[alsa-devel] [PATCH v4 09/15] ALSA: usb-audio: conditional interface altsetting

[Takashi Iwai]

At Mon, 07 Oct 2013 20:23:38 +0200,
Clemens Ladisch wrote:
> 
> Eldad Zack wrote:
> > On Mon, 7 Oct 2013, Takashi Iwai wrote:
> >> Eldad Zack wrote:
> >>> On some devices, if the endpoint for the other direction is in use,
> >>> setting one interface will shutdown the other (in use) endpoint.
> >>> This patch moves all of the alternate setting operations for pcm
> >>> ops to one function which checks if we can do so.
> >>>
> >>> If current alternate is 0, it is safe to set.
> >>
> >> Is this check needed for all devices?
> >
> > I'm not sure, I only have this one device to test with.
> 
> In theory, interfaces are independent, but in practice, the firmware
> does whatever it does.  For implicit feedback devices, it's likely that
> they were expected to be used in full duplex mode only.

For the implicit feedback devices, I find the change being good, too.
But my concern is rather that this filtering is applied to all cases,
no matter whether it's implicit fb or not.  In such cases, the
assignment of full duplex streams is just casual, and they are likely
individual.


thanks,

Takashi