linux-kernel - Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

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Message-Id: <E1J92JB-00013N-P3@be1.7eggert.dyndns.org>
Date:	Sun, 30 Dec 2007 18:50:45 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Ingo Molnar <mingo@...e.hu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rene Herman <rene.herman@...access.nl>, dpreed@...d.com,
	Islam Amer <pharon@...il.com>, hpa@...or.com,
	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

Ingo Molnar <mingo@...e.hu> wrote:

> do you have any memories about the outb_p() use of misc_32.c:
> 
>         pos = (x + cols * y) * 2;       /* Update cursor position */
>         outb_p(14, vidport);
>         outb_p(0xff & (pos >> 9), vidport+1);
>         outb_p(15, vidport);
>         outb_p(0xff & (pos >> 1), vidport+1);
> 
> was this ever needed? This is so early in the bootup that can we cannot
> do any sensible delay. Perhaps we could try a natural delay sequence via
> inb from 0x3cc:
> 
>         outb(14, vidport);
>          inb(0x3cc); /* delay */
>         outb(0xff & (pos >> 9), vidport+1);

I've never seen code which would do that, and it was not suggested by any
tutorial I ever saw. I'd expect any machine to break on all kinds of software
if it required this. The only thing I remember being warned about is writing
the index and the data register at the same time using outw, because that
would write both registers at the same time on 16-bit-cards.


BTW: The error function in linux-2.6.23/arch/i386/boot/compressed/misc.c
uses while(1) without cpu_relax() in order to halt the machine. Is this fixed?
Should it be fixed?

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