Comment 125 for bug 357673

On Wed, 04 Nov 2009, Charles Profitt wrote:
> T42p -- mute, vol up, vol down all work.
> T61p -- mute, vol up, vol down all work.
> T500 -- vol up, vol down work. mute has no display and only mutes -- it does not un-mute as the second press does on the other two models.

Because no ThinkPad should unmute by a second press. The T500 behaviour is
correct, while the T42p/T61p behaviours are syntethic, and done in
userspace.

The weird thing is that someone reported to me the T500 did it the weird way
(second press unmutes) because it had a direct way for the user to see if it
is mute/unmute (a LED). It may depend on OSI(Linux) -- check kernel ACPI
documentation to know what I am talking about -- and it is likely a somewhat
bad idea to mess with OSI just because of the Volume keys... enable
OSI(Linux), and you have to test _everything_ for regressions, even
processor power management control, power draw while sleeping and after
shutdown(!), etc.

> The behavior on the T500 = press vol up or vol down and OSD displays the
> message properly, press mute and the sound is muted with no OSD message
> displayed, if mute is pressed while the sound is muted it does not
> restore sound.

Which is good. It means you have a button that _always_ kills sound, and
two buttons that always help sound output (vol up/down). You are always
sure of what will happen when you press the buttons, regardless of the
current state of the audio mixer or presence of OSD.

This means you can hastly press mute as many times as you want to make sure
the ThinkPad won't utter a peep in an embarassing situation. This is valid
for the T42, that has no visual clue of the mute state, and I believe the
T61p doesn't have mute LEDs either. Models with a mute LED could operate
in either way, it depends wheter you are going to ignore the blind, and
whether a blind person would ever want to mute sound. Since they usually
don't mute sound, I did not raise a major stink when people started messing
with the way mute works.

> The behavior on the T42p and T61p is that mute, vol up, vol down display
> a message using OSD and the second press on the mute button restores
> sound.

This is caused by userspace. The firmware doesn't like it much, btw.

--
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh