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SubjectRe: virt_to_bus and >1G of memory (was MAX_DMA_ADDRESS ...)
Date
In article <199811111858.TAA03864@gloin.fi.muni.cz>,
Jan Kasprzak <kas@informatics.muni.cz> wrote:
> Can anybody explain this to me? Is (x)-PAGE_OFFSET at any chance
>slower or less efficient than (x)&~PAGE_OFFSET?

No.

But the one using logical operations is safer in the presense of old
drivers that don't do the right thing. There are some historical
drivers that may mix physical and virtual addresses, and just masking
off (or turning on) the high bits makes them work even though they
shouldn't.

For 2.3.x we definitely want to use the +-PAGE_OFFSET version.

Linus

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