Lenovo X200 Mute button mutes with the EC, not in software
This has the side effect of only muting the speakers, and is not toggleable.
Audio playing; press mute; muted audio (OS shows volume on still); press mute; still muted audio;
This was (in the Lenovo BIOS) toggleable with an ACPI cmdline tweak to the kernel.  However when I tried this a while ago it didn't work (I presume that CB doesn't replicate this behavior).
#1 Updated by lx r over 2 years ago
The behaviour should be configurable. There are 2 bits reserved to configure this behaviour.
See bit 5-6 (count from 0) in 0x3 of the EC memory.
You can change those bits using ectool under coreboot.git/util/ectool.
dumps the whole memory (a special buffer on the EC).
Read out the byte on 0x3 and play a little bit with bit 5-6
./ectools -w 0x3 -z 0xXX