IB/ipath: Fix sendctrl locking

Code review pointed out that the locking around uses of ipath_sendctrl 
and kr_sendctrl were, in several places, incorrect and/or inconsistent.

Signed-off-by: John Gregor <john.gregor@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/ipath/ipath_ruc.c b/drivers/infiniband/hw/ipath/ipath_ruc.c
index 54c61a9..1b4f7e1 100644
--- a/drivers/infiniband/hw/ipath/ipath_ruc.c
+++ b/drivers/infiniband/hw/ipath/ipath_ruc.c
@@ -479,9 +479,14 @@
 
 static void want_buffer(struct ipath_devdata *dd)
 {
-	set_bit(IPATH_S_PIOINTBUFAVAIL, &dd->ipath_sendctrl);
+	unsigned long flags;
+
+	spin_lock_irqsave(&dd->ipath_sendctrl_lock, flags);
+	dd->ipath_sendctrl |= INFINIPATH_S_PIOINTBUFAVAIL;
 	ipath_write_kreg(dd, dd->ipath_kregs->kr_sendctrl,
 			 dd->ipath_sendctrl);
+	ipath_read_kreg64(dd, dd->ipath_kregs->kr_scratch);
+	spin_unlock_irqrestore(&dd->ipath_sendctrl_lock, flags);
 }
 
 /**