Re: [PATCH 5/5] media: v4l2-async: Create links during v4l2_async_match_notify()

Laurent Pinchart
2021-12-14T23:01:20Z

Hi Daniel,

On Tue, Dec 14, 2021 at 10:36:01PM +0000, Daniel Scally wrote:
> On 14/12/2021 22:22, Laurent Pinchart wrote:
> > On Mon, Dec 13, 2021 at 11:28:49PM +0000, Daniel Scally wrote:
> >> Upon an async fwnode match, there's some typical behaviour that the
> >> notifier and matching subdev will want to do. For example, a notifier
> >> representing a sensor matching to an async subdev representing its
> >> VCM will want to create an ancillary link to expose that relationship
> >> to userspace.
> >>
> >> To avoid lots of code in individual drivers, try to build these links
> >> within v4l2 core.
> >>
> >> Signed-off-by: Daniel Scally <djrscally@gmail.com>
> >> ---
> >> Changes since the rfc:
> >>
> >> - None
> >>
> >> drivers/media/v4l2-core/v4l2-async.c | 51 ++++++++++++++++++++++++++++
> >> 1 file changed, 51 insertions(+)
> >>
> >> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> >> index 0404267f1ae4..6575b1cbe95f 100644
> >> --- a/drivers/media/v4l2-core/v4l2-async.c
> >> +++ b/drivers/media/v4l2-core/v4l2-async.c
> >> @@ -275,6 +275,45 @@ v4l2_async_nf_try_complete(struct v4l2_async_notifier *notifier)
> >> static int
> >> v4l2_async_nf_try_all_subdevs(struct v4l2_async_notifier *notifier);
> >>
> >> +static int
> >> +__v4l2_async_create_ancillary_link(struct v4l2_async_notifier *notifier,
> >> + struct v4l2_subdev *sd)
> >> +{
> >> + struct media_link *link;
> >> +
> >> + if (sd->entity.function != MEDIA_ENT_F_LENS &&
> >> + sd->entity.function != MEDIA_ENT_F_FLASH)
> >> + return -EINVAL;
> >> +
> >> + link = media_create_ancillary_link(&notifier->sd->entity, &sd->entity,
> >
> > Is there a guarantee at this point that notifier->sd->entity has already
> > been registered with the media_device ? That's done by
> > media_device_register_entity() called from
> > v4l2_device_register_subdev().
>
> v4l2_async_match_notify() calls v4l2_device_register_subdev() before the
> point that I've added the call to v4l2_async_try_create_links(), so I
> think that's covered there.

It calls it on sd, not notifier->sd. It's the latter that concerns me.

> >> + MEDIA_LNK_FL_ENABLED |
> >> + MEDIA_LNK_FL_IMMUTABLE);
> >> +
> >> + return IS_ERR(link) ? PTR_ERR(link) : 0;
> >> +}
> >> +
> >> +/*
> >> + * Setup links on behalf of the notifier and subdev, where it's obvious what
> >
> > s/Setup/Create/ ("link setup" refers to another operation, enabling and
> > disabling links at runtime)
>
> Yes, good point; although that too is a piece of terminology I find a
> bit jarring to be honest; I would have named that function
> media_entity_configure_link()
>
> >> + * should be done. At the moment, we only support cases where the notifier
> >> + * is a sensor and the subdev is a lens.
> >
> > s/sensor/camera sensor/
> > s/lens/lens controller/
> >
> >> + *
> >> + * TODO: Setup pad links if the notifier's function is MEDIA_ENT_F_VID_IF_BRIDGE
> >> + * and the subdev's is MEDIA_ENT_F_CAM_SENSOR
> >> + */
> >> +static int v4l2_async_try_create_links(struct v4l2_async_notifier *notifier,
> >> + struct v4l2_subdev *sd)
> >> +{
> >> + if (!notifier->sd)
> >> + return 0;
> >> +
> >> + switch (notifier->sd->entity.function) {
> >> + case MEDIA_ENT_F_CAM_SENSOR:
> >> + return __v4l2_async_create_ancillary_link(notifier, sd);
> >> + default:
> >> + return 0;
> >> + }
> >> +}
> >> +
> >> static int v4l2_async_match_notify(struct v4l2_async_notifier *notifier,
> >> struct v4l2_device *v4l2_dev,
> >> struct v4l2_subdev *sd,
> >> @@ -293,6 +332,18 @@ static int v4l2_async_match_notify(struct v4l2_async_notifier *notifier,
> >> return ret;
> >> }
> >>
> >> + /*
> >> + * Depending of the function of the entities involved, we may want to
> >> + * create links between them (for example between a sensor and its lens
> >> + * or between a sensor's source pad and the connected device's sink
> >> + * pad)
> >
> > s/)/)./
> >
> >> + */
> >> + ret = v4l2_async_try_create_links(notifier, sd);
> >> + if (ret) {
> >> + v4l2_device_unregister_subdev(sd);
> >> + return ret;
> >> + }
> >> +
> >> /* Remove from the waiting list */
> >> list_del(&asd->list);
> >> sd->asd = asd;

--
Regards,

Laurent Pinchart