[alsa-devel] MPC5200/WM9712 mute problem

[Mark Brown]

On Wed, Aug 05, 2009 at 09:30:53AM -0700, John Bonesio wrote:

> I've retitled the email to better reflect the real patch. I believe
> there has been some general confusion because I originally sent the
> wrong patch.

Retitling again; I don't think we've diagnosed what is causing issues
here.  Doing a quick test here I wasn't able to reproduce this behaviour
so I suspect either the AC97 controller by itself or some interaction
between it and the WM9712.  Like I say, the WM9712 is not a new part and
the drivers aren't new either so it'd be surprising to find an issue
like this now.

> > Like I said before, exactly which control are you adjusting here?

> My description of this got lost in all the confusion. Let me try again.
> We are adjusting the mixer bits for mute/unmute on two of the mixer
> settings. The first one is general headphone mute setting on register
> 0x4 (bit 15). The second one is the PCM mute setting on register 0x18
> (bit 15).

Hrm, so the same bit in both registers.  Suspicious...

> What we are seeing is that if we first unmute the general headphone (reg
> 0x4 bit15), then unmute the PCM (reg 0x18 bit 15) [HPL PCM in the
> alsamixer application], the general headphone gets muted again, even
> though software didn't write to that register.

Are any other bits in register 4 affected or is it only bit 15?

> > My money would be on the AC97 controller having problems; the quality of
> > SoC AC97 controllers is variable.  It certainly doesn't sound like a
> > WM9712 issue; as I say I'd be very surprised if such an issue hadn't
> > come up before given how widely deployed the part is.

> We don't have access to an AC97 analyzer. Do you have any suggestions on
> other ways we can pinpoint the error?

Any scope that can capture would be useful to see what's going on;
obviously decode would have to be by hand.  Coding out the register
cache may also be useful - it'd allow you to see the current hardware
register values.