Merge changes I1a57de22,If97ea5fd into integration

* changes:
  feat(locks): make spin_trylock with exclusives spin until it knows the state of the lock
  fix(locks): restore spin_trylock's ability to acquire a lock

2 files changed, 28 insertions, 15 deletions

diff --git a/include/lib/spinlock.h b/include/lib/spinlock.h
index 56d9b51a8..11826247e 100644
--- a/include/lib/spinlock.h
+++ b/include/lib/spinlock.h
@@ -26,6 +26,7 @@ void spin_unlock(spinlock_t *lock);
 void bit_lock(bitlock_t *lock, uint8_t mask);
 void bit_unlock(bitlock_t *lock, uint8_t mask);
 
+/* non-blocking spin_lock(). Returns whether the lock was acquired. */
 bool spin_trylock(spinlock_t *lock);
 
 #else
diff --git a/lib/locks/exclusive/aarch64/spinlock.c b/lib/locks/exclusive/aarch64/spinlock.c
index 20eec53f3..d568b57a4 100644
--- a/lib/locks/exclusive/aarch64/spinlock.c
+++ b/lib/locks/exclusive/aarch64/spinlock.c
@@ -94,21 +94,33 @@ static bool spin_trylock_atomic(volatile uint32_t *dst)
 static bool spin_trylock_excl(volatile uint32_t *dst)
 {
 	uint32_t src = 1;
-	uint32_t tmp;
-	bool out;
-
-	__asm__ volatile (
-	"ldaxr	%w[tmp], [%[dst]]\n"
-	"cbnz	%w[tmp], 1f\n"
-	"stxr	%w[tmp], %w[src], [%[dst]]\n"
-	"cbnz	%w[tmp], 1f\n"
-	"mov	%w[out], #1\n"
-	"1:\n" /* fail */
-	"mov	%w[out], #0\n"
-	: "+m" (*dst), [tmp] "=&r" (tmp), [out] "=r" (out)
-	:  [src] "r" (src), [dst] "r" (dst));
-
-	return out;
+	uint32_t ret;
+
+	/*
+	 * Loop until we either get the lock or are certain that we don't have
+	 * it. The exclusive store can fail due to racing and not because we
+	 * don't hold the lock.
+	 */
+	while (1) {
+		__asm__ volatile (
+		"ldaxr	%w[ret], [%[dst]]\n"
+		: [ret] "=r" (ret)
+		: "m" (*dst), [dst] "r" (dst));
+
+		/* 1 means lock is held */
+		if (ret != 0) {
+			return false;
+		}
+
+		__asm__ volatile (
+		"stxr	%w[ret], %w[src], [%[dst]]\n"
+		: "+m" (*dst), [ret] "=r" (ret)
+		: [src] "r" (src), [dst] "r" (dst));
+
+		if (ret == 0) {
+			return true;
+		}
+	}
 }
 
 /*