Hi Andrew and thanks for dealing with this issue! I'm sometimes working
with certifying Lenovo for Canonical/Ubuntu, so this definitely concerns
me. However I know very little about the thinkpad-acpi driver and would
like to know more about how it works, and especially the mixer part.
On 2011-05-23 19:21, Andrew Lutomirski wrote:
Most ThinkPad laptops have an extra mixer that has nothing to do with
the HDA audio hardware. The kernel can talk to it through the
embedded controller and, if it's muted, then there's no sound even if
the normal controls are all set on.
Does this concern the internal speaker only, or headphones / line out as
well? Or can that differ between models? I'm assuming it doesn't mute e
g USB headset or audio out over HDMI.
These laptops have three special buttons. The mute button either
mutes the mixer or toggles the mute state. The volume up button
unmutes the mixer (if muted) and sends KEY_VOLUMEUP. The volume down
button unmutes the mixer and sends KEY_VOLUMEDOWN.
On very new models, there's a hardware mute light that indicates the
status of the hardware mute.
The thinkpad-acpi driver currently exposes an ALSA mixer and the
alsamixer utility can talk to it. But PulseAudio ignores it
completely.
What is the kernel supposed to do to get PulseAudio to DTRT?
Seen from my perspective, and maybe along the lines of Colin's reply, I
think the best would be to try to integrate the hw mute in the HDA card
at the kernel level (and thus skip card 29 entirely).
On some,
but not (I think) all, models, we can disable hardware mixer control
and make all of the buttons act like ordinary buttons, but that will
cause the light (if present) to malfunction, and I don't know if all
models can do this. So as it stands, PulseAudio would have to
understand that the mixer is special and watch for ALSA change
notifications.
So, what can the thinkpad-acpi driver do here? Can it e g control the
hardware mute status at all, or can that only be done by pressing the keys?
I'm willing to change the thinkpad-acpi driver to make it work better,
but I know nothing at all about PulseAudio internals. What should I
do?
(There's an added complexity. Really old models have mute and volume.
I don't own one, so I don't know much about how they work.)
As a maybe unrelated issue, many of these thinkpads also have a
microphone mute hotkey I was hoping to be able to get to work at some
point. Assuming we add a new key to linux/input.h, would it be easy for
you to fix that in the thinkpad-acpi driver? I think it currently
triggers KEY_UNKNOWN.
--
David Henningsson, Canonical Ltd.
http://launchpad.net/~diwic
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