Hi, On Sun, May 30, 2021, at 16:32, Takashi Iwai wrote: > On Sat, 29 May 2021 05:33:53 +0200, > Takashi Sakamoto wrote: >> >> Regarding to handling [U|S][32|24] PCM formats, many userspace >> application developers and driver developers have confusion, since they >> require them to understand justification or padding. It easily >> loses consistency and soundness to operate with many type of devices. In >> this commit, I attempt to solve the situation by adding comment about >> relation between [S|U]32 formats and 'msbits' hardware parameter. >> >> The formats are used for 'left-justified' sample format, and the available >> bit count in most significant bit is delivered to userspace in msbits >> hardware parameter (struct snd_pcm_hw_params.msbits), which is decided by >> msbits constraint added by pcm drivers (snd_pcm_hw_constraint_msbits()). >> >> In driver side, the msbits constraint includes two elements; the physical >> width of format and the available width of the format in most significant >> bit. The former is used to match SAMPLE_BITS of format. (For my >> convenience, I ignore wildcard in the usage of the constraint.) >> >> As a result of interaction between ALSA pcm core and ALSA pcm application, >> when the format in which SAMPLE_BITS equals to physical width of the >> msbits constaint, the msbits parameter is set by referring to the >> available width of the constraint. When the msbits parameter is not >> changed in the above process, ALSA pcm core set it alternatively with >> SAMPLE_BIT of chosen format. >> >> In userspace application side, the msbits is only available after calling >> ioctl(2) with SNDRV_PCM_IOCTL_HW_PARAMS request. Even if the hardware >> parameter structure includes somewhat value of SAMPLE_BITS interval >> parameter as width of format, all of the width is not always available >> since msbits can be less than the width. >> >> I note that [S|U24] formats are used for 'right-justified' 24 bit sample >> formats within 32 bit frame. The first byte in most significant bit >> should be invalidated. Although the msbits exposed to userspace should be >> zero as invalid value, actually it is 32 from physical width of format. >> >> Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx> > > Thanks, applied. > > > Takashi I can not find the patch in your tree. Would I ask you to review again? If it should be going to be applied, I'd like you to fix my typo in the subject line; * "[S|U32]" -> "[S|U]32" Regards Takashi Sakamoto
