[alsa-devel] Jack event API - decision needed
david.henningsson at canonical.com
Wed Jun 22 12:47:35 CEST 2011
On 2011-06-21 14:39, Mark Brown wrote:
> On Tue, Jun 21, 2011 at 02:11:15PM +0200, David Henningsson wrote:
>> On 2011-06-21 01:40, Mark Brown wrote:
>>> Oh, then in that case we've got another issue in that jacks that happen
>>> not to be associated directly with a sound card for some reason (they're
>>> implemented by the embedded controller and exposed via ACPI for example)
>>> won't be made available to applications.
>> Which is not a problem IMO, because in the desktop world this does
>> not happen (or at least I've never seen it), and in the embedded
>> world you have PA running as root anyway.
> This seems rather short sighted - the desktop and embedded worlds aren't
> as clearly divided as all that, you've already got things like the
> Genesi systems on the market at the minute running Ubuntu on ARM
> hardware for example and you've also got a bunch of laptop manufacturers
> putting ARM systems in their systems to dual boot into.
If you have a better idea about how to determine if a SW_VIDEOOUT jack
is actually an audio jack or not, let me know.
>>> OK, well that doesn't seem like an immediately obvious choice. I can
>>> imagine there might be some concern around keyboards due to passwords
>>> but in general it doesn't seem obvious that the console user shouldn't
>>> be able to read physical input devices on the box (which is the case
>>> we're trying to implement here; we don't need write support). Do all
>>> classes of input device currently have some root only service to mediate
>>> access to them, and if that is the model we're using perhaps it'd make
>>> sense to have one for this with a dbus interface or whatever that
>>> PulseAudio can talk do rather than to have it talking direct to the
>> If I look at what /dev/input devices I have here, that's keyboard,
>> mouse, and ACPI buttons (power, lid close etc). AFAIK, all of those
>> go through the X input layer. Play/pause keys should go through
>> there as well, but are you saying that audio jack events should also
>> go through the X input layer?
> I'm asking what the sensible model for handling this stuff is and why we
> need to use a different model for this. Perhaps this should go through
> the X server, perhaps somewhere else.
> It does strike me that the UI may want to be able to join the buttons up
> with the particular jack - for example, if you've got a headset that
> you've got assigned to telephony functions only perhaps the mic short
> button on that headset should only do telephony things.
>> If you are, you're welcome to try to fit it in the 248 keycodes that
>> are already occupied, design a new X input extension, or whatever is
>> the right solution for that. I don't know myself.
>> If you're not, then that's why this is specific to audio.
> It doesn't strike me as an obviously awful solution if that's what we're
> using for things like the ACPI buttons which seem pretty similar - like
> I say one of my questions here is why we need to do something domain
> specific here. There are certainly a bunch of other switch types in the
> input API which look like the desktop might want to look at them (things
> like SW_DOCK and SW_ROTATE_LOCK for example) so presumably we ought to
> handle them somehow too.
> It does sound like we need some input from the udev and more general
> userspace stack people about how this stuff is usually handled.
I was hoping for Lennart or Kay to answer here as they are more "udev
and general userspace stack people" than I am, but lacking that, I can
only notice that on my machine, the only processes listening to
/dev/input files are upowerd (for the lid switch) and Xorg (for
everything else).  Acpid seems to be able to listen to these events
too, but does not seem to do that on my machine (as determined by "sudo
Xorg can only handle keypresses and mouse events, and AFAICT don't care
about switch events, so, if the way things are usually handled is to add
another u-audiojack-d just to forward events to pulseaudio, I would
prefer giving the user access to the relevant input devices directly,
out of pure simplicity.
David Henningsson, Canonical Ltd.
 On a slightly older machine there is also hald-addon-input, but
since that's deprecated, let's ignore that for now.
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