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Subjectvirt_to_bus and >1G of memory (was MAX_DMA_ADDRESS ...)

In my previous mail I wrote:
: And another question related to the virt_to_bus on x86:
: This function is defined as (x) & ~PAGE_OFFSET. It works for the current
: value of the PAGE_OFFSET, but IMHO it does not work when I change the
: PAGE_OFFSET to 0x70000000, as suggested in <asm-i386/page.h> for >1GB RAM
: machines. Shouldn't the virt_to_bus be defined as (x)-PAGE_OFFSET ?
: The physical memory is mapped 1:1 from the PAGE_OFFSET virtual address, IIRC.

Can anybody explain this to me? Is (x)-PAGE_OFFSET at any chance
slower or less efficient than (x)&~PAGE_OFFSET?


\ Jan "Yenya" Kasprzak <kas at>
\\ PGP: finger kas at 0D99A7FB206605D7 8B35FCDE05B18A5E //
\\\ Czech Linux Homepage: ///
/// I think I'd rather be forced to learn perl than 68020 MMU. -Alan Cox \\\
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