Hi Mauro

On 15/12/2021 09:25, Mauro Carvalho Chehab wrote:

Em Mon, 13 Dec 2021 23:28:44 +0000
Daniel Scally [off-list ref] escreveu:

quoted

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 - checking the entity.function of both notifier and subdev to make sure
that's appropriate. 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.

Thoughts and comments very welcome 

The idea of ancillary link sounds interesting. I did a quick look at
the series. 

Laurent already did some good points during his review.
Besides that, one thing it is missing, though, is an implementation on
a driver. At least vimc should gain an implementation at this series,
in order to allow media developers to test and see how the graph will
be after the patch series.

We have this running through libcamera at the moment; this series piggy
backs onto the notifier that's set up by
v4l2_async_create_sensor_subdev() so that the connection is made and the
links created when a lens controller is linked to the sensor via the
lens-focus firmware property. I've been testing this using the dw9719
driver I posted [1], plus a series that adds support to libcamera [2]. I
believe that some folks from Cros have also tested it with the dw9714
driver too.


[1]
https://lore.kernel.org/linux-media/20211128232115.38833-1-djrscally@gmail.com/ (local)

[2]
https://lists.libcamera.org/pipermail/libcamera-devel/2021-December/028082.html

Regards,
Mauro

quoted

Dan

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

 drivers/media/mc/mc-entity.c         | 56 ++++++++++++++++++++++++++--
 drivers/media/v4l2-core/v4l2-async.c | 51 +++++++++++++++++++++++++
 include/media/media-entity.h         | 29 ++++++++++++++
 include/uapi/linux/media.h           |  1 +
 4 files changed, 134 insertions(+), 3 deletions(-)

Thanks,
Mauro