Re: How does ioremap() get non-cached mappings

From: Nagendra Singh Tomar
Date: Fri Apr 16 2004 - 00:41:54 EST

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

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)

> --
> Brian Gerst


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