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

[Daniel Scally <djrscally@gmail.com>]

Hi Laurent

On 14/12/2021 22:22, Laurent Pinchart wrote:
> Hi Daniel,
> 
> Thank you for the patch.
> 
> 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.

>> +					   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;
>