On Sun, 12 Dec 2021 12:30:30 +0100, Takashi Sakamoto wrote: > > 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? Hrm, it seems that the commit was lost by some reason. Sorry! > 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" There was another similar typo in the patch description and I corrected both. Now applied to for-next, commit fb6723daf89083a0d2290f3a0abc777e40766c84. thanks, Takashi
