sparc64: Make rwsems 64-bit.

Basically tip-off the powerpc code, use a 64-bit type and atomic64_t
interfaces for the implementation.

This gets us off of the by-hand asm code I wrote, which frankly I
think probably ruins I-cache hit rates.

The idea was the keep the call chains less deep, but anything taking
the rw-semaphores probably is also calling other stuff and therefore
already has allocated a stack-frame.  So no real stack frame savings
ever.

Ben H. has posted patches to make powerpc use 64-bit too and with some
abstractions we can probably use a shared header file somewhere.

With suggestions from Sam Ravnborg.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 103 insertions, 29 deletions

diff --git a/arch/sparc/include/asm/rwsem-const.h b/arch/sparc/include/asm/rwsem-const.h
deleted file mode 100644
index e4c61a18bb28..000000000000
--- a/arch/sparc/include/asm/rwsem-const.h
+++ /dev/null
@@ -1,12 +0,0 @@
-/* rwsem-const.h: RW semaphore counter constants.  */
-#ifndef _SPARC64_RWSEM_CONST_H
-#define _SPARC64_RWSEM_CONST_H
-
-#define RWSEM_UNLOCKED_VALUE            0x00000000
-#define RWSEM_ACTIVE_BIAS               0x00000001
-#define RWSEM_ACTIVE_MASK               0x0000ffff
-#define RWSEM_WAITING_BIAS              (-0x00010000)
-#define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
-#define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
-
-#endif /* _SPARC64_RWSEM_CONST_H */
diff --git a/arch/sparc/include/asm/rwsem.h b/arch/sparc/include/asm/rwsem.h
index 6e5621006f85..a2b4302869bc 100644
--- a/arch/sparc/include/asm/rwsem.h
+++ b/arch/sparc/include/asm/rwsem.h
@@ -15,16 +15,21 @@
 
 #include <linux/list.h>
 #include <linux/spinlock.h>
-#include <asm/rwsem-const.h>
 
 struct rwsem_waiter;
 
 struct rw_semaphore {
-        signed int count;
-        spinlock_t              wait_lock;
-        struct list_head        wait_list;
+        signed long                     count;
+#define RWSEM_UNLOCKED_VALUE            0x00000000L
+#define RWSEM_ACTIVE_BIAS               0x00000001L
+#define RWSEM_ACTIVE_MASK               0xffffffffL
+#define RWSEM_WAITING_BIAS              (-RWSEM_ACTIVE_MASK-1)
+#define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
+#define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
+        spinlock_t                      wait_lock;
+        struct list_head                wait_list;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-        struct lockdep_map      dep_map;
+        struct lockdep_map              dep_map;
 #endif
 };
 
@@ -41,6 +46,11 @@ struct rw_semaphore {
 #define DECLARE_RWSEM(name) \
         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
 
+extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
+extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
+extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
+extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
+
 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
                          struct lock_class_key *key);
 
@@ -51,27 +61,103 @@ do {								\
         __init_rwsem((sem), #sem, &__key);                      \
 } while (0)
 
-extern void __down_read(struct rw_semaphore *sem);
-extern int __down_read_trylock(struct rw_semaphore *sem);
-extern void __down_write(struct rw_semaphore *sem);
-extern int __down_write_trylock(struct rw_semaphore *sem);
-extern void __up_read(struct rw_semaphore *sem);
-extern void __up_write(struct rw_semaphore *sem);
-extern void __downgrade_write(struct rw_semaphore *sem);
+/*
+ * lock for reading
+ */
+static inline void __down_read(struct rw_semaphore *sem)
+{
+        if (unlikely(atomic64_inc_return((atomic64_t *)(&sem->count)) <= 0L))
+                rwsem_down_read_failed(sem);
+}
+
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+        long tmp;
+
+        while ((tmp = sem->count) >= 0L) {
+                if (tmp == cmpxchg(&sem->count, tmp,
+                                   tmp + RWSEM_ACTIVE_READ_BIAS)) {
+                        return 1;
+                }
+        }
+        return 0;
+}
 
+/*
+ * lock for writing
+ */
 static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
 {
-        __down_write(sem);
+        long tmp;
+
+        tmp = atomic64_add_return(RWSEM_ACTIVE_WRITE_BIAS,
+                                  (atomic64_t *)(&sem->count));
+        if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))
+                rwsem_down_write_failed(sem);
 }
 
-static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
+static inline void __down_write(struct rw_semaphore *sem)
 {
-        return atomic_add_return(delta, (atomic_t *)(&sem->count));
+        __down_write_nested(sem, 0);
+}
+
+static inline int __down_write_trylock(struct rw_semaphore *sem)
+{
+        long tmp;
+
+        tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
+                      RWSEM_ACTIVE_WRITE_BIAS);
+        return tmp == RWSEM_UNLOCKED_VALUE;
 }
 
-static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+        long tmp;
+
+        tmp = atomic64_dec_return((atomic64_t *)(&sem->count));
+        if (unlikely(tmp < -1L && (tmp & RWSEM_ACTIVE_MASK) == 0L))
+                rwsem_wake(sem);
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+        if (unlikely(atomic64_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
+                                         (atomic64_t *)(&sem->count)) < 0L))
+                rwsem_wake(sem);
+}
+
+/*
+ * implement atomic add functionality
+ */
+static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
+{
+        atomic64_add(delta, (atomic64_t *)(&sem->count));
+}
+
+/*
+ * downgrade write lock to read lock
+ */
+static inline void __downgrade_write(struct rw_semaphore *sem)
+{
+        long tmp;
+
+        tmp = atomic64_add_return(-RWSEM_WAITING_BIAS, (atomic64_t *)(&sem->count));
+        if (tmp < 0L)
+                rwsem_downgrade_wake(sem);
+}
+
+/*
+ * implement exchange and add functionality
+ */
+static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
 {
-        atomic_add(delta, (atomic_t *)(&sem->count));
+        return atomic64_add_return(delta, (atomic64_t *)(&sem->count));
 }
 
 static inline int rwsem_is_locked(struct rw_semaphore *sem)