[PATCH] ppc64: Replace custom locking code with a spinlock

The hvlpevent_queue (formally ItLpQueue) has a member called xInUseWord
which is used for serialising access to the queue. Because it's a word
(ie. 32 bit) there's a custom 32-bit version of test_and_set_bit() or
thereabouts in ItLpQueue.c.

The xInUseWord is not shared with they hypervisor, so we can replace it
with a spinlock and remove the custom code.

There is also another locking mechanism (ItLpQueueInProcess). This is
redundant because it's only manipulated while the lock's held. Remove it.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/ppc64/kernel/ItLpQueue.c

@@ -42,35 +42,8 @@ static char *event_types[HvLpEvent_Type_NumTypes] = {
 	"Virtual I/O"
 };
 
-static __inline__ int set_inUse(void)
-{
-	int t;
-	u32 * inUseP = &hvlpevent_queue.xInUseWord;
-
-	__asm__ __volatile__("\n\
-1:	lwarx	%0,0,%2		\n\
-	cmpwi	0,%0,0		\n\
-	li	%0,0		\n\
-	bne-	2f		\n\
-	addi	%0,%0,1		\n\
-	stwcx.	%0,0,%2		\n\
-	bne-	1b		\n\
-2:	eieio"
-	: "=&r" (t), "=m" (hvlpevent_queue.xInUseWord)
-	: "r" (inUseP), "m" (hvlpevent_queue.xInUseWord)
-	: "cc");
-
-	return t;
-}
-
-static __inline__ void clear_inUse(void)
-{
-	hvlpevent_queue.xInUseWord = 0;
-}
-
 /* Array of LpEvent handler functions */
 extern LpEventHandler lpEventHandler[HvLpEvent_Type_NumTypes];
-unsigned long ItLpQueueInProcess = 0;
 
 static struct HvLpEvent * get_next_hvlpevent(void)
 {
@@ -144,14 +117,9 @@ void process_hvlpevents(struct pt_regs *regs)
 	struct HvLpEvent * event;
 
 	/* If we have recursed, just return */
-	if ( !set_inUse() )
+	if (!spin_trylock(&hvlpevent_queue.lock))
 		return;
 
-	if (ItLpQueueInProcess == 0)
-		ItLpQueueInProcess = 1;
-	else
-		BUG();
-
 	for (;;) {
 		event = get_next_hvlpevent();
 		if (event) {
@@ -187,9 +155,7 @@ void process_hvlpevents(struct pt_regs *regs)
 			break;
 	}
 
-	ItLpQueueInProcess = 0;
-	mb();
-	clear_inUse();
+	spin_unlock(&hvlpevent_queue.lock);
 }
 
 static int set_spread_lpevents(char *str)

include/asm-ppc64/iSeries/ItLpQueue.h

@@ -69,7 +69,7 @@ struct hvlpevent_queue {
 	char	*xSlicEventStackPtr;	// 0x20
 	u8	xIndex;			// 0x28 unique sequential index.
 	u8	xSlicRsvd[3];		// 0x29-2b
-	u32	xInUseWord;		// 0x2C
+	spinlock_t	lock;
 };
 
 extern struct hvlpevent_queue hvlpevent_queue;