drm/vmwgfx: Reorganize the fence wait loop

Reorganize the fence wait loop somewhat to make it look more like the
examples in set_current_state() kerneldoc, and add some code comments.

Also if we're about to time out, make sure we check again whether the fence
is actually signaled.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Deepak Rawat <drawat@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c

@@ -175,7 +175,6 @@ static long vmw_fence_wait(struct dma_fence *f, bool intr, signed long timeout)
 	struct vmw_private *dev_priv = fman->dev_priv;
 	struct vmwgfx_wait_cb cb;
 	long ret = timeout;
-	unsigned long irq_flags;
 
 	if (likely(vmw_fence_obj_signaled(fence)))
 		return timeout;
@@ -183,7 +182,7 @@ static long vmw_fence_wait(struct dma_fence *f, bool intr, signed long timeout)
 	vmw_fifo_ping_host(dev_priv, SVGA_SYNC_GENERIC);
 	vmw_seqno_waiter_add(dev_priv);
 
-	spin_lock_irqsave(f->lock, irq_flags);
+	spin_lock(f->lock);
 
 	if (intr && signal_pending(current)) {
 		ret = -ERESTARTSYS;
@@ -194,30 +193,45 @@ static long vmw_fence_wait(struct dma_fence *f, bool intr, signed long timeout)
 	cb.task = current;
 	list_add(&cb.base.node, &f->cb_list);
 
-	while (ret > 0) {
+	for (;;) {
 		__vmw_fences_update(fman);
-		if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &f->flags))
-			break;
 
+		/*
+		 * We can use the barrier free __set_current_state() since
+		 * DMA_FENCE_FLAG_SIGNALED_BIT + wakeup is protected by the
+		 * fence spinlock.
+		 */
 		if (intr)
 			__set_current_state(TASK_INTERRUPTIBLE);
 		else
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-		spin_unlock_irqrestore(f->lock, irq_flags);
 
-		ret = schedule_timeout(ret);
+		if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &f->flags)) {
+			if (ret == 0 && timeout > 0)
+				ret = 1;
+			break;
+		}
 
-		spin_lock_irqsave(f->lock, irq_flags);
-		if (ret > 0 && intr && signal_pending(current))
+		if (intr && signal_pending(current)) {
 			ret = -ERESTARTSYS;
+			break;
 		}
 
+		if (ret == 0)
+			break;
+
+		spin_unlock(f->lock);
+
+		ret = schedule_timeout(ret);
+
+		spin_lock(f->lock);
+	}
+	__set_current_state(TASK_RUNNING);
 	if (!list_empty(&cb.base.node))
 		list_del(&cb.base.node);
-	__set_current_state(TASK_RUNNING);
 
 out:
-	spin_unlock_irqrestore(f->lock, irq_flags);
+	spin_unlock(f->lock);
 
 	vmw_seqno_waiter_remove(dev_priv);