[pulseaudio-discuss] ThinkPad T-510 audio output mute LED non-workingness]

Glenn Golden gdg at zplane.com
Tue Apr 14 04:54:07 PDT 2015

David Henningsson <david.henningsson at canonical.com> [2015-04-14 13:32:42 +0200]:
> Just to check - you did press F4 or F5 to make all capture controls show up,
> right?

Yes. And I widened out the display to make sure there were no more controls
hidden on either side.

Btw, just in case it may be of interest to you or anyone else with the same
or similar issue: Attached is a "behavioral schematic" that seems to accurately
reflect the relationship between {pavucontrol/pactl} mute and the hardware
mute function and LEDs on my T-510, showing the differences across the kernel
change between 3.18 and 3.19.

The main thing to note is that in 3.18 (when the driver fielded the mute
key events itself) it appears to have handled those events by instituting
some sort of "outboard" speaker-only mute, completely independent of the
pavucontrol/pactl mute. In 3.19 of course, the mute key is not fielded 
directly by the driver any longer, it's only a userspace key. But the point
is that if the user tries to handle the key event by "pactl"ing the mute
function, it's not going to have the same effect that the driver was able
to realize by doing whatever it did with that "outboard" control (including
toggling the mute LED).

(Btw, not suggesting this diagram in any way reflects the actual circuit
topology, of which I have no knowledge; only that it seems to capture the
observed muting (and mute LED) behavior.)
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