[alsa-devel] [PATCH] ASoC: WM9712 Codec: Workaround an unmute problem (Was: Re: [PATCH] ASoC: MPC5200: Support for buffer wrap around)

[Jon Smirl]

On Wed, Aug 5, 2009 at 12:30 PM, John Bonesio<bones at secretlab.ca> wrote:
> Hi Mark,
>
> 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.
>
> You wrote:
>
>> 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).
>
> 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.
>
>>
>> > If there is code in software doing this, it's very subtle.
>>
>> 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?

Do you have a normal logic analyzer? You can decode the AC97 by hand,
its only a couple of frames.

-- 
Jon Smirl
jonsmirl at gmail.com