virt_to_bus and >1G of memory (was MAX_DMA_ADDRESS ...)
Jan Kasprzak (kas@informatics.muni.cz)
Wed, 11 Nov 1998 19:58:36 +0100
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?
-Yenya
--
\ Jan "Yenya" Kasprzak <kas at fi.muni.cz> http://www.fi.muni.cz/~kas/
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\\\ Czech Linux Homepage: http://www.linux.cz/ ///
/// I think I'd rather be forced to learn perl than 68020 MMU. -Alan Cox \\\
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