Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753805AbXLKNua (ORCPT ); Tue, 11 Dec 2007 08:50:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751535AbXLKNuW (ORCPT ); Tue, 11 Dec 2007 08:50:22 -0500 Received: from one.firstfloor.org ([213.235.205.2]:32996 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751387AbXLKNuW (ORCPT ); Tue, 11 Dec 2007 08:50:22 -0500 Date: Tue, 11 Dec 2007 14:50:20 +0100 From: Andi Kleen To: Pavel Machek Cc: Andi Kleen , Alan Cox , David Newall , "H. Peter Anvin" , Krzysztof Halasa , Rene Herman , "David P. Reed" , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops Message-ID: <20071211135020.GB16750@one.firstfloor.org> References: <20071209165908.GA15910@one.firstfloor.org> <20071209212513.GC24284@elf.ucw.cz> <475CBDD7.5050602@keyaccess.nl> <475DE37F.20706@davidnewall.com> <475DE6F4.80702@zytor.com> <475DEB23.1000304@davidnewall.com> <20071211131413.1079be59@the-village.bc.nu> <20071211133249.GA16750@one.firstfloor.org> <20071211134725.GB17992@elf.ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071211134725.GB17992@elf.ucw.cz> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1394 Lines: 31 On Tue, Dec 11, 2007 at 02:47:25PM +0100, Pavel Machek wrote: > On Tue 2007-12-11 14:32:49, Andi Kleen wrote: > > > The LPC bus behaviour is absolutely and precisely defined. The timing of > > > the inb is defined in bus clocks which is perfect as the devices needing > > > delay are running at a fraction of busclock usually busclock/2. > > > > > > Older processors did not have a high precision timer so you couldn't > > > calibrate loop based delays for 1uS. > > > > For newer CPUs udelay() would be probably fine though. We seem > > to have several documented examples now where the bus aborts > > trigger hardware bugs, and it is always better to avoid such situations. > > > > I still think the best strategy would be to switch based on TSC > > availability. Perhaps move out*_p out of line to avoid code bloat. > > Why is TSC significant? udelay() based on bogomips seems to be good > enough...? Maybe I'm not sure how accurate it really is on non TSC system. On the other hand it is unclear that the port 80 IO is always the same time so it's probably ok to vary a bit. So most likely going to udelay() unconditionally is fine. -Andi -- 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/