Re: [PATCH] SoC: simple-card-utils: set 0Hz to sysclk when shutdown

[Katsuhiro Suzuki]

On 2019/09/09 9:31, Kuninori Morimoto wrote:
> Hi Katsuhiro
>
> > This patch set 0Hz to sysclk when shutdown the card.
> >
> > Some codecs set rate constraints that derives from sysclk. This
> > mechanism works correctly if machine drivers give fixed frequency.
> >
> > But simple-audio and audio-graph card set variable clock rate if
> > 'mclk-fs' property exists. In this case, rate constraints will go
> > bad scenario. For example a codec accepts three limited rates
> > (mclk / 256, mclk / 384, mclk / 512).
> >
> > Bad scenario as follows (mclk-fs = 256):
> >     - Initialize sysclk by correct value (Ex. 12.288MHz)
> >       - Codec set constraints of PCM rate by sysclk
> >         48kHz (1/256), 32kHz (1/384), 24kHz (1/512)
> >     - Play 48kHz sound, it's acceptable
> >     - Sysclk is not changed
> >
> >     - Play 32kHz sound, it's acceptable
> >     - Set sysclk to 8.192MHz (= fs * mclk-fs = 32k * 256)
> >       - Codec set constraints of PCM rate by sysclk
> >         32kHz (1/256), 21.33kHz (1/384), 16kHz (1/512)
> >
> >     - Play 48kHz again, but it's NOT acceptable because constraints
> >       do not allow 48kHz
> >
> > So codecs treat 0Hz sysclk as signal of applying no constraints to
> > avoid this problem.
> >
> > Signed-off-by: Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx>
> > ---
>
> I'm not 100% understand your issue.
> .hw_params (= set mclk/sysclk) is not called in bad case ??
> Or it is called but Codec driver ignores it somehow ??

Ah, sorry for confusing. It's not either. hw_params() of machine
driver has been called even if constraints don't have a requested
PCM rate. But it's not expected.

For example, if constraints are 32k, 21.33k, 16k, hw_params() will
be called with 32k when an user requests to play 48k sounds.


> Thank you for your help !!
> Best regards
> ---
> Kuninori Morimoto

Best Regards,
Katsuhiro Suzuki