linux-kernel - Re: [PATCH] ASoC: wm8962: Wait for updated value of WM8962

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Message-ID: <20221107101010.GD10437@ediswmail.ad.cirrus.com>
Date:   Mon, 7 Nov 2022 10:10:10 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Chancel Liu <chancel.liu@....com>
CC:     <lgirdwood@...il.com>, <broonie@...nel.org>, <perex@...ex.cz>,
        <tiwai@...e.com>, <luca.ceresoli@...tlin.com>, <ojeda@...nel.org>,
        <cmo@...exis.com>, <u.kleine-koenig@...gutronix.de>,
        <xiaolei.wang@...driver.com>, <steve@....org>,
        <chi.minghao@....com.cn>, <patches@...nsource.cirrus.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <shengjiu.wang@....com>
Subject: Re: [PATCH] ASoC: wm8962: Wait for updated value of WM8962_CLOCKING1
 register

On Mon, Nov 07, 2022 at 02:38:18PM +0800, Chancel Liu wrote:
> DSPCLK_DIV field in WM8962_CLOCKING1 register is used to generate
> correct frequency of LRCLK and BCLK. Sometimes the read-only value
> can't be updated timely after enabling SYSCLK. This results in wrong
> calculation values. Delay is introduced here to wait for newest value
> from register. The time of the delay should be at least 500~1000us
> according to test.
> 
> Signed-off-by: Chancel Liu <chancel.liu@....com>
> ---
>  sound/soc/codecs/wm8962.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/sound/soc/codecs/wm8962.c b/sound/soc/codecs/wm8962.c
> index b4b4355c6728..563843565f68 100644
> --- a/sound/soc/codecs/wm8962.c
> +++ b/sound/soc/codecs/wm8962.c
> @@ -2503,6 +2503,14 @@ static void wm8962_configure_bclk(struct snd_soc_component *component)
>  		snd_soc_component_update_bits(component, WM8962_CLOCKING2,
>  				WM8962_SYSCLK_ENA_MASK, WM8962_SYSCLK_ENA);
>  
> +	/* DSPCLK_DIV field in WM8962_CLOCKING1 register is used to generate
> +	 * correct frequency of LRCLK and BCLK. Sometimes the read-only value
> +	 * can't be updated timely after enabling SYSCLK. This results in wrong
> +	 * calculation values. Delay is introduced here to wait for newest
> +	 * value from register. The time of the delay should be at least
> +	 * 500~1000us according to test.
> +	 */
> +	msleep(1);

This looks reasonable but for a 1ms delay we should really be
using usleep_range rather than msleep.

Thanks,
Charles