Re: [RFC PATCH 0/2] Introduce ancillary links

[Daniel Scally <djrscally@gmail.com>]

On 26/11/2021 02:59, Laurent Pinchart wrote:
> On Fri, Nov 26, 2021 at 12:16:01AM +0000, Daniel Scally wrote:
>> Hello all
>>
>> This series is not yet ready to merge, but I wanted to share it as I know some
>> other folks are working in similar areas at the moment (and I am including the
>> libcamera devel list for the same reason)
> Seems you forgot to CC libcamera-devel :-) Let's fix that on v2.


Argh! Sorry, will do

>> 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. Further work would be needed to document it properly, and
>> there may be ramifications within the v4l2-core which I have not yet discovered
>> (a lot of places seem to assume that media_entity->links means pad-2-pad links,
>> so some extra work might be needed to validate the link type before doing any
>> thing to them).
>>
>> 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 :)
>>
>> Dan
>>
>> Daniel Scally (2):
>>   media: entity: Add support for ancillary links
>>   media: v4l2-async: Create links during v4l2_async_match_notify()
>>
>>  drivers/media/mc/mc-entity.c         | 30 ++++++++++++++++
>>  drivers/media/v4l2-core/v4l2-async.c | 51 ++++++++++++++++++++++++++++
>>  include/media/media-entity.h         | 30 ++++++++++++++++
>>  include/uapi/linux/media.h           |  1 +
>>  4 files changed, 112 insertions(+)
>>