Re: making changes to agp code?

["Jan Beulich" <jbeulich@novell.com>]

>>> "Langsdorf, Mark" <mark.langsdorf@amd.com> 26.03.07 22:03 >>>
>As part of my endless quest to enable GART/IOMMU, I
>realized I need to make a slight change to a static
>function inside of agp-amd64.c.  Currently Xen doesn't
>have -xen variants of the AGP code.  Is there a 
>better way to handle this than sucking in the entire
>AGP tree into xen-sparse?
>
>As far what I need to change:
>   pci-gart calls agp_amd64_init() to determine if
>the aperture is provided by the BIOS, or if one 
>needs to be allocated.  agp_amd64_init() calls
>agp_amd64_probe() which calls another function
>and so forth, and eventually aperture_valid()
>calls 
>PageReserved(pfn_to_page(aperture >> PAGE_SHIFT)).
>The page isn't actually reserved, but dom0 thinks
>it is, and the operation fails.  I would like to
>do something more intelligent.

On a second look I believe the implementation is broken even on native,
as long as !CONFIG_FLATMEM, since there's an assumption that an
invalid PFN cannot be followed by a valid one. For that reason, I think
the code needs to be changed to call e820_any_mapped() (just like
aperture.c does). I have a tentative patch to do that, but don't have
a working box with an 8151.

Jan