From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: MMIO and gcc re-ordering issue Date: Tue, 3 Jun 2008 07:47:26 -0700 (PDT) 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 Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:42135 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753876AbYFCOr6 (ORCPT ); Tue, 3 Jun 2008 10:47:58 -0400 In-Reply-To: <200806031416.18195.nickpiggin@yahoo.com.au> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Nick Piggin Cc: Russell King , Benjamin Herrenschmidt , David Miller , linux-arch@vger.kernel.org, scottwood@freescale.com, linuxppc-dev@ozlabs.org, alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org, tpiepho@freescale.com 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