[alsa-devel] Jack sensing in snd_usb_audio ?

[Bastien Nocera]

On Tue, 2016-10-18 at 14:07 +0200, Takashi Iwai wrote:
> On Wed, 12 Oct 2016 18:15:04 +0200,
> Bastien Nocera wrote:
> > 
> > On Wed, 2016-10-12 at 18:06 +0200, Clemens Ladisch wrote:
> > > Bastien Nocera wrote:
> > > > On Wed, 2016-10-12 at 14:43 +0200, Clemens Ladisch wrote:
> > > > > Bastien Nocera wrote:
> > > > > > "
> > > > > > A change of state in the audio function is most often
> > > > > > caused by
> > > > > > a
> > > > > > certain event that takes place. An event can either be
> > > > > > user-
> > > > > > initiated
> > > > > > or device-initiated. User-initiated jack insertion or
> > > > > > removal
> > > > > > is a
> > > > > > typical example of a user-initiated event.
> > > > > > "
> > > > > 
> > > > > 
> > > > > There are not many USB Audio 2.0 devices, and I'm not aware
> > > > > of
> > > > > any
> > > > > that actually implements this.
> > > > 
> > > > 
> > > > I guess I would see whether there are events if I captured the
> > > > USB
> > > > traffic even without special handling/turning on a feature in
> > > > the
> > > > drivers, right?
> > > 
> > > 
> > > Most devices do not even have the status endpoint (see "lsusb
> > > -v").
> > > To check what events arrive, you can add logging to the
> > > snd_usb_mixer_interrupt() function.
> > 
> > I'm guessing it doesn't support it then (see attached log)
> 
> So this looks like a HID, not from the audio device class.
> It's an oft-seen implementation.
> 
> > I also checked the input device output when plugging in something,
> > with
> > evtest, and no feedback either.
> 
> Then at first you need to hack a HID driver to support this device.
> It'll create an input device, and then we'll need to find some way to
> couple the given input device and the audio device.  We can parse the
> sysfs device path to figure out, but I'm not sure what's the best way
> to tell it to applications.

You misunderstood. There's no input events on the input device, there's
also no hidraw events (hid-recorder didn't see any events) and using
usbmon also got me no USB events whatsoever when plugging or unplugging
a jack on either the headphones or the microphone jack.

So there's really nothing that we can do for this hardware. Shame, it
would have been pretty useful to me :)

Thanks all for your help