[alsa-devel] [PATCH BAT V1 0/7] BAT: Add Basic Audio Tester command line tool

[Caleb Crome]

On Thu, Sep 17, 2015 at 10:42 AM, Mark Brown <broonie at kernel.org> wrote:
> On Thu, Sep 17, 2015 at 06:29:58AM -0700, Caleb Crome wrote:
>
>> > Yes, PM suspend and resume of device. We have some scripts (to be
>> > upstreamed later) that would play audio, suspend the device, resume the
>> > device and then retest the audio.
>
>> That seems particularly likely to result in multiple codecs getting
>> out of phase alignment.  i.e. when restarting, you want to be sure to
>> follow the same startup procedure as the first time to make sure all
>> codecs are aligned.
>
> Why should resume be any different from initial system power up?

Heh, perhaps only because I don't understand how it all works :-)

The example I was thinking of is if the card gets partially powered
down.  For example, start recording on 8 channels (4 codecs, called 0,
1, 2, 3 in this example).  At this point, all's well, and all 4 codecs
are in perfect phase sync.

Then switch to playing 2 channel mode with codec 0 only.  Since codecs
1, 2, 3 are no longer needed, then they could get powered down.

Then, switch back to 8 channel mode -- codec 0 is up and running, and
now you want to turn on codecs 1, 2, 3.  At this point it's literally
impossible to resync them with codec 0 without powering down codec 0
and starting from scratch.  This is true of the TLV320AIC seris of
codecs.  The CS53L30 has a dedicated sync pin on the other hand, so
could perhaps recover gracefully in this situation.

-Caleb