sh: Add SH-4A optimized fastpath mutex implementation.
Add fast mutex path implementation for the SH4A architecture
Signed-off-by: Michael Trimarchi <trimarchimichael@yahoo.it>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/include/asm/mutex-llsc.h b/arch/sh/include/asm/mutex-llsc.h
new file mode 100644
index 0000000..7c75af5
--- /dev/null
+++ b/arch/sh/include/asm/mutex-llsc.h
@@ -0,0 +1,107 @@
+/*
+ * arch/sh/include/asm/mutex-llsc.h
+ *
+ * SH-4A optimized mutex locking primitives
+ *
+ * Please look into asm-generic/mutex-xchg.h for a formal definition.
+ */
+#ifndef __ASM_SH_MUTEX_LLSC_H
+#define __ASM_SH_MUTEX_LLSC_H
+
+/*
+ * Attempting to lock a mutex on SH4A is done like in ARMv6+ architecure.
+ * with a bastardized atomic decrement (it is not a reliable atomic decrement
+ * but it satisfies the defined semantics for our purpose, while being
+ * smaller and faster than a real atomic decrement or atomic swap.
+ * The idea is to attempt decrementing the lock value only once. If once
+ * decremented it isn't zero, or if its store-back fails due to a dispute
+ * on the exclusive store, we simply bail out immediately through the slow
+ * path where the lock will be reattempted until it succeeds.
+ */
+static inline void
+__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
+{
+ int __res;
+
+ __asm__ __volatile__ (
+ "movli.l @%1, %0 \n"
+ "dt %0 \n"
+ "movco.l %0, @%1 \n"
+ : "=&z" (__res)
+ : "r" (&(count)->counter)
+ : "t");
+
+ if (unlikely(__res != 0))
+ fail_fn(count);
+}
+
+static inline int
+__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
+{
+ int __res;
+
+ __asm__ __volatile__ (
+ "movli.l @%1, %0 \n"
+ "dt %0 \n"
+ "movco.l %0, @%1 \n"
+ : "=&z" (__res)
+ : "r" (&(count)->counter)
+ : "t");
+
+ if (unlikely(__res != 0))
+ __res = fail_fn(count);
+
+ return __res;
+}
+
+static inline void
+__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
+{
+ int __res;
+
+ __asm__ __volatile__ (
+ "1: movli.l @%1, %0 \n\t"
+ "add #1, %0 \n\t"
+ "movco.l %0, @%1 \n\t"
+ "bf 1b\n\t"
+ : "=&z" (__res)
+ : "r" (&(count)->counter)
+ : "t");
+
+ if (unlikely(__res <= 0))
+ fail_fn(count);
+}
+
+/*
+ * If the unlock was done on a contended lock, or if the unlock simply fails
+ * then the mutex remains locked.
+ */
+#define __mutex_slowpath_needs_to_unlock() 1
+
+/*
+ * For __mutex_fastpath_trylock we do an atomic decrement and check the
+ * result and put it in the __res variable.
+ */
+static inline int
+__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
+{
+ int __res, __orig;
+
+ __asm__ __volatile__ (
+ "1: movli.l @%2, %0 \n\t"
+ "dt %0 \n\t"
+ "movco.l %0,@%2 \n\t"
+ "bf 1b \n\t"
+ "cmp/eq #0,%0 \n\t"
+ "bt 2f \n\t"
+ "mov #0, %1 \n\t"
+ "bf 3f \n\t"
+ "2: mov #1, %1 \n\t"
+ "3: "
+ : "=&z" (__orig), "=&r" (__res)
+ : "r" (&count->counter)
+ : "t");
+
+ return __res;
+}
+#endif /* __ASM_SH_MUTEX_LLSC_H */
