From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: MMIO and gcc re-ordering issue Date: Fri, 30 May 2008 08:05:39 +1000 Message-ID: <1212098739.8888.58.camel@pasglop> References: <1211852026.3286.36.camel@pasglop> <20080526.184047.88207142.davem@davemloft.net> <1211854540.3286.42.camel@pasglop> <20080526.192812.184590464.davem@davemloft.net> <20080526204233.75b71bb8@infradead.org> <1211872130.3286.64.camel@pasglop> <1211922696.3286.82.camel@pasglop> <1212097223.8888.55.camel@pasglop> Reply-To: benh@kernel.crashing.org Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from gate.crashing.org ([63.228.1.57]:54941 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754866AbYE2WHl (ORCPT ); Thu, 29 May 2008 18:07:41 -0400 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Trent Piepho Cc: Jes Sorensen , Roland Dreier , Arjan van de Ven , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, scottwood@freescale.com, torvalds@linux-foundation.org, David Miller , alan@lxorguk.ukuu.org.uk On Thu, 2008-05-29 at 14:48 -0700, Trent Piepho wrote: > I wrote a JTAG over gpio driver for the powerpc MPC8572DS platform. With the > non-raw io accessors, the JTAG clock can run at almost ~9.5 MHz. Using raw > versions (which I had to write since powerpc doesn't have any), the clock > speed increases to about 28 MHz. So it can make a very significant different. Yes, sync's can hurt a lot. This is why I initially tried to get more relaxed semantics. We could implement something like __ variants and do something that would still have eieio's but not sync's for example (ie. MMIOs are still ordered vs. each other but not vs. coherent memory). Ben.