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

drivers/media/video/v4l2-device.c

@@ -49,19 +49,26 @@ int v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev)
 }
 EXPORT_SYMBOL_GPL(v4l2_device_register);
 
+void v4l2_device_disconnect(struct v4l2_device *v4l2_dev)
+{
+	if (v4l2_dev->dev) {
+		dev_set_drvdata(v4l2_dev->dev, NULL);
+		v4l2_dev->dev = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(v4l2_device_disconnect);
+
 void v4l2_device_unregister(struct v4l2_device *v4l2_dev)
 {
 	struct v4l2_subdev *sd, *next;
 
 	if (v4l2_dev == NULL)
 		return;
-	if (v4l2_dev->dev)
-		dev_set_drvdata(v4l2_dev->dev, NULL);
+	v4l2_device_disconnect(v4l2_dev);
+
 	/* Unregister subdevs */
 	list_for_each_entry_safe(sd, next, &v4l2_dev->subdevs, list)
 		v4l2_device_unregister_subdev(sd);
-
-	v4l2_dev->dev = NULL;
 }
 EXPORT_SYMBOL_GPL(v4l2_device_unregister);
 

include/media/v4l2-device.h

@@ -53,7 +53,11 @@ struct v4l2_device {
    dev may be NULL in rare cases (ISA devices). In that case you
    must fill in the v4l2_dev->name field before calling this function. */
 int __must_check v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
-/* Set v4l2_dev->dev->driver_data to NULL and unregister all sub-devices */
+/* Set v4l2_dev->dev to NULL. Call when the USB parent disconnects.
+   Since the parent disappears this ensures that v4l2_dev doesn't have an
+   invalid parent pointer. */
+void v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
+/* Unregister all sub-devices and any other resources related to v4l2_dev. */
 void v4l2_device_unregister(struct v4l2_device *v4l2_dev);
 
 /* Register a subdev with a v4l2 device. While registered the subdev module