From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linux-foundation.org (smtp1.linux-foundation.org [140.211.169.13]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "smtp.linux-foundation.org", Issuer "CA Cert Signing Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id D571CDE9D1 for ; Wed, 4 Jun 2008 00:47:56 +1000 (EST) Date: Tue, 3 Jun 2008 07:47:26 -0700 (PDT) From: Linus Torvalds To: Nick Piggin Subject: Re: MMIO and gcc re-ordering issue In-Reply-To: <200806031416.18195.nickpiggin@yahoo.com.au> Message-ID: References: <1211852026.3286.36.camel@pasglop> <20080602072403.GA20222@flint.arm.linux.org.uk> <200806031416.18195.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: linux-arch@vger.kernel.org, Russell King , linux-kernel@vger.kernel.org, tpiepho@freescale.com, linuxppc-dev@ozlabs.org, scottwood@freescale.com, David Miller , alan@lxorguk.ukuu.org.uk List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 3 Jun 2008, Nick Piggin wrote: > > Linus: on x86, memory operations to wc and wc+ memory are not ordered > with one another, or operations to other memory types (ie. load/load > and store/store reordering is allowed). Also, as you know, store/load > reordering is explicitly allowed as well, which covers all memory > types. So perhaps it is not quite true to say readl/writel is strongly > ordered by default even on x86. You would have to put in some > mfence instructions in them to make it so. Well, you have to ask for WC/WC+ anyway, so it's immaterial. A driver that does that needs to be aware of it. IOW, it's a non-issue, imnsho. Linus