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

[Pierre-Louis Bossart]

On 12/17/18 6:17 AM, Dimitris Papavasiliou wrote:
> On 12/13/18 7:42 PM, Mark Brown wrote:
>> On Sat, Nov 24, 2018 at 10:17:49PM +0200, Dimitris Papavasiliou wrote:
>>
>>> discussion here.  I still feel that fixing the machine driver, so
>>> that it doesn't generate the pop at all would be desirable, as
>>> I'm not sure whether the digital_mute callback is guaranteed to
>>> have muted the device when the clock source takes place.
>>
>> Making the machine driver more robust is definitely better, it's more
>> robust in case the mute is for example just a very low gain which might
>> still let the pop through at a lower level.
>
> 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.
>
I started prototyping a different approach where the codec driver passes 
the regmap information to the clock driver. What's missing in the 
patchset is the addition of a clock control in the machine driver, and 
logic added so that rate  change can only be done in a hw_params if 
there was a complete stop and reset on a DAPM_OFF event. compile-tested 
only for now.

https://github.com/plbossart/sound/commits/hifiberry/clks