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[Bug 1882787] [NEW] AUD_set_volume_out takes SWVoiceOut as parameter, b
From: |
malib69055 |
Subject: |
[Bug 1882787] [NEW] AUD_set_volume_out takes SWVoiceOut as parameter, but controls HWVoiceOut |
Date: |
Tue, 09 Jun 2020 14:18:12 -0000 |
Public bug reported:
There was a change in
https://github.com/qemu/qemu/commit/571a8c522e0095239598347ac0add93337c1e0bf
#diff-230ab01fa7fb1668a1e9183241115cb0R1852-R1853 (audio/audio.c) which
breaks audio output on devices which have multiple software voices on
the same hardware voice.
When multiple software voices use the same hardware voice, then setting
a volume / mute for any of the software voices, will affect all other
software voices, too.
I'm not sure if such a use-case exists in QEMU; however, it does exist in my
fork.
It's also easy to see that this is a bug in the QEMU audio subsystem.
The API (and broken function) for this is:
```
void AUD_set_volume_out (SWVoiceOut *sw, int mute, uint8_t lvol, uint8_t
rvol)
```
So this is supposed to modify the SWVoiceOut.
However, if the backend supports `pcm_ops->volume_out` this does not
work as expected. It's always as if you had called:
```
void AUD_set_volume_out (HWVoiceOut *hw, int mute, uint8_t lvol, uint8_t
rvol)
```
*(Note how this modifies the hardware voice)*
In my specific use case, I have 2 outputs (digital and analog audio on AC97),
and I want to mute the digital audio output, but I still need to keep the voice
activated for timing.
However, if I mute the digital audio SWVoiceOut, it will also affect the other
SWVoiceOut (for analog audio) on the same HWVoiceOut.
---
Old code - if the hardware supports volume changes, it will receive the
software voice which should be modified, so changes can be restricted to
that one voice:
```
HWVoiceOut *hw = sw->hw;
[...]
if (hw->pcm_ops->ctl_out) {
hw->pcm_ops->ctl_out (hw, VOICE_VOLUME, sw);
}
```
New code - the hardware backend will have no way to differentiate
software voices; so any change will affect all voices. The volume which
was set last on any sw voice will set a global volume / mute for all
voices on the hardware backend:
```
HWVoiceOut *hw = sw->hw;
[...]
if (hw->pcm_ops->volume_out) {
hw->pcm_ops->volume_out(hw, &sw->vol);
}
```
The old interface was already broken with some (all?) backends, because they
ignored the software voice, but at least the design made sense.
However, the new design is fundamentally broken because it doesn't even tell
the backend which voice is supposed to be modified.
---
Bug was introduced in cecc1e79bf9ad9a0e2d3ce513d4f71792a0985f6
The affected code was touched since then, but still remains in
49ee11555262a256afec592dfed7c5902d5eefd2
** Affects: qemu
Importance: Undecided
Status: New
** Tags: audio subsystem voice
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1882787
Title:
AUD_set_volume_out takes SWVoiceOut as parameter, but controls
HWVoiceOut
Status in QEMU:
New
Bug description:
There was a change in
https://github.com/qemu/qemu/commit/571a8c522e0095239598347ac0add93337c1e0bf
#diff-230ab01fa7fb1668a1e9183241115cb0R1852-R1853 (audio/audio.c)
which breaks audio output on devices which have multiple software
voices on the same hardware voice.
When multiple software voices use the same hardware voice, then
setting a volume / mute for any of the software voices, will affect
all other software voices, too.
I'm not sure if such a use-case exists in QEMU; however, it does exist in my
fork.
It's also easy to see that this is a bug in the QEMU audio subsystem.
The API (and broken function) for this is:
```
void AUD_set_volume_out (SWVoiceOut *sw, int mute, uint8_t lvol, uint8_t
rvol)
```
So this is supposed to modify the SWVoiceOut.
However, if the backend supports `pcm_ops->volume_out` this does not
work as expected. It's always as if you had called:
```
void AUD_set_volume_out (HWVoiceOut *hw, int mute, uint8_t lvol, uint8_t
rvol)
```
*(Note how this modifies the hardware voice)*
In my specific use case, I have 2 outputs (digital and analog audio on AC97),
and I want to mute the digital audio output, but I still need to keep the voice
activated for timing.
However, if I mute the digital audio SWVoiceOut, it will also affect the
other SWVoiceOut (for analog audio) on the same HWVoiceOut.
---
Old code - if the hardware supports volume changes, it will receive
the software voice which should be modified, so changes can be
restricted to that one voice:
```
HWVoiceOut *hw = sw->hw;
[...]
if (hw->pcm_ops->ctl_out) {
hw->pcm_ops->ctl_out (hw, VOICE_VOLUME, sw);
}
```
New code - the hardware backend will have no way to differentiate
software voices; so any change will affect all voices. The volume
which was set last on any sw voice will set a global volume / mute for
all voices on the hardware backend:
```
HWVoiceOut *hw = sw->hw;
[...]
if (hw->pcm_ops->volume_out) {
hw->pcm_ops->volume_out(hw, &sw->vol);
}
```
The old interface was already broken with some (all?) backends, because they
ignored the software voice, but at least the design made sense.
However, the new design is fundamentally broken because it doesn't even tell
the backend which voice is supposed to be modified.
---
Bug was introduced in cecc1e79bf9ad9a0e2d3ce513d4f71792a0985f6
The affected code was touched since then, but still remains in
49ee11555262a256afec592dfed7c5902d5eefd2
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1882787/+subscriptions
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