Re: pgd/pmd/pte and x86 kernel virtual addresses

[Timur Tabi <ttabi@interactivesi.com>]

** Reply to message from "Benjamin C.R. LaHaise" <blah@kvack.org> on Fri, 25
Aug 2000 12:45:18 -0400 (EDT)


> > What I'm trying to do is allocate some memory via get_free_pages, and then mark
> > that memory as uncacheable.
> 
> ioremap_nocache should be able to do what you want.

Well, that's what I tried to explain in my previous email which people seem to
be ignoring.

I tried ioremap_nocache, and it doesn't appear to be working.  There are a
number of problems:

1) I'm trying to mark regular RAM as uncacheable, and ioremap_nocache()
requires me to munge the PG_Reservered bit for each page before I can do that. 
Ugly.

2) ioremap_nocache() allocates virtual RAM.  I already have a virtual address,
I don't need another one.

3) The unmap function for ioremap_nocache() is a no-op.  So after I remap and
mark the page as uncacheable, there's no way to restore it after I'm done!

4) Even with all this, it appears that the function isn't working.  I've
attached a logical analyzer to the memory bus, and writes are not being sent
out, leading me to believe the memory is still being cached.



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

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