[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>

2 files changed, 3 insertions, 37 deletions

diff --git a/arch/ppc64/kernel/ItLpQueue.c b/arch/ppc64/kernel/ItLpQueue.c
index a4f32cbf5297..4231861288a3 100644
--- a/arch/ppc64/kernel/ItLpQueue.c
+++ b/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)
diff --git a/include/asm-ppc64/iSeries/ItLpQueue.h b/include/asm-ppc64/iSeries/ItLpQueue.h
index 51db08852dba..69b26ad74135 100644
--- a/include/asm-ppc64/iSeries/ItLpQueue.h
+++ b/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;