linux-kernel - Re: [PATCH v2 1/3] ASoC: es8316: judge PCM rate at later timing

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Date:   Mon, 2 Sep 2019 13:02:49 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Katsuhiro Suzuki <katsuhiro@...suster.net>
Cc:     David Yang <yangxiaohua@...rest-semi.com>,
        Daniel Drake <drake@...lessm.com>,
        Hans de Goede <hdegoede@...hat.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] ASoC: es8316: judge PCM rate at later timing

On Sun, Sep 01, 2019 at 01:26:48AM +0900, Katsuhiro Suzuki wrote:
> This patch change the judge timing about playing/capturing PCM rate.
> 
> Original code set constraints list of PCM rate limits at set_sysclk.
> This strategy works well if system is using fixed rate clock.
> 
> But some boards and SoC (such as RockPro64 and RockChip I2S) has
> connected SoC MCLK out to ES8316 MCLK in. In this case, SoC side I2S
> will choose suitable frequency of MCLK such as fs * mclk-fs when
> user starts playing or capturing.

The best way to handle this is to try to support both fixed and variable
clock rates, some other drivers do this by setting constraints based on
MCLK only if the MCLK has been set to a non-zero value.  They have the
machine drivers reset the clock rate to 0 when it goes idle so that no
constraints are applied then.  This means that if the machine has a
fixed clock there will be constraints, and that constraints get applied
if one direction has started and fixed the clock, but still allows the
clock to be varied where possible.

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