From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753787AbXLGHfV (ORCPT ); Fri, 7 Dec 2007 02:35:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751601AbXLGHfI (ORCPT ); Fri, 7 Dec 2007 02:35:08 -0500 Received: from smtpq1.tilbu1.nb.home.nl ([213.51.146.200]:37802 "EHLO smtpq1.tilbu1.nb.home.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751518AbXLGHfG (ORCPT ); Fri, 7 Dec 2007 02:35:06 -0500 Message-ID: <4758F76C.1090207@keyaccess.nl> Date: Fri, 07 Dec 2007 08:34:04 +0100 From: Rene Herman User-Agent: Thunderbird 2.0.0.9 (X11/20071031) MIME-Version: 1.0 To: "David P. Reed" CC: Robert Hancock , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops References: <4758927F.50500@shaw.ca> <4758D584.90105@keyaccess.nl> <4758E014.7040108@reed.com> <4758F373.6020901@keyaccess.nl> In-Reply-To: <4758F373.6020901@keyaccess.nl> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -1.0 (-) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07-12-07 08:17, Rene Herman wrote: > On 07-12-07 06:54, David P. Reed wrote: > >> Pardon my ignorance, but is port 0xed really safe to push an out cycle >> at across the entire x86_64 family? > > Please do not top-post. Who knows, probably not. You just experienced > that 0x80 is apparently not safe for you and that one's the conventional > choice so it's likely that someone somewhere will have problems with > 0xed as well. > > That's why I adviced you'd test and see what blows up and suggested that > in the absence of better fixes a 0x80/0xed port choice might be able to > hang off machine types as retrievable from DMI or something. > > The better fix would probably be to simply udelay(1) but you need > calibrated timers before you can do that and some googling leads me to > believe that's why it's not today. There's also a possible issue in that > an I/O access might serve as a method of flushing forwarding buffers on > a PCI bridge but I have no idea if that's a real issue (and if it is, an > inb() should suffice as well). > >> How long must real _p pauses be in reality? > > 8 ISA bus cycles is the intended delay it seems which at a typical ISA > bus speed of 8 MHz amounts to 1 us. > >> (and who cares about what the code calls "really slow i/o"). > > Paranoid programmers and those that need to delay for 4 us. > >> Why are we waiting at all? I read the comments in io_64.h, and am a >> bit mystified. Does Windoze or DOS do this magical mystery wait? > > The CMOS example at hand is the standard example. It's accessed through > an index/data register pair. You need to be sure that the RTC has > switched the correct internal register to the data register before you > poke at it or you may read/write the wrong one. > > Now, as said, I can't say I've ever in fact caught _any_ piece of > hardware with its pants down like that and needing this for actual > RTC/CMOS could as far as I'm aware be more of a left-over from The Olden > Days with a bus more or less directly tied to the 8086 than sensible for > anything on which Linux could run. Hard to test though and certainly for > generic outb_p use. > > Yes, DOS or at least many programs that ran under it did very similar > things but DOS ofcourse originated on those first PCs. > >> Anyway, the virtualization hooks in 32-bit x86 almost make it possible >> to isolate this simply - maybe - after the merge of 32/64 being >> contemplated. >> >> And anyone who knows what the chipset might be doing with the 80 port >> rather than POST codes, perhaps could contribute. Any nvidia folks >> who know what's happening under NDA? Any Phoenix BIOS types? > > It's fairly surprising that 0x80 is given you trouble. It's a very well > known legacy port. Even though it may not be all that sensible a thing > today I'd say that if your machine put anything other than an actual > integrated POST monitor on port 0x80 it in fact fucked up. This is a good thread to read: http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-09/5700.html maybe you have some LPC device that gets confused by aborts on the bus as well. Rene.