From 3e2e0d2c222bdf5bafd722dec1618fa6073ef372 Mon Sep 17 00:00:00 2001 From: Chris Metcalf Date: Tue, 9 Apr 2013 12:33:07 -0400 Subject: [PATCH] tile: comment assumption about __insn_mtspr for 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 [ This came about from me wondering about the synchronization rules of __insn_mtspr() - Linus ] Signed-off-by: Linus Torvalds --- arch/tile/include/asm/irqflags.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/tile/include/asm/irqflags.h b/arch/tile/include/asm/irqflags.h index 241c0bb60b12..c96f9bbb760d 100644 --- a/arch/tile/include/asm/irqflags.h +++ b/arch/tile/include/asm/irqflags.h @@ -40,7 +40,15 @@ #include #include -/* 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 -- 2.20.1