Introduce ancillary links

Hello all

At present there's no means in the kernel of describing the supporting
relationship between subdevices that work together to form an effective single
unit - the type example in this case being a camera sensor and its
corresponding vcm. To attempt to solve that, this series adds a new type of
media link called MEDIA_LNK_FL_ANCILLARY_LINK, which connects two instances of
struct media_entity.

The mechanism of connection I have modelled as a notifier and async subdev,
which seemed the best route since sensor drivers already typically will call
v4l2_async_register_subdev_sensor() on probe, and that function already looks
for a reference to a firmware node with the reference named "lens-focus". To
avoid boilerplate in the sensor drivers, I added some new functions in
v4l2-async that are called in v4l2_async_match_notify() to create the ancillary
links. I haven't gone further than that yet, but I suspect we could cut down on
code elsewhere by, for example, also creating pad-to-pad links in the same place

Series level changes since v2:

  - Squashed #2 and #3

Series-level changes since v1:

	- New patch adding some documentation to the uAPI pages.

Dan


Daniel Scally (5):
  media: entity: Skip non-data links in graph iteration
  media: media.h: Add new media link type
  media: entity: Add link_type_name() helper
  media: entity: Add support for ancillary links
  media: v4l2-async: Create links during v4l2_async_match_notify()

 .../media/mediactl/media-controller-model.rst |  6 +++
 .../media/mediactl/media-types.rst            | 17 +++++--
 drivers/media/mc/mc-entity.c                  | 46 +++++++++++++++++--
 drivers/media/v4l2-core/v4l2-async.c          | 31 +++++++++++++
 include/media/media-entity.h                  | 19 ++++++++
 include/uapi/linux/media.h                    |  1 +
 6 files changed, 112 insertions(+), 8 deletions(-)

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2.25.1