On Wed, Oct 07, 2020 at 02:21:43PM +0200, Tomasz Figa wrote:

My initial feeling is that it should work, but we'll give you a
definitive answer once we prototype it. :)

We might actually give it a try in the USB HCD subsystem as well, to
implement usb_alloc_noncoherent(), as an optimization for drivers
which have to perform multiple random accesses to the URB buffers. I
think you might recall discussing this by the way of the pwc and
uvcvideo camera drivers.

Yes.  I guess for usb the dma_alloc_noncoherent as-is in linux-next
might be better.   So if you have the cycles please prototype it
either way, although for that we'd also need at least a
mmap_noncoherent method, and probaby a get_sgtable_noncoherent one.