drm/sun4i: Implement drm_driver lastclose to restore fbdev console

commit 2a596fc9 upstream.

The drm_driver lastclose callback is called when the last userspace
DRM client has closed. Call drm_fbdev_cma_restore_mode to restore
the fbdev console otherwise the fbdev console will stop working.

Fixes: 9026e0d1 ("drm: Add Allwinner A10 Display Engine support")
Tested-by: Olliver Schinagl <oliver@schinagl.nl>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[net147@gmail.com: Backport to 4.9, minor context change]
Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/sun4i/sun4i_drv.c

@@ -47,6 +47,13 @@ static void sun4i_drv_disable_vblank(struct drm_device *drm, unsigned int pipe)
 	sun4i_tcon_enable_vblank(tcon, false);
 }
 
+static void sun4i_drv_lastclose(struct drm_device *dev)
+{
+	struct sun4i_drv *drv = dev->dev_private;
+
+	drm_fbdev_cma_restore_mode(drv->fbdev);
+}
+
 static const struct file_operations sun4i_drv_fops = {
 	.owner		= THIS_MODULE,
 	.open		= drm_open,
@@ -65,6 +72,7 @@ static struct drm_driver sun4i_drv_driver = {
 	.driver_features	= DRIVER_GEM | DRIVER_MODESET | DRIVER_PRIME | DRIVER_ATOMIC,
 
 	/* Generic Operations */
+	.lastclose		= sun4i_drv_lastclose,
 	.fops			= &sun4i_drv_fops,
 	.name			= "sun4i-drm",
 	.desc			= "Allwinner sun4i Display Engine",