netdev - Re: wireless vs. alignment requirements

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Message-Id: <1195938799.4149.197.camel@johannes.berg>
Date:	Sat, 24 Nov 2007 22:13:19 +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


> 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.

Ok, thanks for the clarification.

Eight bytes really sucks for wireless, many things are multiples of four
and QoS vs. non-QoS frames have a multiple of four and common hardware
only adds two padding bytes to get it aligned on four bytes so there's
no easy way to get hardware to align it properly. Hmm.

johannes

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