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authorIngo Molnar <mingo@elte.hu>2008-04-27 23:21:03 +0200
committerIngo Molnar <mingo@elte.hu>2008-04-30 23:15:34 +0200
commited5e233284bc4aff965df7351da8426aa188c8f9 (patch)
treeeee6c7911672b3af57ab3f64b1e2adc4a78ff64c /arch/x86/kernel
parentfc3fbc45098e5aff59f06962dee79aba2e11430d (diff)
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>
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