Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758043AbYFCT7R (ORCPT ); Tue, 3 Jun 2008 15:59:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754871AbYFCT7E (ORCPT ); Tue, 3 Jun 2008 15:59:04 -0400 Received: from az33egw02.freescale.net ([192.88.158.103]:63713 "EHLO az33egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754861AbYFCT7B (ORCPT ); Tue, 3 Jun 2008 15:59:01 -0400 Date: Tue, 3 Jun 2008 12:57:56 -0700 (PDT) From: Trent Piepho X-X-Sender: xyzzy@t2.domain.actdsltmp To: Matthew Wilcox cc: Linus Torvalds , 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: <20080603185541.GB3549@parisc-linux.org> Message-ID: References: <1211852026.3286.36.camel@pasglop> <20080602072403.GA20222@flint.arm.linux.org.uk> <200806031416.18195.nickpiggin@yahoo.com.au> <20080603185541.GB3549@parisc-linux.org> 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: 1254 Lines: 28 On Tue, 3 Jun 2008, Matthew Wilcox wrote: > On Tue, Jun 03, 2008 at 11:47:00AM -0700, Trent Piepho wrote: >> 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); > > You wouldn't ask for write-combining memory mapping for control or > status registers. But Nick said, "store/load reordering is explicitly allowed as well, which covers *all* memory types." -- 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/