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

Henrique de Moraes Holschuh hmh at hmh.eng.br
Sat Apr 25 08:11:59 PDT 2015

On Fri, Apr 24, 2015, at 22:39, Glenn Golden wrote:
> in response to the event.  What action can be taken to turn on the mute LED?
> Issue an amixer/pactl/pacmd command to toggle the Master Playback mute state?

Speaking as the thinkpad-acpi driver maintainer: Keeping the ThinkPad MUTE LED states in sync is the kernel's job. This is the beginning and the end of it.

It clearly is not working properly right now.  Possibly the defect is restricted to some thinkpads: Lenovo changes firmware behaviour sometimes. They're good about leaving a knob you can set to get whatever behaviour you want/need.  They're not always that good about _testing_ it, though.  And we (kernel side) are not that good at either knowing the behaviour exists, or making use of it.

Or it might be a simple driver bug that affects every thinkpad with a mute LED. I hope so, because that's much easier to fix.

Those are the facts.  It doesn't look like there is anything pulse-audio related in this issue:  it is a matter for the kernel to fix. Either in the ALSA sublayer, if it is not being able to correctly signal thinkpad-acpi to change Mute LED state, or in thinkpad-acpi if it is not correctly relaying to the thinkpar firmware the desired mute LED state.

> No, that won't do it, because the LED isn't following the mixer mute state
> (see earlier posts in this thread).  Directly access the LED via some exposed
> interface to it?  No sign that any such any such interface is available in
> /proc/acpi or /sys/class/leds (see comment #15 in the kernel bugtracker).

And it is not going to be made available (in some thinkpads, it cannot even be done: when you change the hardware mute gate state, the EC updates the LED state to match).  This is why we will consider any mute led misbehavior to be a kernel issue, to be fixed in the kernel.

> As I mentioned on the kernel bugtracker, I'm going to take this up with the
> thinkpad ACPI folks, see if they have any suggestions.

I lack the hardware to develop-and-test a fix (I am long overdue for a replacement thinkpad, really. I only have a good T43, and a damaged R60), but I am open to help (and ACK kernel-side patches).

  "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

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