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: <4761E169.4020407@reed.com>
Date:	Thu, 13 Dec 2007 20:50:33 -0500
From:	"David P. Reed" <dpreed@...d.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	David Newall <david@...idnewall.com>,
	Rene Herman <rene.herman@...access.nl>,
	Paul Rolland <rol@...917.net>,
	"H. Peter Anvin" <hpa@...or.com>, Krzysztof Halasa <khc@...waw.pl>,
	Pavel Machek <pavel@....cz>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, rol@...be.net
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

Simulating 1 microsecond delays (assuming LPC meets that goal for 0x80) 
is "absolutely correct" for devices provided on PCI-X running on 3 GHz 
or greater machines?

Well, you are entitled to your opinion.   Seems likely that reading the 
timing specs of such a chipset might be correct, and delaying for a time 
proportional to CPU speed, rather than assuming running 3000 3GHz clock 
cycles is needed on a very fast emulation of an old device that probably 
runs at the fastest bus speed provided in the chipset.

Every device has different timing constraints.  In the real world that I 
live in.

Alan Cox wrote:
> On Thu, 13 Dec 2007 08:13:29 -0500
> "David P. Reed" <dpreed@...d.com> wrote:
>
>   
>> Perhaps what was meant is that ISA-tuned timings make little sense on 
>> devices that are part of the chipset or on the PCI or PCI-X buses?
>>     
>
> No.
>
> ISA as LPC bus is alive and well inside and outside chipsets. Welcome to
> planet earth and the reality of 'its cheaper to reuse cells than design a
> new one'. For the chipset logic like DMA controllers the _p is absolutely
> correct.
>
> Alan
>
>   
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