Date: Fri, 16 Apr 2004 11:14:09 +0530 (IST)
From: Nagendra Singh Tomar <nagendra_tomar@adaptec.com>
Reply-To: "Tomar, Nagendra" <nagendra_tomar@adaptec.com>
To: Brian Gerst <bgerst@didntduck.org>
cc: "Tomar, Nagendra" <nagendra_tomar@adaptec.com>,
       <linux-kernel@vger.kernel.org>
Subject: Re: How does ioremap() get non-cached mappings
In-Reply-To: <407F6FF8.1020904@quark.didntduck.org>
Message-ID: <Pine.LNX.4.44.0404161111250.17679-100000@localhost.localdomain>
Organization: Adaptec
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On Fri, 16 Apr 2004, Brian Gerst wrote:

> Nagendra Singh Tomar wrote:
> > ioremap() function in x86 arch code does not seem to be setting _PAGE_PCD 
> > bit in the PTE. How then does it give non-cached mapping to MMIO mappings 
> > for memory on some interface card. I have gone thru some old threads on 
> > this, which have concluded that it does give non-cached mappings, and 
> > moerover ioremap seems to work fine whenever I have used to map any PCI 
> > card memory,
> > Is it guaranteed thru the means of MTRR ?
> > 
> 
> ioremap_nocache()

I'm aware of ioremap_nocache(), and the fact that it explicitly sets 
_PAGE_PCD. My  question originated after reading this posting by Alan

http://www.uwsg.iu.edu/hypermail/linux/kernel/0110.0/0878.html

in which he explicitly states that ioremap() gives uncached mapping. If 
you follow the thread, there is a general consensus that ioremap and 
ioremap_nocache are functionaly the same on x86 arch (and I suppose on 
most archs)

Thanx,
tomar
> 
> --
> 				Brian Gerst
> 

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