From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Date: Mon, 20 Aug 2007 23:48:59 +0100 Message-ID: <20070820224859.GA16162@flint.arm.linux.org.uk> References: <46C505B2.6030704@yahoo.com.au> <18117.4848.695269.72976@cargo.ozlabs.ibm.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Chris Snook , 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, Herbert Xu , davem@davemloft.net, Linus Torvalds , wensong@linux-vs.org, wjiang@resilience.com To: Segher Boessenkool Return-path: Content-Disposition: inline In-Reply-To: <417ebba299a7ad3c4b7a31c4f860a814@kernel.crashing.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Aug 21, 2007 at 12:04:17AM +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. This means placing atomic_t or bitops into MMIO space is a definite no-go on ARM. It breaks. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: