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

[Pierre-Louis Bossart]

On 12/17/18 11:39 AM, Mark Brown wrote:
> On Mon, Dec 17, 2018 at 09:03:33AM -0600, Pierre-Louis Bossart wrote:
>
>> 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
> That looks a lot like the CODEC should be exporting a GPIO driver so the
> machine driver doesn't actually need the regmap?  The only register
> touched is _GPIO_CONTROL_1.

I am not sure what you meant by 'exporting a GPIO driver' (mostly 
because I am not familiar with any GPIO framework) but indeed the local 
oscillator choice is controlled by a single register accessible through 
regmap - and changes to that register should only happen when the device 
is a specific state to prevent click/pops.

The machine driver should use clk_set_rate() and not directly handle 
regmap or codec stuff. If it does, or if the clock framework isn't 
relevant here then we can simplify all this as suggested in 
https://patchwork.kernel.org/patch/10444387/. What I was trying to do 
with the github update is to keep the clock framework, tie it closer 
with the codec parts with a state variable that prevents wild changes 
without going back to a 'safe' idle state (similar idea as PulseAudio 
clock changes, which can only happen when the PCM is not opened and used).