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pcm: clarify and fix default sbits (msbits) value for all formats

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As described in the kernel patch (link bellow), the significant (resolution)
bits should be related to the usable sample bits not the physical sample bits.

Link: https://lore.kernel.org/linux-sound/20240222173649.1447549-1-perex@perex.cz/
Link: https://github.com/larsimmisch/pyalsaaudio/pull/146
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
This commit is contained in:
Jaroslav Kysela 2024-02-23 21:50:01 +01:00
parent 431f69a8c3
commit 13057b74c8
3 changed files with 31 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

7
src/pcm/pcm.c
View file

@ -215,7 +215,8 @@ range, thus you may get the significant bits for linear samples via
#snd_pcm_hw_params_get_sbits() function. The example: ICE1712
chips support 32-bit sample processing, but low byte is ignored (playback)
or zero (capture). The function snd_pcm_hw_params_get_sbits()
returns 24 in this case.
returns 24 in this case. The significant bits are related to the usable
sample bits (width) not the physical sample space.
\section alsa_transfers ALSA transfers
@ -3905,6 +3906,10 @@ int snd_pcm_hw_params_get_rate_numden(const snd_pcm_hw_params_t *params,
* \param params Configuration space
* \return signification bits in sample otherwise a negative error code if the info is not available
*
* Significant bits are related to usable sample bits (width) not the
* physical sample bits (width). For non-linear formats, this value may have
* a special meaning which may be defined in future.
*
* This function should only be called when the configuration space
* contains a single configuration. Call #snd_pcm_hw_params to choose
* a single configuration from the configuration space.

22
src/pcm/pcm_hw.c
View file

@ -379,12 +379,28 @@ static int snd_pcm_hw_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
return 0;
}
static inline int hw_params_call(snd_pcm_hw_t *pcm_hw, snd_pcm_hw_params_t *params)
#define hw_param_mask(params,var) \
&((params)->masks[(var) - SND_PCM_HW_PARAM_FIRST_MASK])
static int hw_params_call(snd_pcm_hw_t *pcm_hw, snd_pcm_hw_params_t *params)
{
int err;
/* check for new hw_params structure; it's available from 2.0.2 version of PCM API */
if (SNDRV_PROTOCOL_VERSION(2, 0, 2) <= pcm_hw->version)
return ioctl(pcm_hw->fd, SNDRV_PCM_IOCTL_HW_PARAMS, params);
return use_old_hw_params_ioctl(pcm_hw->fd, SND_PCM_IOCTL_HW_PARAMS_OLD, params);
err = ioctl(pcm_hw->fd, SNDRV_PCM_IOCTL_HW_PARAMS, params);
else
err = use_old_hw_params_ioctl(pcm_hw->fd, SND_PCM_IOCTL_HW_PARAMS_OLD, params);
if (err >= 0 && pcm_hw->version < SNDRV_PROTOCOL_VERSION(2, 0, 17) && params->msbits > 0) {
snd_mask_t *m = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
if (snd_mask_single(m)) {
snd_pcm_format_t format = snd_mask_min(m);
int width = snd_pcm_format_width(format);
if (width > 0 && params->msbits > (unsigned int)width)
params->msbits = width;
}
}
return err;
}
static int snd_pcm_hw_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)

6
src/pcm/pcm_params.c
View file

@ -2075,6 +2075,7 @@ int snd_pcm_hw_refine_soft(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_hw_params_t
{
unsigned int k;
snd_interval_t *i;
snd_mask_t *m;
unsigned int rstamps[RULES];
unsigned int vstamps[SND_PCM_HW_PARAM_LAST_INTERVAL + 1];
unsigned int stamp = 2;
@ -2159,6 +2160,11 @@ int snd_pcm_hw_refine_soft(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_hw_params_t
i = hw_param_interval(params, SND_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 = snd_mask_min(m);
params->msbits = snd_pcm_format_width(format);
}
}
if (!params->rate_den) {