From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933759AbYETWxo (ORCPT ); Tue, 20 May 2008 18:53:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756997AbYETWxc (ORCPT ); Tue, 20 May 2008 18:53:32 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:42043 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753656AbYETWxb (ORCPT ); Tue, 20 May 2008 18:53:31 -0400 Date: Tue, 20 May 2008 15:53:26 -0700 (PDT) Message-Id: <20080520.155326.195407196.davem@davemloft.net> To: scottwood@freescale.com Cc: alan@lxorguk.ukuu.org.uk, tpiepho@freescale.com, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code From: David Miller In-Reply-To: <4833542E.3040608@freescale.com> References: <4833524C.3040207@freescale.com> <20080520.153947.84346222.davem@davemloft.net> <4833542E.3040608@freescale.com> 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: Scott Wood Date: Tue, 20 May 2008 17:43:58 -0500 > David Miller wrote: > > The __volatile__ in the asm construct disallows movement of the > > inline asm relative to statements surrounding it. > > > > The only reason barrier() in kernel.h needs a memory clobber is > > because of a bug in ancient versions of gcc. In fact, I think > > that memory clobber might even be removable. > > Current versions of GCC seem quite happy to move non-asm memory accesses > around a volatile asm without a memory clobber; see the test Trent posted. Indeed, and even the GCC manual is clear about this.