From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: wireless vs. alignment requirements Date: Sat, 24 Nov 2007 12:11:08 -0800 Message-ID: <4748855C.5090103@linux-foundation.org> References: <1195893216.4149.186.camel@johannes.berg> <20071124133200.GA27531@gondor.apana.org.au> <1195912176.4149.194.camel@johannes.berg> <20071124141319.GA27819@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Johannes Berg , dsd-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Herbert Xu Return-path: In-Reply-To: <20071124141319.GA27819-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org> Sender: linux-wireless-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org Herbert Xu wrote: > On Sat, Nov 24, 2007 at 02:49:36PM +0100, Johannes Berg wrote: > >> 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.