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| -rw-r--r-- | Documentation/driver-api/media/v4l2-subdev.rst | 86 |
1 files changed, 45 insertions, 41 deletions
diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst index 3adcd881cae5..d3e0fd6652b0 100644 --- a/Documentation/driver-api/media/v4l2-subdev.rst +++ b/Documentation/driver-api/media/v4l2-subdev.rst @@ -182,7 +182,51 @@ You can unregister a sub-device using: Afterwards the subdev module can be unloaded and :c:type:`sd <v4l2_subdev>`->dev == ``NULL``. -You can call an ops function either directly: +In the **asynchronous** case subdevice probing can be invoked independently of +the bridge driver availability. The subdevice driver then has to verify whether +all the requirements for a successful probing are satisfied. This can include a +check for a master clock availability. If any of the conditions aren't satisfied +the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing +attempts. Once all conditions are met the subdevice shall be registered using +the :c:func:`v4l2_async_register_subdev` function. Unregistration is +performed using the :c:func:`v4l2_async_unregister_subdev` call. Subdevices +registered this way are stored in a global list of subdevices, ready to be +picked up by bridge drivers. + +Bridge drivers in turn have to register a notifier object. This is +performed using the :c:func:`v4l2_async_notifier_register` call. To +unregister the notifier the driver has to call +:c:func:`v4l2_async_notifier_unregister`. The former of the two functions +takes two arguments: a pointer to struct :c:type:`v4l2_device` and a +pointer to struct :c:type:`v4l2_async_notifier`. + +Before registering the notifier, bridge drivers must do two things: +first, the notifier must be initialized using the +:c:func:`v4l2_async_notifier_init`. Second, bridge drivers can then +begin to form a list of subdevice descriptors that the bridge device +needs for its operation. Subdevice descriptors are added to the notifier +using the :c:func:`v4l2_async_notifier_add_subdev` call. This function +takes two arguments: a pointer to struct :c:type:`v4l2_async_notifier`, +and a pointer to the subdevice descripter, which is of type struct +:c:type:`v4l2_async_subdev`. + +The V4L2 core will then use these descriptors to match asynchronously +registered subdevices to them. If a match is detected the ``.bound()`` +notifier callback is called. After all subdevices have been located the +.complete() callback is called. When a subdevice is removed from the +system the .unbind() method is called. All three callbacks are optional. + +Calling subdev operations +~~~~~~~~~~~~~~~~~~~~~~~~~ + +The advantage of using :c:type:`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 +controlled through GPIO pins. This distinction is only relevant when setting +up the device, but once the subdev is registered it is completely transparent. + +Once te subdev has been registered you can call an ops function either +directly: .. code-block:: c @@ -235,46 +279,6 @@ 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 :c:type:`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 -controlled through GPIO pins. This distinction is only relevant when setting -up the device, but once the subdev is registered it is completely transparent. - -In the **asynchronous** case subdevice probing can be invoked independently of -the bridge driver availability. The subdevice driver then has to verify whether -all the requirements for a successful probing are satisfied. This can include a -check for a master clock availability. If any of the conditions aren't satisfied -the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing -attempts. Once all conditions are met the subdevice shall be registered using -the :c:func:`v4l2_async_register_subdev` function. Unregistration is -performed using the :c:func:`v4l2_async_unregister_subdev` call. Subdevices -registered this way are stored in a global list of subdevices, ready to be -picked up by bridge drivers. - -Bridge drivers in turn have to register a notifier object. This is -performed using the :c:func:`v4l2_async_notifier_register` call. To -unregister the notifier the driver has to call -:c:func:`v4l2_async_notifier_unregister`. The former of the two functions -takes two arguments: a pointer to struct :c:type:`v4l2_device` and a -pointer to struct :c:type:`v4l2_async_notifier`. - -Before registering the notifier, bridge drivers must do two things: -first, the notifier must be initialized using the -:c:func:`v4l2_async_notifier_init`. Second, bridge drivers can then -begin to form a list of subdevice descriptors that the bridge device -needs for its operation. Subdevice descriptors are added to the notifier -using the :c:func:`v4l2_async_notifier_add_subdev` call. This function -takes two arguments: a pointer to struct :c:type:`v4l2_async_notifier`, -and a pointer to the subdevice descripter, which is of type struct -:c:type:`v4l2_async_subdev`. - -The V4L2 core will then use these descriptors to match asynchronously -registered subdevices to them. If a match is detected the ``.bound()`` -notifier callback is called. After all subdevices have been located the -.complete() callback is called. When a subdevice is removed from the -system the .unbind() method is called. All three callbacks are optional. - V4L2 sub-device userspace API ----------------------------- |