Re: [PATCH v2 2/2] ALSA: pcm: auto-fill buffer with silence when draining playback

[Oswald Buddenhagen <oswald.buddenhagen@gmx.de>]

On Fri, Apr 21, 2023 at 11:33:35AM +0200, Jaroslav Kysela wrote:
>On 20. 04. 23 13:33, Oswald Buddenhagen wrote:
>> Draining will always playback somewhat beyond the end of the filled
>> buffer. This would produce artifacts if the user did not set up the
>> auto-silencing machinery, which is an extremely easy mistake to make, as
>> the API strongly suggests convenient fire-and-forget semantics. This
>> patch makes it work out of the box.
>
>NACK. The initial implementation should be put to alsa-lib as discussed.
>
as discussed, a user-space only implementation based on the current 
kernel api is not reasonable:
it could either enable auto-silencing on device open (which would be 
unreasonably expensive) or it could enable it on drain (and disable it 
once draining is done, which would be unreasonably complex due to 
needing to handle asynchronous draining completion).

so we would at least need a kernel api to enable silence-on-drain, which 
user space could apply on device open.
this would be easy enough to do, but i really don't see a point in 
adding that complexity, given that it should be always enabled, lest it 
won't have much of a real-world impact.

fwiw, i just realized that the argument against touching the mmap'd 
buffer is even weaker with the updated implementation, as it only clears 
as much as user space would have to clear anyway (pedantically, i could 
round it down to the end of a period rather than filling two whole 
periods, if that's the bit that convinces you).

regards