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

[Raymond Yau]

>> 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.

You can use snd_ctl_elem_info_is_use() to find out the name of those user
space controls of the card and ignore those softvol "PCM playback volume"
and "Digital Capture Volume" controls

>  * 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.
>
> The relevant code can be placed in the src/modules/alsa/alsa-mixer.c file
in PulseAudio source tree. I guess that element_probe() is a good place. If
you know C programming, a contribution would be welcome.||
>

state.Generic {
control.1 {
iface CARD
name 'HDMI/DP,pcm=3 Jack'
value false
comment {
access read
type BOOLEAN
count 1
}
}
control.2 {
iface MIXER
name 'IEC958 Playback Con Mask'
value
'0fff000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
comment {
access read
type IEC958
count 1
}
}
control.3 {
iface MIXER
name 'IEC958 Playback Pro Mask'
value
'0f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
comment {
access read
type IEC958
count 1
}
}
control.4 {
iface MIXER
name 'IEC958 Playback Default'
value
'0400000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
comment {
access 'read write'
type IEC958
count 1
}
}
control.5 {
iface MIXER
name 'IEC958 Playback Switch'
value true
comment {
access 'read write'
type BOOLEAN
count 1
}
}
control.6 {
iface PCM
device 3
name ELD
value ''
comment {
access 'read volatile'
type BYTES
count 0
}
}
control.7 {
iface PCM
device 3
name 'Playback Channel Map'
value.0 0
value.1 0
value.2 0
value.3 0
value.4 0
value.5 0
value.6 0
value.7 0
comment {
access 'read write'
type INTEGER
count 8
range '0 - 36'
}
}
control.8 {
iface MIXER
name 'PCM Playback Volume'
value.0 184
value.1 184
comment {
access 'read write user'
type INTEGER
count 2
range '0 - 255'
tlv '0000000100000008ffffec1400000014'
dbmin -5100
dbmax 0
dbvalue.0 -1420
dbvalue.1 -1420
}
}
}

It is strange that your hdmi card have a softvol control ,

Was  the softvol control created when you swap the card number by index=1,0
?
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