[alsa-devel] [PATCH] ASoC: soc-pcm: Use format size instead physical for sample_bits symmetry

[Peter Ujfalusi]

On 25/07/2019 13.22, Peter Ujfalusi wrote:
> For DAIs the format size in bits matters when it comes to symmetry.
> The physical width is the in-memory format size which matters mostly for
> the platform drivers.
> 
> If for example a DAI requests symmetric_samplebits and the first stream is
> using S24_LE then the second stream would not be allowed to use S24_3LE
> despite both S24_LE and S24_3LE would need the same clocking on the bus.
> But S32_LE would be allowed (S24_LE and S32_LE is both physically 32 bits
> in memory) which would not be compatible with S24_LE on the bus.

Well, this is not correct either as the
snd_pcm_hw_constraint_single(substream->runtime,
			     SNDRV_PCM_HW_PARAM_SAMPLE_BITS,
			     soc_dai->sample_bits);

applies to physical width.

After S24_LE stream with this patch only S24_3LE is allowed opposed to
S24_LE/S32_LE without it.

I don't see how this can be done correctly.

S24_LE should impose constraint S24_LE | S24_3LE and not allow S32_LE.
In theory any format with less than 24bits could be allowed with
slot_width = 24, but this might go too far.

- Péter

> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi at ti.com>
> ---
>  sound/soc/soc-pcm.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
> index 1406f935af22..c70722dc1f4f 100644
> --- a/sound/soc/soc-pcm.c
> +++ b/sound/soc/soc-pcm.c
> @@ -243,7 +243,7 @@ static int soc_pcm_params_symmetry(struct snd_pcm_substream *substream,
>  
>  	rate = params_rate(params);
>  	channels = params_channels(params);
> -	sample_bits = snd_pcm_format_physical_width(params_format(params));
> +	sample_bits = snd_pcm_format_width(params_format(params));
>  
>  	/* reject unmatched parameters when applying symmetry */
>  	symmetry = cpu_dai->driver->symmetric_rates ||
> @@ -932,7 +932,7 @@ static int soc_pcm_hw_params(struct snd_pcm_substream *substream,
>  
>  		codec_dai->rate = params_rate(&codec_params);
>  		codec_dai->channels = params_channels(&codec_params);
> -		codec_dai->sample_bits = snd_pcm_format_physical_width(
> +		codec_dai->sample_bits = snd_pcm_format_width(
>  						params_format(&codec_params));
>  
>  		snd_soc_dapm_update_dai(substream, &codec_params, codec_dai);
> @@ -945,8 +945,7 @@ static int soc_pcm_hw_params(struct snd_pcm_substream *substream,
>  	/* store the parameters for each DAIs */
>  	cpu_dai->rate = params_rate(params);
>  	cpu_dai->channels = params_channels(params);
> -	cpu_dai->sample_bits =
> -		snd_pcm_format_physical_width(params_format(params));
> +	cpu_dai->sample_bits = snd_pcm_format_width(params_format(params));
>  
>  	snd_soc_dapm_update_dai(substream, params, cpu_dai);
>  
> 

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