From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 29 Jan 2001 09:42:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 29 Jan 2001 09:42:40 -0500 Received: from [194.213.32.137] ([194.213.32.137]:5380 "EHLO bug.ucw.cz") by vger.kernel.org with ESMTP id ; Mon, 29 Jan 2001 09:42:22 -0500 Message-ID: <20010128232943.D1300@bug.ucw.cz> Date: Sun, 28 Jan 2001 23:29:43 +0100 From: Pavel Machek To: Rogier Wolff , "H. Peter Anvin" Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: Linux Post codes during runtime, possibly OT In-Reply-To: <3A7333FF.AA813685@transmeta.com> <200101272101.WAA27234@cave.bitwizard.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.93i In-Reply-To: <200101272101.WAA27234@cave.bitwizard.nl>; from Rogier Wolff on Sat, Jan 27, 2001 at 10:01:02PM +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > > > > It output garbage to the 80h port in order to enforce I/O delays. > > > > It's one of the safe ports to issue outs to. > > > > Yes, because it is reserved for POST codes. You can get "POST > > > debugging cards" that simply have a BIN -> 7segement encoder and two 7 > > > segment displays on them. They decode 0x80. That's what it's for. > > > Again, if you want to change it, find another safe port, test the hell > > out of it, an *PUBLICIZE IT* so noone will use it in the future. > > I may have missed too much of the discussion, but I thought that the > idea was that some people noted that their POST-code-cards don't > really work all that well when Linux is running because Linux keeps on > sending garbage to port 0x80. > > You seem to state that if you want POST codes, you should find a > different port, modify the code, test the hell out of it, and then > submit the patch. > > That is NOT the right way to go about this: Port 0x80 is RESERVED for > POST usage, that's why it's always free. If people want to use it for > the original purpose then that is a pretty damn good reason to bump > the non-intended users of that port somewhere else. > > Now, we've found that small delays are reasonably well generated with > an "outb" to 0x80. So, indeed changing that to something else is going > to be tricky. > > All that I can think of right now is: > - Find a register that can be written without side effects in > "standard" hardware like a keyboard controller, or interrupt > controller. Especially good are ones that already require us to keep > a shadow value. Write the shadow variable to the register. > (Tricky: not interrupt safe!) What about just remembering shadow of 0x80 and always writing shadow to 0x80? Interrupt unsafety hopefully does not matter much.... Pavel -- I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/