[alsa-devel] Need help fixing pop/click artifacts in an ASOC driver

[Dimitris Papavasiliou]

On 12/17/18 2:37 PM, Mark Brown wrote:
> On Mon, Dec 17, 2018 at 02:17:45PM +0200, Dimitris Papavasiliou wrote:
> 
>> Even worse, it would let the pop through at full volume, as it
>> doesn't depend on the gain.  Still, there doesn't seem to be a
>> safe way to avoid the pop altogether, as far as I can see, since
>> the only way I have found to avoid it, is to suspend the chip
>> during the switch, and I can't synchronize access to the relevant
>> register by the machine and CODEC drivers.
> 
>> If you have any other ideas/pointers on approaches I could
>> investigate, please let me know.
> 
> If you're doing this during DAPM there shouldn't be anything else
> running on the card at the time.

In general the clocks need to be switched during the hw_params
callback (when the new callback specifies a new sample rate,
which needs the other clock) and, as far as I can see, this can
happen at more or less any time, i.e. in all power states and
regardless of whether the device is opened or closed.

I can't therefore depend on DAPM functionality to suspend the
chip when needed, as far as I can see at least and apart from
asking the DAPM to force-suspend the chip, as I've already
suggested.