** Reply to message from Jeff Hartmann [off-list ref] on Wed, 24 Jan
2001 13:41:41 -0700

When you mark a page UCWC, you better 
have removed all cached mappings or your asking for REAL trouble.

What exactly do you mean by "removed all cached mappings"?  Does that mean that
if one virtual address is a UCWC mapping of a physical page, then ALL virtual
addresses mapped to that page must also be UCWC?

In my driver, I use ioremap_nocache() on physical memory (real RAM) to create
an uncached "alias" (a virtual address) to a physical page of RAM.  When I
access the memory via this virtual address, the memory access is not cached.
What I reall need is to be able to also have that virtual address as Write
Combined.

Since all physical RAM is mapped as cached via the kernel (on a 1-to-1 basis),
and since there can be several other virtual addresses that point to that memory
(e.g. user virtual address), I can't see how these virtual addresses can be
removed.


-- 
Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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