From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756147AbYE0C22 (ORCPT ); Mon, 26 May 2008 22:28:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753422AbYE0C2R (ORCPT ); Mon, 26 May 2008 22:28:17 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:60717 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753288AbYE0C2Q (ORCPT ); Mon, 26 May 2008 22:28:16 -0400 Date: Mon, 26 May 2008 19:28:12 -0700 (PDT) Message-Id: <20080526.192812.184590464.davem@davemloft.net> To: benh@kernel.crashing.org Cc: linux-arch@vger.kernel.org, scottwood@freescale.com, linuxppc-dev@ozlabs.org, alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, tpiepho@freescale.com Subject: Re: MMIO and gcc re-ordering issue From: David Miller In-Reply-To: <1211854540.3286.42.camel@pasglop> References: <1211852026.3286.36.camel@pasglop> <20080526.184047.88207142.davem@davemloft.net> <1211854540.3286.42.camel@pasglop> X-Mailer: Mew version 5.2 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Benjamin Herrenschmidt Date: Tue, 27 May 2008 12:15:40 +1000 > Some of them. USB comes to mind. I'd be happy to make it "the rule" and > document that MMIO vs. coherent access aren't implicitely ordered. I > would still keep them ordered on powerpc for a little while tho until > I'm happy enough with driver auditing. > > But heh, it's you who was telling me that it would be a bad engineering > decision and we had to make everybody look like x86 & fully ordered :-) > I decided to agree back then and stuck all those nasty heavy barriers > in the powerpc variants of readl/writel/... I still believe this. It's just another complicated thing for driver authors to get wrong. The other side of the coin is of course the cost. The only thing I am absolutely sure of is that we should make a decision fast, document it, and just stick to it.