On Sat, Aug 1, 2015 at 9:33 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> Well, it doesn't really make sense to write-combine IO memory, does it?
Quite the reverse.
It makes no sense to write-combine normal memory (RAM), because caches
work and sane memory is always cache-coherent. So marking regular
memory write-combining is a sign of crap hardware (which admittedly
exists all too much, but hopefully goes away).
In contrast, marking MMIO memory write-combining is not a sign of crap
hardware - it's just a sign of things like frame buffers on the card
etc. Which very much wants write combining. So WC for MMIO at least
makes sense.
Yes, yes, I realize that "crap hardware" may actually be the more
common case, but still..
Linus
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>