Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755004AbXHUJNn (ORCPT ); Tue, 21 Aug 2007 05:13:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752633AbXHUJNd (ORCPT ); Tue, 21 Aug 2007 05:13:33 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:45051 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbXHUJNc (ORCPT ); Tue, 21 Aug 2007 05:13:32 -0400 Date: Tue, 21 Aug 2007 08:08:37 +0100 From: Russell King To: "Paul E. McKenney" Cc: Segher Boessenkool , Christoph Lameter , Paul Mackerras , heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, ak@suse.de, netdev@vger.kernel.org, cfriesen@nortel.com, akpm@linux-foundation.org, rpjday@mindspring.com, Nick Piggin , linux-arch@vger.kernel.org, jesper.juhl@gmail.com, satyam@infradead.org, zlynx@acm.org, schwidefsky@de.ibm.com, Chris Snook , Herbert Xu , davem@davemloft.net, Linus Torvalds , wensong@linux-vs.org, wjiang@resilience.com Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Message-ID: <20070821070837.GB32036@flint.arm.linux.org.uk> Mail-Followup-To: "Paul E. McKenney" , Segher Boessenkool , Christoph Lameter , Paul Mackerras , heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, ak@suse.de, netdev@vger.kernel.org, cfriesen@nortel.com, akpm@linux-foundation.org, rpjday@mindspring.com, Nick Piggin , linux-arch@vger.kernel.org, jesper.juhl@gmail.com, satyam@infradead.org, zlynx@acm.org, schwidefsky@de.ibm.com, Chris Snook , Herbert Xu , davem@davemloft.net, Linus Torvalds , wensong@linux-vs.org, wjiang@resilience.com References: <20070817235912.GA24314@linux.vnet.ibm.com> <20070818000913.GA25585@gondor.apana.org.au> <20070818010818.GQ8464@linux.vnet.ibm.com> <46C997B1.1010800@redhat.com> <417ebba299a7ad3c4b7a31c4f860a814@kernel.crashing.org> <20070820224859.GA16162@flint.arm.linux.org.uk> <2bdb04581125f22122f1d230e991ea92@kernel.crashing.org> <20070821000518.GC7292@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070821000518.GC7292@linux.vnet.ibm.com> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1216 Lines: 29 On Mon, Aug 20, 2007 at 05:05:18PM -0700, Paul E. McKenney wrote: > On Tue, Aug 21, 2007 at 01:02:01AM +0200, Segher Boessenkool wrote: > > >>And no, RMW on MMIO isn't "problematic" at all, either. > > >> > > >>An RMW op is a read op, a modify op, and a write op, all rolled > > >>into one opcode. But three actual operations. > > > > > >Maybe for some CPUs, but not all. ARM for instance can't use the > > >load exclusive and store exclusive instructions to MMIO space. > > > > Sure, your CPU doesn't have RMW instructions -- how to emulate > > those if you don't have them is a totally different thing. > > I thought that ARM's load exclusive and store exclusive instructions > were its equivalent of LL and SC, which RISC machines typically use to > build atomic sequences of instructions -- and which normally cannot be > applied to MMIO space. Absolutely correct. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - 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/