tile: comment assumption about __insn_mtspr for <asm/irqflags.h>
The arch_local_irq_save(), etc., routines are required to function as compiler barriers. They do, but it's subtle and requires knowing that the gcc builtin __insn_mtspr() is marked as a memory clobber. Provide a comment explaining the assumption. Signed-off-by: NChris Metcalf <cmetcalf@tilera.com> [ This came about from me wondering about the synchronization rules of __insn_mtspr() - Linus ] Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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