On Thu, 25 Feb 2021 13:14:37 +0100, Anton Yakovlev wrote: > > On 25.02.2021 11:55, Takashi Iwai wrote: > > On Mon, 22 Feb 2021 16:34:41 +0100, > > Anton Yakovlev wrote: > >> +static int virtsnd_pcm_open(struct snd_pcm_substream *substream) > >> +{ > >> + struct virtio_pcm *vpcm = snd_pcm_substream_chip(substream); > >> + struct virtio_pcm_substream *vss = NULL; > >> + > >> + if (vpcm) { > >> + switch (substream->stream) { > >> + case SNDRV_PCM_STREAM_PLAYBACK: > >> + case SNDRV_PCM_STREAM_CAPTURE: { > > > > The switch() here looks superfluous. The substream->stream must be a > > good value in the callback. If any, you can put WARN_ON() there, but > > I don't think it worth. > > At least it doesn't do any harm. It does -- it makes the readability worse, and that's a very important point. > >> +static int virtsnd_pcm_hw_params(struct snd_pcm_substream *substream, > >> + struct snd_pcm_hw_params *hw_params) > >> +{ > > .... > >> + return virtsnd_pcm_msg_alloc(vss, periods, period_bytes); > > > > We have the allocation, but... > > > >> +static int virtsnd_pcm_hw_free(struct snd_pcm_substream *substream) > >> +{ > >> + return 0; > > > > ... no release at hw_free()? > > I know that the free is present in the allocator, but it's only for > > re-allocation case, I suppose. > > When the substream stops, sync_ptr waits until the device has completed > all pending messages. This wait can be interrupted either by a signal or > due to a timeout. In this case, the device can still access messages > even after calling hw_free(). It can also issue an interrupt, and the > interrupt handler will also try to access message structures. Therefore, > freeing of already allocated messages occurs either in hw_params() or in > dev->release(), since there it is 100% safe. OK, then it's worth to document it about this object lifecycle. The buffer management of this driver is fairly unique, so otherwise it confuses readers. thanks, Takashi