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

[Takashi Iwai]

At Mon, 12 May 2014 08:22:13 +0000,
Lin, Mengdong wrote:
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de]
> > Sent: Friday, May 09, 2014 6:20 PM
> > To: Lin, Mengdong
> > Cc: David Henningsson; Yang, Libin; anssi.hannula at iki.fi;
> > alsa-devel at alsa-project.org; Pierre-Louis Bossart
> > Subject: Re: [alsa-devel] [PATCH] ALSA: hda - using POS_FIX_LPIB on Broadwell
> > HDMI Audio
> > 
> > At Fri, 9 May 2014 10:08:19 +0000,
> > Lin, Mengdong wrote:
> > >
> > > Hi,
> > >
> > > We found the Broadwell HDMI audio regression is introduced by this patch:
> > >
> > > commit dcb32ecd9a533f47ab652c5c5680bc50a7a822cd
> > > Author: Anssi Hannula <anssi.hannula at iki.fi>
> > > Date: Tue Apr 8 12:36:42 2014 +0300
> > > ALSA: hda - Do not assign streams in reverse order
> > >
> > > We'll further check the root cause.
> > > Since this patch seems only affect the stream ID. Actually Intel GPU tool only
> > find the stream ID is changed by this patch.
> > >
> > > In addition, Haswell HDMI audio is not affected and works well. It seems
> > there is HW behavior difference between HSW and BDW.
> > 
> > Thanks for spotting out!
> > 
> > This sounds like a weird hardware bug of BDW.  If any, we'd need to introduce
> > a flag indicating flipping this  lookup behavior depending on the chip.
> 
> In the display HD-A controller of HSW/BDW, there are 3 sets of stream descriptors registers which controls the DMA engines to transfer audio data over HD-A link:
> set #0: 0x80 ~ 0x9c SD0CTL ~ SD0BDPU
> set #1: 0xa0 ~ 0xbc SD1CTL ~ SD1BDPU
> set #2: 0xc0 ~ 0xdc SD2CTL ~ SD2BDPU
> 
> Test shows that
> On HSW, DMA update on all 3 sets of registers are okay.
> On BDW, DMA update on set #1 and #2 are okay, but is buggy on set #0. Since the three sets of registers have the same definition according to spec and driver behavior is also same, it seems to be a HW issue.
> 
> Maybe we'll have to use the original reverse lookup order for BDW HDMI/DP audio.

I wonder what if you run three streams.  Is the set#0 always broken,
or broken only when used alone?  In the former case, the fix would to
mask the first slot.  In the latter case, back to reverse assignment
would work around it.


Takashi