linux-kernel - Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

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Message-ID: <20071209125458.GB4381@ucw.cz>
Date:	Sun, 9 Dec 2007 12:54:58 +0000
From:	Pavel Machek <pavel@....cz>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

Hi!

> > modern CPU compared to the bus. But the delay really needs to be something
> > that is about IO port speed. Ok in theory you could try to measure
> > a outb using RDTSC and then use udelay, but first you would need
> 
> You don't need to. Port 0x80 historically is about 8uS so just udelay(8)
> and make sure the initial default delay is conservative enough before the
> CPU speed is computed.
> 
> 0x80 should be fine for anything PC compatible anyway, its specifically
> reserved as a debug port and supported for *exactly* that purpose by
> many chipsets.

Actually, I've seen few pci cards with leds on port 0x80, and I
wonder: is our outb_p really correct?

I mean, we expect 8usec delay -- historical ISA timing -- but when
_PCI_ card with leds is inserted, it is likely to be faster than old
ISA, right?
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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