drm/qxl: move qxl_primary_apply_cursor to correct place

The qxl device ties the cursor to the primary surface.  Therefore
calling qxl_io_destroy_primary() and qxl_io_create_primary() to switch
the framebuffer causes the cursor information being lost and the driver
must re-apply it.

The correct call order to do that is qxl_io_destroy_primary() +
qxl_io_create_primary() + qxl_primary_apply_cursor().

The old code did qxl_io_destroy_primary() + qxl_primary_apply_cursor() +
qxl_io_create_primary().  Due to qxl_primary_apply_cursor request being
queued in a ringbuffer and qxl_io_create_primary() trapping to the
hypervisor instantly there is a high chance that qxl_io_create_primary()
is processed first even with the wrong call order.  But it's racy and
thus not reliable.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-11-kraxel@redhat.com

drivers/gpu/drm/qxl/qxl_display.c

@@ -533,7 +533,6 @@ static void qxl_primary_atomic_update(struct drm_plane *plane,
 	    .x2 = plane->state->fb->width,
 	    .y2 = plane->state->fb->height
 	};
-	int ret;
 	bool same_shadow = false;
 
 	if (old_state->fb) {
@@ -554,16 +553,13 @@ static void qxl_primary_atomic_update(struct drm_plane *plane,
 		if (!same_shadow)
 			qxl_io_destroy_primary(qdev);
 		bo_old->is_primary = false;
-
-		ret = qxl_primary_apply_cursor(plane);
-		if (ret)
-			DRM_ERROR(
-			"could not set cursor after creating primary");
 	}
 
 	if (!bo->is_primary) {
-		if (!same_shadow)
+		if (!same_shadow) {
 			qxl_io_create_primary(qdev, 0, bo);
+			qxl_primary_apply_cursor(plane);
+		}
 		bo->is_primary = true;
 	}