** Reply to message from "Stephen C. Tweedie" [off-list ref] on Tue, 29 Aug
2000 00:09:35 +0100

quoted

physical pointer.  The first is the normal virtual pointer for kernel memory,
and the second is the one returned by ioremap_nocache().  I was under the
understanding that caching is enabled on physical pages only, so it shouldn't
matter which virtual address I use.  Is that correct?

No.  The no-cache bit is set in the page table entry, so depends on
the virtual address.  There is a *different* form of memory access
control which can be used to make memory non-cachable, and that is the
"mtrr" (Memory Type Range Register), which exists in different forms
on all recent Intel and AMD cpus.  Mtrrs work on physical addresses,
but that is not what ioremap_nocache() uses.

Ok, thanks!  That explains a whole lot.

Another question: is there a way I can enable Write Combining on a page,
without using MTRR's?



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Timur Tabi - ttabi@interactivesi.com
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