ASoC: sun8i-codec: Automatically set the system sample rate

ASoC: sun8i-codec: Automatically set the system sample rate

The sun8i codec has three clock/sample rate domains:
 - The AIF1 domain, with a sample rate equal to AIF1 LRCK
 - The AIF2 domain, with a sample rate equal to AIF2 LRCK
 - The SYSCLK domain, containing the ADC, DAC, and effects (AGC/DRC),
   with a sample rate given by a divisor from SYSCLK. The divisor is
   controlled by the AIF1_FS or AIF2_FS field in SYS_SR_CTRL, depending
   on if SYSCLK's source is AIF1CLK or AIF2CLK, respectively. The exact
   sample rate depends on if SYSCLK is running at 22.6 MHz or 24.6 MHz.

When an AIF (currently only AIF1) is active, the ADC and DAC should run
at that sample rate to avoid artifacting. Sample rate conversion is only
available when multiple AIFs are active and are routed to each other;
this means the sample rate conversion hardware usually cannot be used.

Only attach the event hook to the channel 0 AIF widgets, since we only
need one event when a DAI stream starts or stops. Channel 0 is always
brought up with a DAI stream, regardless of the number of channels in
the stream.

The ADC and DAC (along with their effects blocks) can be used even if
no AIFs are in use. In that case, we should select an appropriate sample
rate divisor, instead of keeping the last-used AIF sample rate.
44.1/48 kHz was chosen to balance audio quality and power consumption.

Since the sample rate is tied to active AIF paths, disabling pmdown_time
allows switching to the optimal sample rate immediately, instead of
after a 5 second delay.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20201014061941.4306-11-samuel@sholland.org
Signed-off-by: Mark Brown <broonie@kernel.org>