* How does ioremap() get non-cached mappings
@ 2004-04-16 5:11 Nagendra Singh Tomar
2004-04-16 5:32 ` Brian Gerst
0 siblings, 1 reply; 3+ messages in thread
From: Nagendra Singh Tomar @ 2004-04-16 5:11 UTC (permalink / raw)
To: linux-kernel; +Cc: Tomar, Nagendra
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 ?
Thanx,
tomar
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* Re: How does ioremap() get non-cached mappings
2004-04-16 5:11 How does ioremap() get non-cached mappings Nagendra Singh Tomar
@ 2004-04-16 5:32 ` Brian Gerst
2004-04-16 5:44 ` Nagendra Singh Tomar
0 siblings, 1 reply; 3+ messages in thread
From: Brian Gerst @ 2004-04-16 5:32 UTC (permalink / raw)
To: Tomar, Nagendra; +Cc: linux-kernel
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()
--
Brian Gerst
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: How does ioremap() get non-cached mappings
2004-04-16 5:32 ` Brian Gerst
@ 2004-04-16 5:44 ` Nagendra Singh Tomar
0 siblings, 0 replies; 3+ messages in thread
From: Nagendra Singh Tomar @ 2004-04-16 5:44 UTC (permalink / raw)
To: Brian Gerst; +Cc: Tomar, Nagendra, linux-kernel
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
>
--
-- You have moved the mouse. Windows must be restarted for the
changes to take effect.
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2004-04-16 5:11 How does ioremap() get non-cached mappings Nagendra Singh Tomar
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