i have the same issue with a thinkpad t400. as suggested elsewhere, updating the bios and adding the boot option acpi_osi="Linux" fixes the issue. both mute and unmute works and i get the correct OSD. however, since i don't really know what other things the acpi_osi="Linux" boot option alters i'm reluctant to use it.
i have the same issue with a thinkpad t400. as suggested elsewhere, updating the bios and adding the boot option acpi_osi="Linux" fixes the issue. both mute and unmute works and i get the correct OSD. however, since i don't really know what other things the acpi_osi="Linux" boot option alters i'm reluctant to use it.