Messages in this thread | | | Subject | Re: [PATCH v5 6/9] ALSA: virtio: PCM substream operators | From | Anton Yakovlev <> | Date | Thu, 25 Feb 2021 13:14:37 +0100 |
| |
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. If something really went wrong, we can check it right in the open callback, which is called the very first.
>> +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.
> thanks, > > Takashi >
-- Anton Yakovlev Senior Software Engineer
OpenSynergy GmbH Rotherstr. 20, 10245 Berlin
| |