf, lpib and wallclock for
> > > > further analysis, yes.
> > > >
> > > > BTW, did you try non-snoop mode via snoop=0 option?
> > >
> > > I haven't tried non-snoop. Do I use `modprobe snd-hda-intel snoop=0` to use
> > non-snoop mode?
> > 
> > Yes.
> > 
> > Takashi
>