[PATCH] ASoC: max98357a: Add mixer control to mute/unmute speaker

[Ajit Kumar Pandey]

On 12/9/2021 2:10 AM, Mark Brown wrote:
> Actually now I look again the only control interface this driver has is
> GPIOs but it does expose a digital interface with constraints as input
> so doesn't fit within simple-amplifier.  However this is just powering
> off the amplifier to achieve mute rather than a separate mute control so
> it'd probably be better to use a SND_SOC_DAPM_PIN_SWITCH() for the
> Speaker widget to do this, this would also end up addressing Jaroslav's
> thing with the naming as a side effect.  Sorry about the confusion there.

Thanks for suggestion. We tried using SND_SOC_DAPM_PIN_SWITCH() for the 
speaker widget and it invoke dapm_event callback based on switch i.e 
max98357a_sdmode_event() but codec driver isn't enabling/disabling gpios 
in such event callback instead they are doing that in dai_ops trigger 
callback. In our platform single I2S controller instance (cpu-dai) is 
connected to two different endpoints with a single PCM device, hence we 
want to switch or enable/disable output based on Machine driver controls 
only.

Initially we thought to configure gpio within sdmode_event callback but
there was some pop noise issue reported in one platform with that change
hence reverted. Check 
https://patchwork.kernel.org/project/alsa-devel/patch/20200721114232.2812254-1-tzungbi@google.com/#23502085
So we thought of exposing a mixer control to enable/disable amp from UCM
in our platform without breaking existing functionality. Please let us
know any other alternative way if possible.