How to annotate USB jacks without jack detection?

[Takashi Iwai]

On Fri, 11 Dec 2020 08:14:24 +0100,
Kai-Heng Feng wrote:
> 
> Hi,
> 
> There are some UAC1 devices come with jacks, but without jack
> detection ability. And many USB/Thunderbolt docks are equipped with
> such USB device.
> 
> Userspace like PulseAudio automatically switch to USB audio when they
> gets plugged. However, auto-switching to UAC1 device can be
> problematic because it may not connected to any headset or speaker.
> 
> So I wonder what's the best way to let userspace know the USB device
> is a jack without jack detection ability? Through sysfs or dedicated
> UCM conf?

It's a good question.  AFAIK, that's a long-standing problem, and most
of such devices provide the jack detection via HID, which is,
obviously, a completely different driver.  So, if HID driver actually
creates input devices, we'd need to associate them with the sound card
somehow (likely in user-space).  But I have no clear idea what's the
best approach yet.

Also, I'm not sure whether HID device really gives the right jack
detection event.  A cheap UAC1 device I have here doesn't seem to give
the jack detection but only the mute/volume events, as it seems...

OTOH, there are some UAC2 devices providing the jack detection in the
USB-audio interface, and they seem work as is of now.


thanks,

Takashi