Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757164AbYFCSsE (ORCPT ); Tue, 3 Jun 2008 14:48:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751311AbYFCSry (ORCPT ); Tue, 3 Jun 2008 14:47:54 -0400 Received: from az33egw02.freescale.net ([192.88.158.103]:37803 "EHLO az33egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753176AbYFCSrx (ORCPT ); Tue, 3 Jun 2008 14:47:53 -0400 Date: Tue, 3 Jun 2008 11:47:00 -0700 (PDT) From: Trent Piepho X-X-Sender: xyzzy@t2.domain.actdsltmp To: Linus Torvalds cc: Nick Piggin , Russell King , Benjamin Herrenschmidt , David Miller , linux-arch@vger.kernel.org, scottwood@freescale.com, linuxppc-dev@ozlabs.org, alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org Subject: Re: MMIO and gcc re-ordering issue In-Reply-To: Message-ID: References: <1211852026.3286.36.camel@pasglop> <20080602072403.GA20222@flint.arm.linux.org.uk> <200806031416.18195.nickpiggin@yahoo.com.au> 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 Content-Length: 1111 Lines: 25 On Tue, 3 Jun 2008, Linus Torvalds wrote: > On Tue, 3 Jun 2008, Nick Piggin wrote: >> >> Linus: on x86, memory operations to wc and wc+ memory are not ordered >> with one another, or operations to other memory types (ie. load/load >> and store/store reordering is allowed). Also, as you know, store/load >> reordering is explicitly allowed as well, which covers all memory >> types. So perhaps it is not quite true to say readl/writel is strongly >> ordered by default even on x86. You would have to put in some >> mfence instructions in them to make it so. So on x86, these could be re-ordered? writel(START_OPERATION, CONTROL_REGISTER); status = readl(STATUS_REGISTER); > Well, you have to ask for WC/WC+ anyway, so it's immaterial. A driver that > does that needs to be aware of it. IOW, it's a non-issue, imnsho. You need to ask for coherent DMA memory too. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/