kern/59712: hdaudio driver exposes nonexistent volume controls

[nia%pkgsrc.org@localhost]

>Number:         59712
>Category:       kern
>Synopsis:       hdaudio driver exposes nonexistent volume controls
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 19 13:15:00 +0000 2025
>Originator:     nia
>Release:        any with hdaudio
>Organization:
The SliderBSD Foundation
>Environment:
>Description:
My audio chipset (and indeed any realtek chipset that i've seen)
has mute-only output amplifier controls:

[     1.044129] hdaudio1 at pci7 dev 0 function 4: HD Audio Controller
[     1.044129] hdaudio1: interrupting at msi6 vec 0
[     1.044129] hdaudio1: HDA ver. 1.0, OSS 4, ISS 4, BSS 0, SDO 1, 64-bit
[     1.044129] hdafg1 at hdaudio1: Realtek ALC897
[     1.044129] add ctrl outamp mute=0 step=87 size=2 offset=87
[     1.044129] add ctrl outamp mute=0 step=87 size=2 offset=87
[     1.044129] add ctrl outamp mute=0 step=87 size=2 offset=87
[     1.044129] add ctrl outamp mute=0 step=87 size=2 offset=87
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=1 step=0 size=0 offset=0
[     1.044129] add ctrl outamp mute=0 step=87 size=2 offset=87

These are the ones with step=0 and size=0.

Currently the way the driver tries to handle these is quite odd.
It creates a normal mute control, but also creates a volume control
with delta=256 (i.e. not possible to modify). This clutters up
mixer interfaces and i've had to put a workaround for this in aiomixer.

The code contains some hacky workarounds for these fake controls,
e.g.:

if (ctl->ctl_step == 0)
        divisor = 128; /* ??? - just avoid div by 0 */
else
        divisor = 255 / ctl->ctl_step;
        
hdafg_control_amp_set(ctl, HDAUDIO_AMP_MUTE_NONE,
  mc->un.value.level[AUDIO_MIXER_LEVEL_LEFT] / divisor,
  mc->un.value.level[AUDIO_MIXER_LEVEL_RIGHT] / divisor);
>How-To-Repeat:
run mixerctl -la on a machine with realtek audio hardware
>Fix:
The way that `hdafg_build_mixers` is written means that volume-only
controls (with no mute) are possible, but mute-only controls with
no volume are not possible. This restriction does not come from any
particular API or specification, it's just a quirk of the driver.

The driver should be modified to build only mute enums for those
mute-only controls.

I should get around to this.