From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: MMIO and gcc re-ordering issue Date: Mon, 2 Jun 2008 12:36:43 +0200 Message-ID: <20080602103643.GA21285@elte.hu> References: <1211852026.3286.36.camel@pasglop> <20080526.184047.88207142.davem@davemloft.net> <1211854540.3286.42.camel@pasglop> <20080526.192812.184590464.davem@davemloft.net> <1211859542.3286.46.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx2.mail.elte.hu ([157.181.151.9]:60069 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751736AbYFBKiA (ORCPT ); Mon, 2 Jun 2008 06:38:00 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds Cc: 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 * Linus Torvalds wrote: > > Here's a UNTESTED patch for x86 that may or may not compile and > > work, and which serializes (on a compiler level) the IO accesses > > against regular memory accesses. > > Ok, so it at least boots on x86-32. Thus probably on x86-64 too (since > the code is now shared). I didn't look at whether it generates much > bigger code due to the potential extra serialization, but some of the > code generation I looked at looked fine. > > IOW, it doesn't at least create any _obviously_ worse code, and it > should be arguably safer than assuming the compiler does volatile > accesses the way we want it to. ok, to pursue this topic of making readl*/writel*() more robust i picked up your patch into -tip and created a new topic branch for it: tip/x86/mmio. The patch passed initial light testing in -tip (~30 successful random self-builds and bootups on various mixed 32-bit/64-bit boxes) but it's still v2.6.27 material IMO. Failures in this area are subtle so there's no good way to tell whether it works as intended - we need wider testing. I've also added the tip/x86/mmio topic to tip/auto-x86-next rules as well so these changes will be picked up by tomorrow's linux-next tree as well, and by the next -mm iteration. Ingo