drm/radeon/kms: wait for gpu idle before changing power mode

set proper wait condition as noted by Rafał Miłecki.
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_pm.c

@@ -378,6 +378,16 @@ static void radeon_pm_set_clocks(struct radeon_device *rdev)
 	radeon_get_power_state(rdev, rdev->pm.planned_action);
 	mutex_lock(&rdev->cp.mutex);
 
+	/* wait for GPU idle */
+	rdev->pm.gui_idle = false;
+	rdev->irq.gui_idle = true;
+	radeon_irq_set(rdev);
+	wait_event_interruptible_timeout(
+		rdev->irq.idle_queue, rdev->pm.gui_idle,
+		msecs_to_jiffies(RADEON_WAIT_IDLE_TIMEOUT));
+	rdev->irq.gui_idle = false;
+	radeon_irq_set(rdev);
+
 	if (rdev->pm.active_crtcs & (1 << 0)) {
 		rdev->pm.req_vblank |= (1 << 0);
 		drm_vblank_get(rdev->ddev, 0);