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Message-Id: <1195893216.4149.186.camel@johannes.berg>
Date: Sat, 24 Nov 2007 09:33:36 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: dsd@...too.org, davem@...emloft.net, netdev@...r.kernel.org,
linux-wireless@...r.kernel.org
Subject: Re: wireless vs. alignment requirements
> > Now, the IP stack actually assumes that its header is four-byte aligned
> > (see comment at NET_IP_ALIGN, although it is not said explicitly that
> > the alignment requirement for an IP header is four) so that is actually
> > something for the hardware/firmware (!) to do, for example Broadcom
>
> Good point. In fact IIRC we've always had the policy that drivers
> should do their best to generate aligned packets but it is not a
> requirement since on some platforms it's more important for the DMA
> to be aligned.
We still require four-byte alignment, no?
> So it's up the platform code to fix up any exceptions should they
> show up.
>
> Daniel, what's the specific case that you had in mind with this
> patch?
Well. This goes back to a user reporting unaligned accesses on sparc64.
Davem thought this came from the ether addr comparisons but the user
later reported that the patch from davem didn't fix it, and I think
Daniel just made a sweep over all ether addr comparisons replacing them
with unaligned ones.
johannes
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