On Wed, 2010-02-17 at 11:09 +0100, Oliver Neukum wrote:

No problem here. USB core does the mapping only if the low-level driver
so requests. The only exception is in usb_buffer_alloc(), but that boils
down to dma_alloc_coherent() 

Allright, so why do we need to "fix" anything ? Or is the whole thread
moot ? :-)

It's pretty clear that between dma_map* and subsequent unmap, the memory
is owned by the device and must not be touched by the CPU. If that is
violated, then we have a driver bug.

Cheers,
Ben.