CONFIG_HIGHMEM on PPC

[Roman Zippel]

Hi,

On Thu, 25 Jan 2001, Dan Malek wrote:

> On the
> embedded processors, all I/O is mapped through page tables, which
> usually don't have 1:1 mapping.  The existing virt_to_phys and such
> with just the arithmetic adjustment don't work on those.

And it doesn't really have to. virt_to_bus() might be a better place for
this. virt_to_phys() is at least on ia32 a quite speed sensitive function,
that only needs to work on normal low memory.

> Some
> systems have big holes in the physical space, including physical
> addresses that map "under" the fixed kernel virtual addresses.

With holes do you mean several memory chunks? These should be handled with
memory zones.

> I don't know what you mean by more "page oriented" as that is the
> way it works now.  We just use BATs in some cases for efficiency, but
> you don't have to.

I mean drivers get a pointer to a "struct page", what they can use to
get a virtual or physical address.

bye, Roman


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