[ARM SMP] Use event instructions for spinlocks

ARMv6K CPUs have SEV (send event) and WFE (wait for event) instructions
which allow the CPU clock to be suspended until another CPU issues a
SEV, rather than spinning on the lock wasting power.  Make use of these
instructions.

Note that WFE does not wait if an event has been sent since the last WFE
cleared the event status, so although it may look racy, the instruction
implementation ensures that these are dealt with.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 24 insertions, 2 deletions

diff --git a/include/asm-arm/spinlock.h b/include/asm-arm/spinlock.h
index 6ed4f916b166..43ad4e55878c 100644
--- a/include/asm-arm/spinlock.h
+++ b/include/asm-arm/spinlock.h
@@ -30,6 +30,9 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
         __asm__ __volatile__(
 "1:     ldrex   %0, [%1]\n"
 "       teq     %0, #0\n"
+#ifdef CONFIG_CPU_32v6K
+"       wfene\n"
+#endif
 "       strexeq %0, %2, [%1]\n"
 "       teqeq   %0, #0\n"
 "       bne     1b"
@@ -65,7 +68,11 @@ static inline void __raw_spin_unlock(raw_spinlock_t *lock)
         smp_mb();
 
         __asm__ __volatile__(
-"       str     %1, [%0]"
+"       str     %1, [%0]\n"
+#ifdef CONFIG_CPU_32v6K
+"       mcr     p15, 0, %1, c7, c10, 4\n" /* DSB */
+"       sev"
+#endif
         :
         : "r" (&lock->lock), "r" (0)
         : "cc");
@@ -87,6 +94,9 @@ static inline void __raw_write_lock(raw_rwlock_t *rw)
         __asm__ __volatile__(
 "1:     ldrex   %0, [%1]\n"
 "       teq     %0, #0\n"
+#ifdef CONFIG_CPU_32v6K
+"       wfene\n"
+#endif
 "       strexeq %0, %2, [%1]\n"
 "       teq     %0, #0\n"
 "       bne     1b"
@@ -122,7 +132,11 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw)
         smp_mb();
 
         __asm__ __volatile__(
-        "str    %1, [%0]"
+        "str    %1, [%0]\n"
+#ifdef CONFIG_CPU_32v6K
+"       mcr     p15, 0, %1, c7, c10, 4\n" /* DSB */
+"       sev\n"
+#endif
         :
         : "r" (&rw->lock), "r" (0)
         : "cc");
@@ -148,6 +162,9 @@ static inline void __raw_read_lock(raw_rwlock_t *rw)
 "1:     ldrex   %0, [%2]\n"
 "       adds    %0, %0, #1\n"
 "       strexpl %1, %0, [%2]\n"
+#ifdef CONFIG_CPU_32v6K
+"       wfemi\n"
+#endif
 "       rsbpls  %0, %1, #0\n"
 "       bmi     1b"
         : "=&r" (tmp), "=&r" (tmp2)
@@ -169,6 +186,11 @@ static inline void __raw_read_unlock(raw_rwlock_t *rw)
 "       strex   %1, %0, [%2]\n"
 "       teq     %1, #0\n"
 "       bne     1b"
+#ifdef CONFIG_CPU_32v6K
+"\n     cmp     %0, #0\n"
+"       mcreq   p15, 0, %0, c7, c10, 4\n"
+"       seveq"
+#endif
         : "=&r" (tmp), "=&r" (tmp2)
         : "r" (&rw->lock)
         : "cc");