Problem with non aligned DMA in usbnet on ARM

On Wed, Aug 11, 2010 at 08:54:27AM -0700, Gary King wrote:

On 08/11/2010 04:38 AM, Martin Fuzzey wrote:

quoted

It seems to me these fixup functions are not intended to solve
alignment issues but rather implement device specific framing (such as
when the hardware packs multiple ethernet frames into a single urb)

I sent a patch to the list about 2 weeks ago that added support to
DMA bounce to bounce for misaligned buffers. We have a similar
problem with URB alignment for usbnet on Tegra's HCD:

http://lists.arm.linux.org.uk/lurker/message/20100729.005746.b43fa1d9.en.html

We don't want to add support for this to DMA bounce.  DMA bounce is already
a pain in the backside and causes its own set of problems - please let it
die a long slow but quite death.

If you want to see the kind of pain dmabounce causes, look at this long
standing and as yet unsolved bug:

  http://bugzilla.kernel.org/show_bug.cgi?id=7760