dri1: Add a macro to validate two dri drawables in one go.

Dri drivers often may validate first a write drawable and then a read
drawable ("readable"). However, the hardware lock may be unlocked when
validating the readable, causing the write drawable status to be stale.

Drivers should use this macro instead when validating two drawables.

src/mesa/drivers/dri/common/dri_util.h

@@ -108,6 +108,28 @@ do {                                                                    \
     }                                                                   \
 } while (0)
 
+/**
+ * Same as above, but for two drawables simultaneously.
+ *
+ */
+
+#define DRI_VALIDATE_TWO_DRAWABLES_INFO(psp, pdp, prp)			\
+do {								\
+    while (*((pdp)->pStamp) != (pdp)->lastStamp ||			\
+	   *((prp)->pStamp) != (prp)->lastStamp) {			\
+        register unsigned int hwContext = (psp)->pSAREA->lock.lock &	\
+	    ~(DRM_LOCK_HELD | DRM_LOCK_CONT);				\
+	DRM_UNLOCK((psp)->fd, &(psp)->pSAREA->lock, hwContext);		\
+									\
+	DRM_SPINLOCK(&(psp)->pSAREA->drawable_lock, (psp)->drawLockID);	\
+	DRI_VALIDATE_DRAWABLE_INFO_ONCE(pdp);                           \
+	DRI_VALIDATE_DRAWABLE_INFO_ONCE(prp);				\
+	DRM_SPINUNLOCK(&(psp)->pSAREA->drawable_lock, (psp)->drawLockID); \
+									\
+	DRM_LIGHT_LOCK((psp)->fd, &(psp)->pSAREA->lock, hwContext);	\
+    }                                                                   \
+} while (0)
+
 
 /**
  * Driver callback functions.