linux-kernel - Re: [PATCH v2 2/2] ASoC: fsl_asrc: always use internal ratio

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Message-ID: <20200716233742.GA27376@Asurada-Nvidia>
Date:   Thu, 16 Jul 2020 16:37:46 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Arnaud Ferraris <arnaud.ferraris@...labora.com>
Cc:     alsa-devel@...a-project.org, Timur Tabi <timur@...nel.org>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Shengjiu Wang <shengjiu.wang@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [PATCH v2 2/2] ASoC: fsl_asrc: always use internal ratio

On Thu, Jul 16, 2020 at 05:13:54PM +0200, Arnaud Ferraris wrote:
> Even though the current driver calculates the dividers to be used
> depending on the clocks and sample rates, enabling the internal ratio
> can lead to noticeable improvements in the audio quality, based on my
> testing.
> 
> As stated in the documentation, "When USRx=1 and IDRx=0, ASRC internal
> measured ratio will be used", so setting this bit even when not in
> "Ideal Ratio" mode still makes sense.
> 
> Signed-off-by: Arnaud Ferraris <arnaud.ferraris@...labora.com>
> ---
>  sound/soc/fsl/fsl_asrc.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/fsl/fsl_asrc.c b/sound/soc/fsl/fsl_asrc.c
> index 6d43cab6c885..0b79a02d0d76 100644
> --- a/sound/soc/fsl/fsl_asrc.c
> +++ b/sound/soc/fsl/fsl_asrc.c
> @@ -465,7 +465,7 @@ static int fsl_asrc_config_pair(struct fsl_asrc_pair *pair, bool use_ideal_rate)
>  	regmap_update_bits(asrc->regmap, REG_ASRCTR,
>  			   ASRCTR_ATSi_MASK(index), ASRCTR_ATS(index));
>  	regmap_update_bits(asrc->regmap, REG_ASRCTR,
> -			   ASRCTR_USRi_MASK(index), 0);
> +			   ASRCTR_USRi_MASK(index), ASRCTR_USR(index));
>  
>  	/* Set the input and output clock sources */
>  	regmap_update_bits(asrc->regmap, REG_ASRCSR,
> @@ -507,8 +507,7 @@ static int fsl_asrc_config_pair(struct fsl_asrc_pair *pair, bool use_ideal_rate)
>  
>  	/* Enable Ideal Ratio mode */

The code is against the comments now -- need to update this line.

>  	regmap_update_bits(asrc->regmap, REG_ASRCTR,
> -			   ASRCTR_IDRi_MASK(index) | ASRCTR_USRi_MASK(index),
> -			   ASRCTR_IDR(index) | ASRCTR_USR(index));
> +			   ASRCTR_IDRi_MASK(index), ASRCTR_IDR(index);

The driver falls back to ideal ratio mode if there is no matched
clock source. Your change seems to apply internal ratio mode any
way? Probably would break the fallback routine.