I investigated this further on ASUS ExpertBook PM3406CHA with:
Codec: Realtek ALC256
Vendor ID: 0x10ec0256
Subsystem ID: 0x10431664
Kernel tested: 7.2.6-arch2-1
Windows previously produced normal speaker output on this hardware.
On a fresh Linux boot the internal speakers are silent, although ALSA/PipeWire
routing is correct and an active PCM stream reaches ALC256 DAC node 0x02.
Fresh-boot Realtek coefficient 0x10 is:
0x1d20
I experimentally reduced a larger PM3406CHA codec initialization sequence to
one required change.
Starting from a fresh reboot, with speaker-test already running and silent,
executing only:
hda-verb /dev/snd/hwC1D0 0x20 0x500 0x10
hda-verb /dev/snd/hwC1D0 0x20 0x400 0x7f20
immediately restores internal-speaker output.
No volume/mixer change is required at that point.
I separately eliminated the following from the speaker fix:
GPIO2 changes
speaker/headphone EAPD changes
headphone pin-control changes
coefficients 0x06, 0x16, 0x1b, 0x23, 0x30, 0x35,
0x37, 0x45, 0x46 and 0x49
A boot-time userspace workaround applying only coef 0x10=0x7f20 has also been
verified across a reboot.
Suspend -> resume retains working audio without reapplying the
workaround.
This therefore appears suitable for an ALC256 machine quirk for subsystem
1043:1664 which registers:
{ 0x20, AC_VERB_SET_COEF_INDEX, 0x10 },
{ 0x20, AC_VERB_SET_PROC_COEF, 0x7f20 },
I have a candidate alc269.c patch implementing this.
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https://bugs.launchpad.net/bugs/2162718
Title:
No sound from internal speakers on ASUS ExpertBook P3 (PM3406CHA) -
Realtek ALC256, subsystem 1043:1664 not covered by existing fix
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