[media] v4l: subdev: Control ioctls support

Pass the control-related ioctls to the subdev driver through the control
framework.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt
index 8b35871..1feecfc 100644
--- a/Documentation/video4linux/v4l2-framework.txt
+++ b/Documentation/video4linux/v4l2-framework.txt
@@ -334,6 +334,22 @@
 v4l2_device_register_subdev_nodes(). Those device nodes will be automatically
 removed when sub-devices are unregistered.
 
+The device node handles a subset of the V4L2 API.
+
+VIDIOC_QUERYCTRL
+VIDIOC_QUERYMENU
+VIDIOC_G_CTRL
+VIDIOC_S_CTRL
+VIDIOC_G_EXT_CTRLS
+VIDIOC_S_EXT_CTRLS
+VIDIOC_TRY_EXT_CTRLS
+
+	The controls ioctls are identical to the ones defined in V4L2. They
+	behave identically, with the only exception that they deal only with
+	controls implemented in the sub-device. Depending on the driver, those
+	controls can be also be accessed through one (or several) V4L2 device
+	nodes.
+
 
 I2C sub-device drivers
 ----------------------