[libcamera-devel] [PATCH 0/5] Introduce ancillary links

[Laurent Pinchart]

Hi Mauro,

On Wed, Dec 15, 2021 at 10:25:09AM +0100, Mauro Carvalho Chehab wrote:
> Em Mon, 13 Dec 2021 23:28:44 +0000 Daniel Scally escreveu:
> 
> > 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.

The whole point of patch 4/4 is to create those links in the core
without requiring manual involvement of the drivers :-)

> > 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(-)

-- 
Regards,

Laurent Pinchart