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

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Date:	Mon, 17 Dec 2007 16:02:20 -0500
From:	"David P. Reed" <dpreed@...d.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Rene Herman <rene.herman@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Paul Rolland <rol@...917.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@....cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	rol@...be.net
Subject: Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

H. Peter Anvin wrote:
> David P. Reed wrote:
>> As support: port 80 on the reporter's (my) HP dv9000z laptop clearly 
>> responds to reads differently than "unused" ports.  In particular, an 
>> inb takes 1/2 the elapsed time compared to a read to "known" unused 
>> port 0xed - 792 tsc ticks for port 80 compared to about 1450 tsc 
>> ticks for port 0xed and other unused ports (tsc at 800 MHz).
>>
>
> Any timings for port 0xf0 (write zero), out of curiosity?
>

Here's a bunch of data:

port 0xF0: cycles: out 919, in 933
port 0xed: cycles: out 2541, in 2036
port 0x70: cycles: out n/a,  in 934
port 0x80: cycles: out 1424, in 795

AMD Turion 64x2 TL-60 CPU running at 800 MHz, nVidia MCP51 chipset, 
Quanta motherboard.  Running 2.6.24-rc5 with Ingo's patch so inb_p, etc. 
use port 0xed.

Note that I can run the port 80 test once, the second time I get the 
hard freeze.  I didn't try writing to port 70 from userspace - that 
one's dangerous, but the reading of it was included for a timing typical 
of a chipset supported device.  These are all pretty consistent.

I find the "read" timing from 0x80 verrrrry interesting.  The write 
timeing is also interesting, being faster than an unused port. 

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