thinkpad mute button not working since upgrade to stretch

[Paul Seyfert <pseyfert.mathphys@gmail.com>]

Hi,

I am using a thinkpad x220 running debian stable and enjoyed until the
upgrade to stretch that the mute button worked when waking up from
hibernate-ram already before the desktop environment was fully loaded
(especially before music players continue playback) and even when the
screen was locked.

I.e. i could send the laptop to hibernate with music playing, and if I
want the laptop to be silent when I open it, I could still rely on the
mute button.

Since I moved to stretch the mute button does not function anymore in
this way (I have assigned it with xbindkeys, but this doesn't work with
a screen lock in place).

After a short google search I tried the suggestions from the arch wiki
http://www.thinkwiki.org/wiki/Mute_button
and tried changing the line
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
to
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=!Linux"
or
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=Linux"

in /etc/default/grub
(and ran update-grub and rebooted)
without success though.

Assuming I'm not the only thinkpad user, any others around who
encountered that problem and have already found a solution? Or tips for
how to get the mute button to work hardware-like again?

Thanks in advance,

Paul