V4L/DVB (11044): v4l2-device: add v4l2_device_disconnect

Call v4l2_device_disconnect when the parent of a hotpluggable device
disconnects. This ensures that you do not have a pointer to a device that
is no longer present.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/video4linux/CARDLIST.bttv

@@ -157,4 +157,3 @@
 156 -> IVCE-8784                                           [0000:f050,0001:f050,0002:f050,0003:f050]
 157 -> Geovision GV-800(S) (master)                        [800a:763d]
 158 -> Geovision GV-800(S) (slave)                         [800b:763d,800c:763d,800d:763d]
-159 -> ProVideo PV183                                      [1830:1540,1831:1540,1832:1540,1833:1540,1834:1540,1835:1540,1836:1540,1837:1540]

Documentation/video4linux/v4l2-framework.txt

@@ -105,6 +105,17 @@ You unregister with:
 
 Unregistering will also automatically unregister all subdevs from the device.
 
+If you have a hotpluggable device (e.g. a USB device), then when a disconnect
+happens the parent device becomes invalid. Since v4l2_device has a pointer to
+that parent device it has to be cleared as well to mark that the parent is
+gone. To do this call:
+
+	v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
+
+This does *not* unregister the subdevs, so you still need to call the
+v4l2_device_unregister() function for that. If your driver is not hotpluggable,
+then there is no need to call v4l2_device_disconnect().
+
 Sometimes you need to iterate over all devices registered by a specific
 driver. This is usually the case if multiple device drivers use the same
 hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv