Add documentation about centrally managed subdev state. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> --- .../driver-api/media/v4l2-subdev.rst | 28 +++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst index 7736da077fb8..db012729f8e3 100644 --- a/Documentation/driver-api/media/v4l2-subdev.rst +++ b/Documentation/driver-api/media/v4l2-subdev.rst @@ -518,6 +518,34 @@ The :c:func:`v4l2_i2c_new_subdev` function will call :c:type:`i2c_board_info` structure using the ``client_type`` and the ``addr`` to fill it. +Centrally managed subdev active state +------------------------------------- + +Traditionally V4L2 subdev drivers maintained internal state for the active +configuration for the subdev. This is often implemented as an array of struct +v4l2_mbus_framefmt, one entry for each pad. + +In addition to the active configuration, each subdev filehandle has an array of +struct v4l2_subdev_pad_config, managed by V4L2 core, which contains the TRY +configuration. + +To simplify the subdev drivers the V4L2 subdev API now optionally supports a +centrally managed active configuration. A subdev driver must use +v4l2_subdev_init_finalize() to initialize the active state between calls to +media_entity_pads_init() and v4l2_*_register_subdev(), and must call +v4l2_subdev_cleanup() to free the state. + +The active state must be locked before access, and that can be done with +v4l2_subdev_lock_state() or v4l2_subdev_lock_active_state(). + +The V4L2 core will pass either the TRY or ACTIVE state to various subdev ops. +Unfortunately not all the subdev drivers comply with this yet, and may pass +NULL for the ACTIVE case. This is only a problem for subdev drivers which use +the centrally managed active state and are used in media pipelines with older +subdev drivers. In these cases the called subdev ops must also handle the NULL +case. This can be easily managed by the use of +v4l2_subdev_validate_and_lock_state() helper. + V4L2 sub-device functions and data structures --------------------------------------------- -- 2.25.1
