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authorChris Metcalf <cmetcalf@tilera.com>2013-04-09 12:33:07 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2013-04-09 10:08:14 -0700
commit3e2e0d2c222bdf5bafd722dec1618fa6073ef372 (patch)
tree04ea03bb23d59080ce52012095591874cad6cf49 /arch/tile
parent84ee9805bc7406bee35f2d62001440c81059f073 (diff)
downloadlinux-3e2e0d2c222bdf5bafd722dec1618fa6073ef372.tar.gz
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: Chris Metcalf <cmetcalf@tilera.com> [ This came about from me wondering about the synchronization rules of __insn_mtspr() - Linus ] Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/tile')
-rw-r--r--arch/tile/include/asm/irqflags.h10
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/tile/include/asm/irqflags.h b/arch/tile/include/asm/irqflags.h
index 241c0bb60b1..c96f9bbb760 100644
--- a/arch/tile/include/asm/irqflags.h
+++ b/arch/tile/include/asm/irqflags.h
@@ -40,7 +40,15 @@
#include <asm/percpu.h>
#include <arch/spr_def.h>
-/* Set and clear kernel interrupt masks. */
+/*
+ * Set and clear kernel interrupt masks.
+ *
+ * NOTE: __insn_mtspr() is a compiler builtin marked as a memory
+ * clobber. We rely on it being equivalent to a compiler barrier in
+ * this code since arch_local_irq_save() and friends must act as
+ * compiler barriers. This compiler semantic is baked into enough
+ * places that the compiler will maintain it going forward.
+ */
#if CHIP_HAS_SPLIT_INTR_MASK()
#if INT_PERF_COUNT < 32 || INT_AUX_PERF_COUNT < 32 || INT_MEM_ERROR >= 32
# error Fix assumptions about which word various interrupts are in