Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755242AbXLaP3v (ORCPT ); Mon, 31 Dec 2007 10:29:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751216AbXLaP3n (ORCPT ); Mon, 31 Dec 2007 10:29:43 -0500 Received: from 2-1-3-15a.ens.sth.bostream.se ([82.182.31.214]:43828 "EHLO zoo.weinigel.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905AbXLaP3m (ORCPT ); Mon, 31 Dec 2007 10:29:42 -0500 Date: Mon, 31 Dec 2007 16:29:39 +0100 From: Christer Weinigel To: Alan Cox Cc: Linus Torvalds , Rene Herman , Ingo Molnar , dpreed@reed.com, Islam Amer , hpa@zytor.com, Pavel Machek , Ingo Molnar , Andi Kleen , Thomas Gleixner , Linux Kernel Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override Message-ID: <20071231162939.2736562b@zoo.weinigel.se> In-Reply-To: <20071230211329.39ae77c2@the-village.bc.nu> References: <477711DC.5030800@keyaccess.nl> <20071230144700.78f4605c@the-village.bc.nu> <20071230152835.GX16946@elte.hu> <4777BDA5.4050203@keyaccess.nl> <20071230211329.39ae77c2@the-village.bc.nu> X-Mailer: Claws Mail 3.0.2 (GTK+ 2.12.1; x86_64-redhat-linux-gnu) 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 Content-Length: 1738 Lines: 40 On Sun, 30 Dec 2007 21:13:29 +0000 Alan Cox wrote: > > But that does't mean that other ports won't have the same timings. > > Also, it doesn't mean that we really need to have exactly *those* > > timings. > > For ISA bus you want "at least" those timings. That is an easy case > anyway - ISA bus boxes, old processors and generally no TSC so we can > fall back to 0x80 - we know from 15 years experience the problem only > occurs with recent non ISA systems that have borked firmware. > > Lots of ISA hardware does really need the delays and most of it will > be on old processors as well naturally enough. If I recall correctly, the MediaGX/Geode processor does need _p for the PIT accesses, and that CPU family does have a TSC (even though the TSC stops at times so is hard to use). I also seem to remember that the breakage did not happen very often, but running a system without _p overnight usually showed one hiccup where a read from the counter got corrupted. So unless I'm wrong (which I very well could be, it's been a couple of years since I was debugging the PIT code on a misbehaving Geode SC1200 based system) there is at least one fairly modern CPU, which is used in lots of embedded systems, and in active use, which does need the _p. Just a data point... It's not only ancient systems that need _p. /Christer -- "Just how much can I get away with and still go to heaven?" Christer Weinigel http://www.weinigel.se -- 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/