Re: pgprot_writecombine & shub 1.x

Jesse Barnes
2005-01-12T19:32:51Z

On Wednesday, January 12, 2005 10:51 am, Jim Hull wrote:
> Jesse Barnes wrote:
> > But what about places that unconditionally set the WC bit
> > regardless of what the EFI memory map says?
>
> To be blunt - those places are broken, at least from the perspective of the
> IPF (ia64 if you prefer) architecture. IPF declares that it is the
> platform which gets to decide the supported attributes for each address
> range, and provides the EFI memory map to inform the OS of this support.
>
> > pci_mmap_page_range does this for
> > example if the write_combine flag is set on the vma.
> > I'm looking for a way to abstract out
> > uses like that, so that shub 1.x systems don't set the bit.
>
> I'm not really qualified to design the right linux interfaces, but to be
> IPF compliant, you need to change all such places to first consult the EFI
> memory map. Whether you do this once at boot time, on every call, whether
> to fail an unsupported request or remap the attribute to something the
> platform can support (e.g., mapping WC to UC), is all up to you.

Thanks for clarifying, that would certainly make things easier from our
perspective. I suppose that potentially makes the pgprot_* calls a bit more
expensive, but with the benefit that they won't clash with what EFI tells the
kernel about how memory works.

Jesse