Add documentation about centrally managed subdev state. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> --- .../driver-api/media/v4l2-subdev.rst | 25 +++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/Documentation/driver-api/media/v4l2-subdev.rst b/Documentation/driver-api/media/v4l2-subdev.rst index 7736da077fb8..b28607c3fc79 100644 --- a/Documentation/driver-api/media/v4l2-subdev.rst +++ b/Documentation/driver-api/media/v4l2-subdev.rst @@ -518,6 +518,31 @@ 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, on entry for each pad. + +In addition to the active configuration, each subdev filehandle has contained +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_alloc_state() to initialize the active state between calls to +media_entity_pads_init() and v4l2_*_register_subdev(). + +The active state must be locked before access, and can be done with e.g. +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 all the subdev drivers do not comply with this yet, and may +pass NULL for the ACTIVE case, so the called subdev ops must also handle the +NULL case. This can be easily managed by the helpers +v4l2_subdev_validate_state() or v4l2_subdev_validate_and_lock_state(). + V4L2 sub-device functions and data structures --------------------------------------------- -- 2.25.1
