Re: linux-6.4 alsa sound broken

[Jaroslav Kysela]

On 03. 05. 23 22:00, Oswald Buddenhagen wrote:
> On Wed, May 03, 2023 at 09:32:02PM +0200, Jaroslav Kysela wrote:
> > On 03. 05. 23 18:10, Takashi Iwai wrote:
> > > The dmix uses the silence_size=boundary as a fill-all operation, and
> > > it's a free-wheel mode, so supposedly something was overlooked in your
> > > code refactoring.
> > >
> > > Could you check it and address quickly?  I'd like to fix it before
> > > 6.4-rc1 release, so if no fix comes up in a couple of days, I'll have
> > > to revert the change for 6.4-rc1.
> >
> > I would revert this patch.
>
> > It seems that this "do silence right after the playback is finished"
> > mechanism is not handled in the updated code (and I overlooked that,
> > too):
> no, there is nothing wrong with the code _per se_.
>
> what's happening is that the dmix plugin doesn't update the application
> pointer, and somehow gets away with it.

Dmix uses the free mode, because multiple applications can write to the 
buffer. We cannot do application pointer updates in the shared resource.

> anyway, this means that we need to revert the code path for top-up mode,
> which means reverting most of the patch's "meat".
> i think i can do better than your proposal, but not today anymore.

Ok, let's see. I tried to be minimalistic to fix bugs and then we can talk 
about the improvements.

> fwiw, the echo results from the plugin apparently summing up the samples
> in the buffer without clearing it first, that is, it relies on the
> auto-silencing doing the clearing, which the patch broke under the given
> circumstances. rather obvious in retrospect.

Dmix does not know which samples were updated by other applications. The 
application tracks only own samples.

						Jaroslav

--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.