[alsa-devel] USB Audio initialization race

Alan Stern stern at rowland.harvard.edu
Sun Sep 15 03:35:02 CEST 2013

On Sat, 14 Sep 2013, Clemens Ladisch wrote:

> Alan Stern wrote:
> > So here's my question: If the sound driver recognizes that interface B
> > is connected with interface A when B is probed, why can't it recognize
> > this fact when A is probed?  It could claim B while A's probe is
> > running.  Then the sound card would be registered with the PCM
> > component already in place.
> The sound driver already does this.

It does?  Why does the comment preceding snd_usb_audio_probe() say:

 * thus we check the usb device pointer and creates the card instance
 * only at the first time.  the successive calls of this function will
 * append the pcm interface to the corresponding card.

Is the comment out of date?

Anyway, since the driver does this, it means the scenario envisioned by
David can't happen.  Not unless the device's descriptors are buggy.

Alan Stern

More information about the Alsa-devel mailing list