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

[Torstein Hegge]

On Wed, Mar 27, 2013 at 12:52:14 +0100, Daniel Mack wrote:
> On 27.03.2013 12:47, Torstein Hegge wrote:
> > 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.
> 
> You could just try and catch that currently unhandled interrupt. We
> should support that anyway at some point ...

It doesn't look like snd_usb_mixer_interrupt_v2() is invoked on sample
rate changes. As far as I can tell, that should be invoked on any
interrupts, but it was never triggered, so I might be wrong.


Torstein