linux-kernel - Re: [PATCH] Clarify pci_iomap() usage for MMIO-only devices

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Message-Id: <1190154117.6403.127.camel@localhost.localdomain>
Date:	Wed, 19 Sep 2007 08:21:57 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH] Clarify pci_iomap() usage for MMIO-only devices

On Tue, 2007-09-18 at 13:30 -0700, Linus Torvalds wrote:
> Quite frankly, if performance is a _real_ reason to avoid 
> ioread*/iowrite*, I'll happily accept read*/write*, but it would be
> needed 
> to be backed up by real numbers. Can you even measure it?
> 

Also, I've been told that modern x86 chipsets have the ability to remap
IO space in the CPU physical address space. Is that true ? That would
allow even x86 to get rid of the condition and just use some magic
offset at map time.

Ben.


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