[PATCH] Add duplex sound support for USB devices using implicit feedback

[Takashi Iwai]

On Sun, 10 May 2020 20:29:11 +0200,
Erwin Burema wrote:
> 
> For USB sound devices using implicit feedback the endpoint used for this feedback should be able to be opened twice, once for required feedback and second time for audio data. This way these devices can be put in duplex audio mode. Since this only works if the settings of the endpoint don't change a check is included for this.
> 
> This fixes bug 207023 ("MOTU M2 regression on duplex audio") and should also fix bug 103751 ("M-Audio Fast Track Ultra usb audio device will not operate full-duplex")
> 
> Signed-off-by: Erwin Burema <e.burema at gmail.com>

Applied now to for-next branch.  Thanks!


Takashi