x86, voyager: fix ioremap_nocache()

James Bottomley reported that the following commit:

| commit 6371b495991debfd1417b17c2bc4f7d7bae05739
| Author: Ingo Molnar <mingo@elte.hu>
| Date:   Wed Jan 30 13:33:40 2008 +0100
|
|     x86: change ioremap() to default to uncached

broke Voyager.

James says:

" it broke a class of voyager machines: those which
  rely on the quad interrupt controller (QIC).  The precis of why they
  broke is because the QIC does IPIs (or CPIs in its terminology) via
  cache line interference: you interrupt a processor by moving a
  designated memory area to write exclusive in the cache (by simply
  writing to the line) and the CPU acks the interrupt by moving it back to
  read shared (by reading from it).  That area, is, of course, mapped by
  ioremap, so reversing the ioremap semantics and adding the uncached bit
  completely breaks the QIC. "

Sorry about that!

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

0 files changed, 0 insertions, 0 deletions