Messages in this thread | | | Date | Fri, 16 Apr 2004 11:14:09 +0530 (IST) | From | Nagendra Singh Tomar <> | Subject | Re: How does ioremap() get non-cached mappings |
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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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