[alsa-devel] [PATCH v5] ALSA: usb: Work around CM6631 sample rate change bug

Torstein Hegge hegge at resisty.net
Wed Mar 27 12:47:03 CET 2013

On Wed, Mar 27, 2013 at 11:09:01 +0100, Clemens Ladisch wrote:
> Torstein Hegge wrote:
> > The C-Media CM6631 USB receiver doesn't respond to changes in sample rate
> > while the interface is active. The same behavior is observed in other UAC2
> > hardware like the VIA VT1731.
> Might it be possible that these devices have reset the interface (see
> UAC2 section 3.16.3), and that the driver hasn't noticed this because it
> doesn't handle Active Alternate Setting Control interrupts?

If that was the case, wouldn't the device be in altsetting zero after
the sample rate set and not be able to output sound at all? And as long
as the current altsetting supports the target sample rate as reported in
/proc/asound/card1/stream0, Active Alternate Setting Control shouldn't
have to be invoked.


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