On 05/10/2021 10:57, Tomi Valkeinen wrote: > 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..c3fd57fff668 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 contained s/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_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 can be done with and -> and that > +v4l2_subdev_lock_state() or v4l2_subdev_lock_active_state(). Note my review of patch 4 regarding the naming of these functions. > + > +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 all the subdev drivers do not comply -> not all the subdev drivers comply > +NULL for the ACTIVE case. This is only a problem for subdev drivers which use > +the cetrally managed active state and are used in media pipelines with older cetrally -> centrally > +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 > --------------------------------------------- > > Regards, Hans
