From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934615AbYETW0r (ORCPT ); Tue, 20 May 2008 18:26:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1765127AbYETW02 (ORCPT ); Tue, 20 May 2008 18:26:28 -0400 Received: from az33egw02.freescale.net ([192.88.158.103]:40131 "EHLO az33egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933422AbYETW01 (ORCPT ); Tue, 20 May 2008 18:26:27 -0400 Date: Tue, 20 May 2008 15:21:13 -0700 (PDT) From: Trent Piepho X-X-Sender: xyzzy@t2.domain.actdsltmp To: Benjamin Herrenschmidt cc: Scott Wood , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code In-Reply-To: <1211320938.8297.179.camel@pasglop> Message-ID: References: <1211316025-29069-1-git-send-email-tpiepho@freescale.com> <1211318219.8297.177.camel@pasglop> <483344C0.3020703@freescale.com> <1211320938.8297.179.camel@pasglop> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 May 2008, Benjamin Herrenschmidt wrote: > On Tue, 2008-05-20 at 16:38 -0500, Scott Wood wrote: >> It looks like we rely on -fno-strict-aliasing to prevent reordering >> ordinary memory accesses (such as to DMA descriptors) past the I/O >> access. It won't prevent reordering of memory reads around an I/O >> read, >> though, which could be a problem if the I/O read result determines >> the >> validity of the DMA buffer. IMHO, a memory clobber would be better. > > We probably want a full "memory" clobber then... As far as I could tell, no other arch has a full memory clobber. I can see the argument for changing the Linux model to be stricter and less efficient, but easier to program for. Not that I entirely agree with it. But I don't see a good reason for why powerpc should be different than everything else.