parisc: Release spinlocks using ordered store

This patch updates the spin unlock code to use an ordered store with
release semanatics.  All prior accesses are guaranteed to be performed
before an ordered store is performed.

Using an ordered store is significantly faster than using the sync
memory barrier.
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/spinlock.h

@@ -37,8 +37,8 @@ static inline void arch_spin_unlock(arch_spinlock_t *x)
 	volatile unsigned int *a;
 
 	a = __ldcw_align(x);
-	mb();
-	*a = 1;
+	/* Release with ordered store. */
+	__asm__ __volatile__("stw,ma %0,0(%1)" : : "r"(1), "r"(a) : "memory");
 }
 
 static inline int arch_spin_trylock(arch_spinlock_t *x)

arch/parisc/kernel/syscall.S

@@ -640,8 +640,7 @@ cas_action:
 	sub,<>	%r28, %r25, %r0
 2:	stw	%r24, 0(%r26)
 	/* Free lock */
-	sync
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)
 #if ENABLE_LWS_DEBUG
 	/* Clear thread register indicator */
 	stw	%r0, 4(%sr2,%r20)
@@ -655,8 +654,7 @@ cas_action:
 3:		
 	/* Error occurred on load or store */
 	/* Free lock */
-	sync
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)
 #if ENABLE_LWS_DEBUG
 	stw	%r0, 4(%sr2,%r20)
 #endif
@@ -857,8 +855,7 @@ cas2_action:
 
 cas2_end:
 	/* Free lock */
-	sync
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)
 	/* Enable interrupts */
 	ssm	PSW_SM_I, %r0
 	/* Return to userspace, set no error */
@@ -868,8 +865,7 @@ cas2_end:
 22:
 	/* Error occurred on load or store */
 	/* Free lock */
-	sync
-	stw	%r20, 0(%sr2,%r20)
+	stw,ma	%r20, 0(%sr2,%r20)
 	ssm	PSW_SM_I, %r0
 	ldo	1(%r0),%r28
 	b	lws_exit