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

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Date:	Mon, 10 Dec 2007 17:51:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Newall <david@...idnewall.com>
CC:	Krzysztof Halasa <khc@...waw.pl>,
	Rene Herman <rene.herman@...access.nl>,
	Pavel Machek <pavel@....cz>, Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

David Newall wrote:
> 
> Exactly.  You think it's 2us, but the documentation doesn't say.  The _p 
> functions are generic inasmuch as they provide an unspecified delay.  
> Drivers which work across platforms, and which use _p, therefore have 
> different delays on different platforms.  Should the length of the delay 
> be unimportant?  I wouldn't have thought so.  If it is important, does 
> that mean that such drivers are buggy on some platforms?
> 

That the _p delay is different across platforms is actually to be 
expected, since it pretty much amounts to a platform delay.  And yes, if 
it is used as a specific walltime delay that has nothing to do with the 
bus architecture of the system then I would classify that as a driver bug.

	-hpa
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