On Thu, 22 Feb 2024 18:36:49 +0100,
Jaroslav Kysela wrote:
>
> Return used most significant bits from sample bit-width rather than the whole
> physical sample word size. The starting bit offset is defined in the format
> itself.
>
> The behaviour is not changed for 32-bit formats like S32_LE. But with this
> change - msbits value 24 instead 32 is returned for 24-bit formats like S24_LE
> etc.
>
> Also, commit 2112aa034907 ("ALSA: pcm: Introduce MSBITS subformat interface")
> compares sample bit-width not physical sample bit-width to reset MSBITS_MAX bit
> from the subformat bitmask.
>
> Probably no applications are using msbits value for other than S32_LE/U32_LE
> formats, because no drivers are reducing msbits value for other formats (with
> the msb offset) at the moment.
>
> For sanity, increase PCM protocol version, letting the user space to detect
> the changed behaviour.
>
> Signed-off-by: Jaroslav Kysela <perex@xxxxxxxx>
Hmm, the idea is nice, but I hesitate to take this as is.
Basically the kernel should keep the backward compatibility, and this
won't (although the feature is very minor).
IMO, it'd be safer to check user_pversion and applies the new behavior
only with it being >= 2.0.17, for example.
thanks,
Takashi
> ---
> include/uapi/sound/asound.h | 4 ++--
> sound/core/pcm_native.c | 5 +++++
> 2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index d5b9cfbd9cea..628d46a0da92 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -142,7 +142,7 @@ struct snd_hwdep_dsp_image {
> * *
> *****************************************************************************/
>
> -#define SNDRV_PCM_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 16)
> +#define SNDRV_PCM_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 17)
>
> typedef unsigned long snd_pcm_uframes_t;
> typedef signed long snd_pcm_sframes_t;
> @@ -416,7 +416,7 @@ struct snd_pcm_hw_params {
> unsigned int rmask; /* W: requested masks */
> unsigned int cmask; /* R: changed masks */
> unsigned int info; /* R: Info flags for returned setup */
> - unsigned int msbits; /* R: used most significant bits */
> + unsigned int msbits; /* R: used most significant bits (in sample bit-width) */
> unsigned int rate_num; /* R: rate numerator */
> unsigned int rate_den; /* R: rate denominator */
> snd_pcm_uframes_t fifo_size; /* R: chip FIFO size in frames */
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index f5ff00f99788..21baf6bf7e25 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -486,6 +486,11 @@ static int fixup_unreferenced_params(struct snd_pcm_substream *substream,
> i = hw_param_interval_c(params, SNDRV_PCM_HW_PARAM_SAMPLE_BITS);
> if (snd_interval_single(i))
> params->msbits = snd_interval_value(i);
> + m = hw_param_mask_c(params, SNDRV_PCM_HW_PARAM_FORMAT);
> + if (snd_mask_single(m)) {
> + snd_pcm_format_t format = (__force snd_pcm_format_t)snd_mask_min(m);
> + params->msbits = snd_pcm_format_width(format);
> + }
> }
>
> if (params->msbits) {
> --
> 2.43.0
>
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