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

David Henningsson david.henningsson at canonical.com
Mon Mar 30 23:43:04 PDT 2015

On 2015-03-31 05:51, Hui Wang wrote:
> On 03/31/2015 05:54 AM, Glenn Golden wrote:
>> HW: ThinkPad T-510, x86_64
>> SW: Arch Linux (synched within a week) kernel = 3.19.2, PA 6.0
>> On the above setup, the mic mute function (invoked via pavucontrol)
>> works as
>> expected: Click the mute icon, it mutes the mic input, indicates the
>> muted
>> state by greying out the pavucontrol mic gain control, and illuminates
>> the
>> little LED on the mic mute button.
>> But the analogous functionality for muting audio output only does the
>> first two things, and has no effect on the mute LED. (The LED is
>> always off.)
>>  From googling around, I'm pretty sure that these two particular LEDs
>> are not
>> directly under user control (e.g. via ACPI) but are somehow bound to the
>> mute/unmute functionality in the snd-hda-intel driver. This
>> understanding is
>> based on kernel posts like this:
>>      https://bugzilla.kernel.org/show_bug.cgi?id=49391
>> and other similar ones.
>> Before filing a ticket with the kernel guys, wanted to ask if this
>> function-LED binding is in any way under control of pulseaudio itself?
>> In other words, I guess what I'm asking is whether pulseaudio just tells
>> the driver to "mute the audio", and the driver sets the LED state
>> accordingly,
>> or whether pulse tells the driver separately to "mute the audio" and also
>> "turn on the LED".
> According to my understanding, it should be the former one,  PA tells
> the driver to "mute the audio", and the driver sets the LED accordingly.

Yes, this is correct. More specific, the mic mute LED reflects the state 
of the "Capture Switch" mixer control (mic mute LED lit when "Capture 
Switch" is off), and the mute LED reflects the state of the "Master 
Playback Switch" (mute LED lit when "Master Playback Switch" is off).

Any discrepancy of the above would be a kernel bug.

David Henningsson, Canonical Ltd.

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