On Tue, 27 Nov 2007 09:16:07 -0800
"H. Peter Anvin" [off-list ref] wrote:

Stephen Hemminger wrote:

quoted

Herbert Xu wrote:

quoted

On Sat, Nov 24, 2007 at 02:49:36PM +0100, Johannes Berg wrote:
 

quoted

Right. I just didn't think that would be a valid value for an
architecture to set.
    

OK.  Let me clarify this a bit more.  We require at least one
of the following rules to be met:

* the IPv4/IPv6 header is aligned by 8 bytes on reception;
* or the platform provides unaligned exception handlers.

So if your platform violates both rules then it won't work with
the IP stack, simple as that.  Fortunately I don't think such a
platform exists currently on Linux.

Cheers,
  

Then what about hardware that can't dma ethernet to non-aligned address.
Sky2 hardware breaks if DMA is not 8 byte aligned.  IMHO the IP stack 
should handle any alignment, and do the appropriate memove if the CPU requires 
alignment.

I wrote a patch for the IP stack to realign packets if necessary at one 
point.  I should dredge it up again and submit it for collective flamage.

	-hpa

Is there any standard kernel config define for "this platform can't do
unaligned accesses"?

-- 
Stephen Hemminger [off-list ref]