linux-kernel - Re: [RFC PATCH] ASoC: wm8960: Use physical width for bclk

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Date:   Wed, 15 Mar 2017 09:19:01 +0000
From:   Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:     Daniel Baluta <daniel.baluta@....com>
CC:     <lgirdwood@...il.com>, <broonie@...nel.org>, <tiwai@...e.com>,
        <patches@...nsource.wolfsonmicro.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <shengjiu.wang@...escale.com>, <mihai.serban@....com>,
        <viorel.suman@....com>
Subject: Re: [RFC PATCH] ASoC: wm8960: Use physical width for bclk

On Tue, Mar 14, 2017 at 06:57:02PM +0200, Daniel Baluta wrote:
> bclk is derived from sysclk with the help of bclk_divs. Anyhow, for
> S20_3LE format there is no bclk_divs that could be used to derive
> an exact bclk.
> 
> We can fix this by using storage size instead the exact
> number of bits of the sample when computing bclk.
> 
> With this approach we can play S20_3LE encoded files at the cost of
> some unused BCLK cycles for S20_3LE and S24_LE.
> 
> Signed-off-by: Daniel Baluta <daniel.baluta@....com>
> ---
>  sound/soc/codecs/wm8960.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/soc/codecs/wm8960.c b/sound/soc/codecs/wm8960.c
> index e1429e3..18ca5fc 100644
> --- a/sound/soc/codecs/wm8960.c
> +++ b/sound/soc/codecs/wm8960.c
> @@ -722,7 +722,8 @@ static int wm8960_hw_params(struct snd_pcm_substream *substream,
>  	bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
>  	int i;
>  
> -	wm8960->bclk = snd_soc_params_to_bclk(params);
> +	wm8960->bclk = params_physical_width(params) *
> +		params_channels(params) * params_rate(params);
>  	if (params_channels(params) == 1)
>  		wm8960->bclk *= 2;

Would quite like to see Mark's thoughts on this. Feels a bit to
me (although I am not certain) like we are solving the problem in
the wrong place, isn't this really setting the desired BCLK and
then in wm8960_configure_clocking we should set the lowest BCLK
we can that is greater than or equal to the desired.

Thanks,
Charles