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SubjectRe: [PATCH] SoC: simple-card-utils: set 0Hz to sysclk when shutdown
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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@katsuster.net>
>> ---
>
> 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

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