[alsa-devel] Issues and/or possible bugs in alsa

[Yomi Ogunwumi]

Iwai, I checked the value
of /sys/module/snd_hda_intel/parameters/power_save with less, it is set to
0 already.

On Wed, Feb 25, 2015 at 3:36 AM, Alexander E. Patrakov <patrakov at gmail.com>
wrote:

> 25.02.2015 13:30, Jaroslav Kysela wrote:
>
>> Dne 25.2.2015 v 09:14 Alexander E. Patrakov napsal(a):
>>
>>> 25.02.2015 03:46, Yomi Ogunwumi wrote:
>>>
>>>> Third. This is just a question. Is this :
>>>> https://bugs.freedesktop.org/show_bug.cgi?id=86676 actually a
>>>> pulseaudio
>>>> bug, or is it an issue with alsa?
>>>> I'm only asking since Raymond linked something that seemed to belong to
>>>> the
>>>> alsa project.
>>>>
>>>>  This is a bug both in ALSA and in PulseAudio.
>>>
>>> The ALSA part (from the user viewpoint) is that the softvol plugin does
>>> not reprocess the already-submitted but buffered samples when the volume
>>> changes. But it can't, because that would require an additional thread
>>> for monitoring the software volume changes, and such thread does not
>>> exist.
>>>
>>> The PulseAudio part of the bug is that it does not deactivate softvols,
>>> even though it can apply volume in software itself. In October 2014, in
>>> Dusseldorf, a general agreement has been reached on the following
>>> arguments:
>>>
>>>    * ALSA has no API to definitely distinguish softvols from other
>>> controls.
>>>    * ALSA has the snd_ctl_elem_info_is_user() API function that tells
>>> whether this is a userspace control.
>>>    * All softvols are userspace controls.
>>>    * There are other kinds of userspace controls, but they are rare.
>>>    * If a control is named PCM Playback Volume and is a userspace
>>> control, then it's likely a softvol. Not bulletproof, but a good-enough
>>> heuristic.
>>>    * On finding a softvol, PulseAudio should set it to 100% (so that it
>>> doesn't eat CPU) and don't touch from that point on.
>>>
>>> But nobody has implemented this so far.
>>>
>> PulseAudio should open PCM with the SND_PCM_NO_SOFTVOL mode. In this
>> case, the PCM device does not add the softvol plugin to the internal
>> plugin chain. These mode flags was introduced a long time ago (discussed
>> with Lennart) and I thought that PA uses it.
>>
>>                                         Jaroslav
>
> Well, good to know, at least.

>
>>
> Well, that can be done, but the "don't attempt to control the softvol"
> part of the bug needs to be solved first. SND_PCM_NO_SOFTVOL by itself is
> not sufficient.
>
> --
> Alexander E. Patrakov
>
>


-- 
*Yomi*