This issue appears to have been discussed several times on this forum, but to my knowledge there has been no resolution, only some workarounds. The issue is that memory mapped UVC streaming YUYV video works ONLY if USB DMA is disabled (CONFIG_MUSB_PIO_ONLY=y). I have tried this on multiple kernels up to 3.2.13 with the same results. My test program is the simple example program from the V4L2 specification:
This same program appears to work fine on the Beaglebord xM.
As the bone is significantly slower than the xM CPU load is more of an issue and therefore DMA operation is even more desirable.
Enabling DMA seems to work fine with applications including USB attached storage. It is only video streaming that appears to be affected.
Any suggestions would be very welcome.