Fix the CAS spinlock implementation

[project/bcm63xx/atf.git] / lib / locks / exclusive / aarch64 / spinlock.S

diff --git a/lib/locks/exclusive/aarch64/spinlock.S b/lib/locks/exclusive/aarch64/spinlock.S
index d0569f1cdc95ff515dcfb5a872f324ab4f83f4b2..e941b8a3458169d18e0fbd24f46467a070ece2b9 100644 (file)
--- a/lib/locks/exclusive/aarch64/spinlock.S
+++ b/lib/locks/exclusive/aarch64/spinlock.S
@@ -9,56 +9,38 @@
        .globl  spin_lock
        .globl  spin_unlock
 
-#if ARM_ARCH_AT_LEAST(8, 1)
+#if USE_SPINLOCK_CAS
+#if !ARM_ARCH_AT_LEAST(8, 1)
+#error USE_SPINLOCK_CAS option requires at least an ARMv8.1 platform
+#endif
 
 /*
  * When compiled for ARMv8.1 or later, choose spin locks based on Compare and
  * Swap instruction.
  */
-# define USE_CAS       1
-
-/*
- * Lock contenders using CAS, upon failing to acquire the lock, wait with the
- * monitor in open state. Therefore, a normal store upon unlocking won't
- * generate an SEV. Use explicit SEV instruction with CAS unlock.
- */
-# define COND_SEV()    sev
-
-#else
-
-# define USE_CAS       0
-
-/*
- * Lock contenders using exclusive pairs, upon failing to acquire the lock, wait
- * with the monitor in exclusive state. A normal store upon unlocking will
- * implicitly generate an envent; so, no explicit SEV with unlock is required.
- */
-# define COND_SEV()
-
-#endif
-
-#if USE_CAS
 
 /*
  * Acquire lock using Compare and Swap instruction.
  *
- * Compare for 0 with acquire semantics, and swap 1. Wait until CAS returns
- * 0.
+ * Compare for 0 with acquire semantics, and swap 1. If failed to acquire, use
+ * load exclusive semantics to monitor the address and enter WFE.
  *
  * void spin_lock(spinlock_t *lock);
  */
 func spin_lock
        mov     w2, #1
-       sevl
-1:
+1:     mov     w1, wzr
+2:     casa    w1, w2, [x0]
+       cbz     w1, 3f
+       ldxr    w1, [x0]
+       cbz     w1, 2b
        wfe
-       mov     w1, wzr
-       casa    w1, w2, [x0]
-       cbnz    w1, 1b
+       b       1b
+3:
        ret
 endfunc spin_lock
 
-#else /* !USE_CAS */
+#else /* !USE_SPINLOCK_CAS */
 
 /*
  * Acquire lock using load-/store-exclusive instruction pair.
@@ -76,17 +58,18 @@ l2: ldaxr   w1, [x0]
        ret
 endfunc spin_lock
 
-#endif /* USE_CAS */
+#endif /* USE_SPINLOCK_CAS */
 
 /*
  * Release lock previously acquired by spin_lock.
  *
- * Unconditionally write 0, and conditionally generate an event.
+ * Use store-release to unconditionally clear the spinlock variable.
+ * Store operation generates an event to all cores waiting in WFE
+ * when address is monitored by the global monitor.
  *
  * void spin_unlock(spinlock_t *lock);
  */
 func spin_unlock
        stlr    wzr, [x0]
-       COND_SEV()
        ret
 endfunc spin_unlock