lkml.org 
[lkml]   [2014]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [alsa-devel] [PATCH v2 5/6] sound/usb: pcm changes to use media token api
On 10/22/2014 01:45 PM, Devin Heitmueller wrote:
>> this seems like a feature, not a bug. PulseAudio starts streaming before
>> clients push any data and likewise keeps sources active even after for some
>> time after clients stop recording. Closing VLC in your example doesn't
>> immediately close the ALSA device. look for module-suspend-on-idle in your
>> default.pa config file.
>
> The ALSA userland emulation in PulseAudio is supposed to faithfully emulate
> the behavior of the ALSA kernel ABI... except when it doesn't, then it's not
> a bug but rather a feature. :-)
>
>> I also agree that the open/close of the alsa device is the only way to
>> control exclusion.
>
> I was also a proponent that we should have fairly coarse locking done
> at open/close for the various device nodes (ALSA/V4L/DVB). The challenge here
> is that we have a large installed based of existing applications that
> rely on kernel
> behavior that isn't formally specified in any specification. Hence
> we're forced to try
> to come up with a solution that minimizes the risk of ABI breakage.
>
> If we were doing this from scratch then we could lay down some hard/fast rules
> about things apps aren't supposed to do and how apps are supposed to respond
> to those exception cases. Unfortunately we don't have that luxury here.
>

Sounds like we don't have a clear direction on open/close or capture
start/stop. What I am hearing is open/close isn't acceptable for
media maintainers and capture trigger start/stop isn't acceptable
to sound maintainers. :) Fork in the road, which way do we go?

Implementation wise, supporting capture trigger start/stop approach
will be harder to maintain in longterm. It adds more variables to
the mix. Applications open sounds device from the main thread and
then create a new thread to handle streams. I can see that based
on the token hold requests that come in. So the token hold logic
will have to take that into account, leading into potential
unbalanced lock/unlock scenarios. It is not impossible to solve,
that's what I did in this patch series, but it does get complex.

What I am looking for is some consensus on let's go with an approach
and try. Doesn't matter which way we go, and how much testing I do,
I am bound to miss something and this work needs to soak for a bit in
the media experimental branch.

thanks,
-- Shuah



--
Shuah Khan
Sr. Linux Kernel Developer
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978


\
 
 \ /
  Last update: 2014-10-24 17:21    [W:0.124 / U:0.420 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site