Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758247AbXHUJGy (ORCPT ); Tue, 21 Aug 2007 05:06:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753375AbXHUJGp (ORCPT ); Tue, 21 Aug 2007 05:06:45 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:49359 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753268AbXHUJGo (ORCPT ); Tue, 21 Aug 2007 05:06:44 -0400 Date: Tue, 21 Aug 2007 08:05:55 +0100 From: Russell King To: Segher Boessenkool Cc: Christoph Lameter , Paul Mackerras , heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, "Paul E. McKenney" , 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: <20070821070555.GA32036@flint.arm.linux.org.uk> Mail-Followup-To: Segher Boessenkool , Christoph Lameter , Paul Mackerras , heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, "Paul E. McKenney" , 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: <46C516BA.60700@yahoo.com.au> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2bdb04581125f22122f1d230e991ea92@kernel.crashing.org> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 960 Lines: 24 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. Let me say it more clearly: On ARM, it is impossible to perform atomic operations on MMIO space. -- 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/