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>

1 files changed, 107 insertions, 0 deletions

diff --git a/arch/sh/include/asm/mutex-llsc.h b/arch/sh/include/asm/mutex-llsc.h
new file mode 100644
index 000000000000..7c75af5e734b
--- /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 */