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

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Date:   09 Sep 2019 12:54:45 +0900
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Katsuhiro Suzuki <katsuhiro@...suster.net>
Cc:     Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] SoC: simple-card-utils: set 0Hz to sysclk when shutdown


Hi Katsuhiro

> >> 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
(snip)
> 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.

Oh, I see.
Thank you for explaining.

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