[alsa-devel] Allocating buffers for USB transfers (again)

Daniel Mack zonque at gmail.com
Wed Aug 10 17:33:02 CEST 2011

On 08/10/2011 04:32 PM, Alan Stern wrote:
> Looking at the driver's current code, it appears that your patch
> does not fix the bug properly.  Using discontiguous regions in the
> transfer buffer is perfectly okay.  The real problem is later on,
> where you do:
> if (send_it) { out->number_of_packets = FRAMES_PER_URB;
> This should be
> out->number_of_packets = outframe;
> The way it is now, the USB stack will try to use data from all the
> frame descriptors, and the last few will be stale because the loop
> doesn't set them.

That's actually true, even though it doesn't seem to cause any trouble.
I tested everything here of course, and the output URBs return back from
the USB stack with their length fields zeroed out, which then
causes the stack to send packets with zero-length fields at the end.

However, doing it right doesn't harm either. Thanks for spotting.

Takashi, can you apply this version?


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