[alsa-devel] Choosing the sysclk in simple-card looks broken to me.

[Nicolin Chen]

On Sun, Aug 10, 2014 at 10:10:51PM -0400, jonsmirl at gmail.com wrote:
> As I debug further I am getting a better understanding of the problem.
> This is my simple-audio binding.
> 
> sound {
> compatible = "simple-audio-card";
> simple-audio-card,format = "i2s";
> 
> simple-audio-card,cpu {
> sound-dai = <&iis0>;
> };
> 
> simple-audio-card,codec {
> clocks = <&iis0>;
> sound-dai = <&sgtl5000>;
> };
> };
> 
> I'm having trouble with the simple-audio-card,cpu node, not the
> simple-audio-card,codec node.  As simple-audio is currently
> implemented when simple-audio-card,cpu is processed it will pick up my
> 80Mhz apb clock and set it as sysclk.

It looks like the problem is that Simple Card also configures cpu-dai
via set_sysclk() with direction SND_SOC_CLOCK_IN while it fetches the
sysclk rate not from MCLK source but from 'sound-dai' -- cpu-dai node
itself, when the binding for sound-dai doesn't have clock or frequency
assignment, although this fetching works out for codec-dai side.

In your case, Simple Card sets both sides of dai with different sysclk
rates, and meanwhile the sysclk rate for cpu-dai is incorrect.

Is it true?

> After spending all day trying to fix that else clause, I'm coming to
> the conclusion that the else clause simply shouldn't be there at all.
> I just hit this because I had code checking for bogus values in
> setsysclk.

Well, even if there's a problem at this point for Simple Card, I'm
still curious for the reason why setting cpu-dai with an incorrect
rate but direction SND_SOC_CLOCK_IN would result some breaks here.

The sysclk direction is only valid when indicating MCLK as sysclk
(FSYNC or BCLK shall follow CBS_CFS/CBM_CFM setting).So basically
if cpu-dai driver gets sysclk configuration with SND_SOC_CLOCK_IN,
shouldn't it just set the internal direction for MCLK's PAD and
return the call directly? (I'm guessing there also might be some
tiny work for your cpu-dai driver to enhance the validation part.)

Best regards,
Nicolin