Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751221AbWILFuL (ORCPT ); Tue, 12 Sep 2006 01:50:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751255AbWILFuK (ORCPT ); Tue, 12 Sep 2006 01:50:10 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:61574 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S1751221AbWILFuJ (ORCPT ); Tue, 12 Sep 2006 01:50:09 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Alan Cox Cc: Benjamin Herrenschmidt , Linux Kernel list , Jesse Barnes , "David S. Miller" , Jeff Garzik , Paul Mackerras , Linus Torvalds , Andrew Morton , Segher Boessenkool Subject: Re: [RFC] MMIO accessors & barriers documentation References: <1157947414.31071.386.camel@localhost.localdomain> <1157965071.23085.84.camel@localhost.localdomain> <1157966269.3879.23.camel@localhost.localdomain> <1157969261.23085.108.camel@localhost.localdomain> Date: Mon, 11 Sep 2006 23:48:33 -0600 In-Reply-To: <1157969261.23085.108.camel@localhost.localdomain> (Alan Cox's message of "Mon, 11 Sep 2006 11:07:41 +0100") Message-ID: User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 947 Lines: 28 Alan Cox writes: >> > "Except where the underlying device is marked as cachable or >> > prefetchable" >> >> You aren't supposed to use MMIO accessors on cacheable memory, are you ? > > Why not. Providing it is in MMIO space, consider ROMs for example or > write path consider frame buffers. Frame buffers are rarely cachable as such, on x86 they are usually write-combining. Which means that the writes can be merged and possibly reordered while they are being written but they can't be cached. Most arches I believe have something that roughly corresponds to write combining. Ensuring we can still use this optimization to mmio space is moderately important. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/