20.04.2014 20:44, David Henningsson wrote:
On 2014-04-19 23:21, Alexander E. Patrakov wrote:
Since the dca ALSA plugin is based on extplug, it has a slave and
therefore
a card. Thus, PulseAudio thinks that it looks like hardware and attempts
rewinds, which this plugin cannot handle correctly, because ALSA never
notifies extplug plugins about rewinds.
The same mishandling of rewinds applies to some other plugins.
This sounds like an alsa-lib bug, and thus it would be wiser to correct
it in ALSA rather than in PulseAudio?
Yes, this is a bug in alsa-lib. As for the "would it be wiser" question,
I don't have an answer yet. I will try and see what happens. My main
worry is that it will surely make all plugs non-rewindable, and thus has
a very high potential of unfixable regressions for applications that do
rewinds in the legacy non-pulseaudio setup.
Work around this ALSA bug by switching to IRQ-based scheduling on strange
plugin types.
---
I have not deleted the "does a card exist" check, but for the AC3 encoder
case (which is mentioned in the git log) it is now redundant. Feel free
to delete if no other triggering use case is known.
P.S. I see this line in alsa-lib/src/pcm/pcm_extplug.c:
params->info &= ~(SND_PCM_INFO_MMAP | SND_PCM_INFO_MMAP_VALID);
but then also:
snd_pcm_access_mask_t saccess_mask = { SND_PCM_ACCBIT_MMAP };
How should I understand this - is the intention here to disable mmap
access
or enable it?
Again, this sounds like an ALSA question?
Yes, it is an ALSA question.
In addition, there is a snd_pcm_rewindable function, but we don't use
it, and I don't know how well the different ALSA pcm types work with it.
But it seems to me like the best course of action could be to make sure
it reports the correct value for all ALSA pcm types, and then for
PulseAudio to start using it?
As I said, I will try. If this fails, we'll gain a better commit message
for this patch :)
--
Alexander E. Patrakov
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