From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751583AbaEVRQm (ORCPT ); Thu, 22 May 2014 13:16:42 -0400 Received: from terminus.zytor.com ([198.137.202.10]:54884 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751145AbaEVRQl (ORCPT ); Thu, 22 May 2014 13:16:41 -0400 Message-ID: <537E30AF.4070501@zytor.com> Date: Thu, 22 May 2014 10:15:27 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Will Deacon , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org CC: arnd@arndb.de, monstr@monstr.eu, dhowells@redhat.com, broonie@linaro.org, benh@kernel.crashing.org, peterz@infradead.org, paulmck@linux.vnet.ibm.com, Thomas Gleixner , Ingo Molnar Subject: Re: [PATCH v2 16/18] x86: io: implement dummy relaxed accessor macros for writes References: <1400777250-17335-1-git-send-email-will.deacon@arm.com> <1400777250-17335-17-git-send-email-will.deacon@arm.com> In-Reply-To: <1400777250-17335-17-git-send-email-will.deacon@arm.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/22/2014 09:47 AM, Will Deacon wrote: > write{b,w,l,q}_relaxed are implemented by some architectures in order to > permit memory-mapped I/O accesses with weaker barrier semantics than the > non-relaxed variants. > > This patch adds dummy macros for the read and write accessors to x86, > which simply expand to the non-relaxed variants. Note that this > strengthens the relaxed read accessors, since they are now ordered with > respect to each other by way of a compiler barrier. OK, do we want/need that compiler barrier? And you say "strengthens" - strengthens with respect to what if we didn't have them before? -hpa