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Commit 3e2e0d2c authored by Chris Metcalf's avatar Chris Metcalf Committed by Linus Torvalds
Browse files

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: default avatarChris Metcalf <cmetcalf@tilera.com>
[ This came about from me wondering about the synchronization rules of
  __insn_mtspr()   - Linus ]
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 84ee9805

arch/tile/include/asm/irqflags.h

+9 −1
Original line number Diff line number Diff line
@@ -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