Problem with non aligned DMA in usbnet on ARM

Russell King - ARM Linux linux at
Wed Aug 11 16:35:05 EDT 2010

On Wed, Aug 11, 2010 at 08:54:27AM -0700, Gary King wrote:
> On 08/11/2010 04:38 AM, Martin Fuzzey wrote:
> > 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:

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:

More information about the linux-arm-kernel mailing list