v4l2-device: add a notify callback.

From: Hans Verkuil <hverkuil@xs4all.nl>

Add a notify callback to v4l2_device to let sub-devices notify their
parent of special events.

Priority: normal

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

1 files changed, 10 insertions, 0 deletions

diff --git a/linux/Documentation/video4linux/v4l2-framework.txt b/linux/Documentation/video4linux/v4l2-framework.txt
index accc376e9..1232f3066 100644
--- a/linux/Documentation/video4linux/v4l2-framework.txt
+++ b/linux/Documentation/video4linux/v4l2-framework.txt
@@ -93,6 +93,11 @@ The first 'dev' argument is normally the struct device pointer of a pci_dev,
 usb_device or platform_device. It is rare for dev to be NULL, but it happens
 with ISA devices, for example.
 
+You can also supply a notify() callback that can be called by sub-devices to
+notify you of events. Whether you need to set this depends on the sub-device.
+Any notifications a sub-device supports must be defined in a header in
+include/media/<subdevice>.h.
+
 You unregister with:
 
 	v4l2_device_unregister(struct v4l2_device *v4l2_dev);
@@ -280,6 +285,11 @@ e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
 v4l2_device_call_all(). That ensures that it will only go to the subdev
 that needs it.
 
+If the sub-device needs to notify its v4l2_device parent of an event, then
+it can call v4l2_subdev_notify(sd, notification, arg). This macro checks
+whether there is a notify() callback defined and returns -ENODEV if not.
+Otherwise the result of the notify() call is returned.
+
 The advantage of using v4l2_subdev is that it is a generic struct and does
 not contain any knowledge about the underlying hardware. So a driver might
 contain several subdevs that use an I2C bus, but also a subdev that is