From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from terminus.zytor.com ([198.137.202.10]:50390 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757960AbXK0RRR (ORCPT ); Tue, 27 Nov 2007 12:17:17 -0500 Message-ID: <474C50D7.5010901@zytor.com> (sfid-20071127_171720_947445_2BC3AF76) Date: Tue, 27 Nov 2007 09:16:07 -0800 From: "H. Peter Anvin" MIME-Version: 1.0 To: Stephen Hemminger CC: Herbert Xu , Johannes Berg , dsd@gentoo.org, davem@davemloft.net, netdev@vger.kernel.org, linux-wireless@vger.kernel.org Subject: Re: wireless vs. alignment requirements 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> <4748855C.5090103@linux-foundation.org> In-Reply-To: <4748855C.5090103@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: Stephen Hemminger wrote: > 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. 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