Date:	Tue, 01 Jul 2008 17:16:43 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Johannes Weiner <hannes@...urebad.de>
Cc:	Mathieu Chouquet-Stringer <mchouque@...e.fr>,
	Jaroslav Kysela <perex@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: Longstanding bug in ac97/intel8x0 resume/init

At Tue, 01 Jul 2008 17:12:02 +0200,
Johannes Weiner wrote:
> 
> Hi,
> 
> Takashi Iwai <tiwai@...e.de> writes:
> 
> > At Tue, 01 Jul 2008 16:37:42 +0200,
> > Johannes Weiner wrote:
> >> 
> >> Hi,
> >> 
> >> Takashi Iwai <tiwai@...e.de> writes:
> >> 
> >> > At 30 Jun 2008 20:58:03 +0200,
> >> > Mathieu Chouquet-Stringer wrote:
> >> >> 
> >> >>         Hey there,
> >> >> 
> >> >> hannes@...urebad.de (Johannes Weiner) writes:
> >> >> > Johannes Weiner <hannes@...urebad.de> writes:
> >> >> > > my laptop has muted sound after resuming the soundcard (by
> >> >> > > s2ram/hibernation).  The problem seems to be that the cached register
> >> >> > > values are not written back to the device properly.
> >> >> 
> >> >> I've got the same exact issue on a Thinkpad T30:
> >> >> 
> >> >>  0 [I82801CAICH3   ]: ICH - Intel 82801CA-ICH3
> >> >>                       Intel 82801CA-ICH3 with AD1881A at irq 5
> >> >> 
> >> >> 00:1f.5 Multimedia audio controller: Intel Corporation 82801CA/CAM AC'97 Audio Controller (rev 02)
> >> >
> >> > Does this happen for both hibernation and S2RAM?
> >> > And, resetting the mixer repairs the mute state, right?
> >> > If yes, the problem appears independently from the codec chip.  Hmm...
> >> 
> >> Yes, happens in both cases here.
> >> 
> >> The alsamixer shows the state of the channels before the suspension(!).
> >
> > Yes.  The driver returns the cached values.
> 
> Okay.
> 
> >> If I change the channel state, the sound works again.  No complete reset
> >> needed at all, I just have to increase/decrease the value a bit (for
> >> each affected channel).
> >
> > Just touching one mixer element?
> 
> What means `element' here?  I have to touch MASTER and PCM in order to
> get some output again, at least ;)

Well, for example, some laptops with maestro3 have a similar problem,
but in that case, you just need to touch one mixer element
(e.g. Master), and you don't have to re-adjust PCM volume.

> >> >From my experiments with the code, I figured that the cached register
> >> values are not written back properly on resume.  The cache is in the
> >> correct state but the hardware is not.  This also explains the behaviour
> >> when changing the channels with alsamixer; the register cache is touched
> >> and written back (and this time, the value really gets through to the
> >> hardware).
> >
> > Right.  
> >
> > snd_ac97_resume() has a check whether the write to MASTER register
> > succeeds, but its timeout is 100ms.  Could you check whether this
> > check passes at resume or failed?  I remember that some device
> > actually passed the test but didn't update the real hardware state.
> > If it failed on yours, we may simply extend the timeout, or make it
> > pending somehow.  If the hardware fools us, however, it'd be toucher.
> 
> By experimentation I found that the writeback works with a two seconds
> delay before writeback.  I can't remember if it was before or after the
> check.  Another approach was to hammer down the value by writing and
> reading back in a loop until the hardware responded with the correct
> value.
> 
> I will redo the tests later and report back to you what helped.

Yeah, that'll be appreciated.


thanks,

Takashi
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