From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-4.7 required=5.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,T_DKIM_INVALID, T_RP_MATCHES_RCVD autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id D02E37DD32 for ; Wed, 28 Mar 2018 18:03:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752899AbeC1SDk (ORCPT ); Wed, 28 Mar 2018 14:03:40 -0400 Received: from merlin.infradead.org ([205.233.59.134]:57458 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751166AbeC1SDh (ORCPT ); Wed, 28 Mar 2018 14:03:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=8ral5wkuQs6TLHgSTW0awnWovHTYbuoT/4Dku0SV9q8=; b=jVGc49FGiZ8m2C0CB0V4cPnKn c6MHznqOhei83RGyHE097sCyo+dXjE/5TUa73hzPznNjRRVbl0+O/hnVjQSj2K++duCSCQLrYRWHA Pf95h+Jaui/45k6dirD5f8u/HXRi7ttTvitZoRtdpyqEjpHM5XCnQqmFFPh79B98ORTADcAwXf8aC SsSRvAHXkEc4qP8QhikoTgZhA+iwcC5Lfih1feN+xggA7dmPu9hB8p1mxyyq3tGlEgfNf9we3EXII 7ot1oACy8vaVA0eqbLoE2nVIVS0T9doy//xDF/il/h1AKNEoOvZjlqsvv5G9+dtMYg03CWx0MJgOm SkvShWlRQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1f1FPq-0003kl-Mo; Wed, 28 Mar 2018 18:03:18 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7C7AD202A4A09; Wed, 28 Mar 2018 20:03:16 +0200 (CEST) Date: Wed, 28 Mar 2018 20:03:16 +0200 From: Peter Zijlstra To: Tony Luck Cc: Sinan Kaya , Paul McKenney , Will Deacon , "linux-kernel@vger.kernel.org" , linux-doc@vger.kernel.org, Benjamin Herrenschmidt , Arnd Bergmann , Jason Gunthorpe , Ingo Molnar , Jonathan Corbet , "linux-ia64@vger.kernel.org" Subject: Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example Message-ID: <20180328180316.GN4082@hirez.programming.kicks-ass.net> References: <1522156287-15169-1-git-send-email-will.deacon@arm.com> <20180327150252.GN3675@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.3 (2018-01-21) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Mar 28, 2018 at 10:57:11AM -0700, Tony Luck wrote: > On Wed, Mar 28, 2018 at 6:02 AM, Sinan Kaya wrote: > > +linux-ia64 > > Does IA64 follow this requirement? If not, is implementation planned? > > > > "no wmb() before writel()" > > > > Linus asked us to get rid of wmb() in front of writel() for UC memory. > > Just checking that we are not breaking anything for IA64. > > We should be OK on ia64, writel() uses a cast to: > > *(volatile unsigned int __force *) > > which the compiler takes as a request to use a "st4.rel" instruction > (meaning "store with release semantics"). So the value stored will > be visible to anything that follows. Just to nitpick, regular release semantics don't guarantee anything like that, but ia64 never actually got around to implementing proper release and it's a full barrier and thus what you say is true. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html