Re: [PATCH v5 1/2] media: Add obj_type field to struct media_entity

Mauro Carvalho Chehab
2016-03-23T10:35:58Z

Em Wed, 23 Mar 2016 10:45:55 +0200
Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> escreveu:

> Code that processes media entities can require knowledge of the
> structure type that embeds a particular media entity instance in order
> to cast the entity to the proper object type. This needs is shown by the
> presence of the is_media_entity_v4l2_io and is_media_entity_v4l2_subdev
> functions.
>
> The implementation of those two functions relies on the entity function
> field, which is both a wrong and an inefficient design, without even
> mentioning the maintenance issue involved in updating the functions
> every time a new entity function is added. Fix this by adding add an
> obj_type field to the media entity structure to carry the information.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
> drivers/media/media-device.c | 2 +
> drivers/media/v4l2-core/v4l2-dev.c | 1 +
> drivers/media/v4l2-core/v4l2-subdev.c | 1 +
> include/media/media-entity.h | 79 +++++++++++++++++++----------------
> 4 files changed, 46 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 4a97d92a7e7d..88d8de3b7a4f 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -580,6 +580,8 @@ int __must_check media_device_register_entity(struct media_device *mdev,
> "Entity type for entity %s was not initialized!\n",
> entity->name);
>
> + WARN_ON(entity->obj_type == MEDIA_ENTITY_TYPE_INVALID);
> +

This is not ok. There are valid cases where the entity is not embedded
on some other struct. That's the case of connectors/connections, for
example: a connector/connection entity doesn't need anything else but
struct media device.

Also, this is V4L2 specific. Neither ALSA nor DVB need to use container_of().
Actually, this won't even work there, as the entity is stored as a pointer,
and not as an embedded data.

So, if we're willing to do this, then it should, instead, create
something like:

struct embedded_media_entity {
struct media_entity entity;
enum media_entity_type obj_type;
};

And then replace the occurrences of embedded media_entity by
embedded_media_entity at the V4L2 subsystem only, in the places where
the struct is embeded on another one.

> /* Warn if we apparently re-register an entity */
> WARN_ON(entity->graph_obj.mdev != NULL);
> entity->graph_obj.mdev = mdev;
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index d8e5994cccf1..70b559d7ca80 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -735,6 +735,7 @@ static int video_register_media_controller(struct video_device *vdev, int type)
> if (!vdev->v4l2_dev->mdev)
> return 0;
>
> + vdev->entity.obj_type = MEDIA_ENTITY_TYPE_VIDEO_DEVICE;
> vdev->entity.function = MEDIA_ENT_F_UNKNOWN;
>
> switch (type) {
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index d63083803144..0fa60801a428 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -584,6 +584,7 @@ void v4l2_subdev_init(struct v4l2_subdev *sd, const struct v4l2_subdev_ops *ops)
> sd->host_priv = NULL;
> #if defined(CONFIG_MEDIA_CONTROLLER)
> sd->entity.name = sd->name;
> + sd->entity.obj_type = MEDIA_ENTITY_TYPE_V4L2_SUBDEV;
> sd->entity.function = MEDIA_ENT_F_V4L2_SUBDEV_UNKNOWN;
> #endif
> }
> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> index 6dc9e4e8cbd4..5cea57955a3a 100644
> --- a/include/media/media-entity.h
> +++ b/include/media/media-entity.h
> @@ -188,10 +188,41 @@ struct media_entity_operations {
> };
>
> /**
> + * enum media_entity_type - Media entity type
> + *
> + * @MEDIA_ENTITY_TYPE_INVALID:
> + * Invalid type, used to catch uninitialized fields.
> + * @MEDIA_ENTITY_TYPE_VIDEO_DEVICE:
> + * The entity is embedded in a struct video_device instance.
> + * @MEDIA_ENTITY_TYPE_V4L2_SUBDEV:
> + * The entity is embedded in a struct v4l2_subdev instance.
> + *
> + * Media entity objects are not instantiated directly,

As I said before, this is not true (nor even at V4L2 subsystem, due to
the connectors/connections).

As before, you should call this as:
enum embedded_media_entity_type

And then change the test to:

"Media entity objects declared via struct embedded_media_device are not
instantiated directly,"

and fix the text below accordingly.

> but the media entity
> + * structure is inherited by (through embedding) other subsystem-specific
> + * structures. The media entity type identifies the type of the subclass
> + * structure that implements a media entity instance.
> + *
> + * This allows runtime type identification of media entities and safe casting to
> + * the correct object type. For instance, a media entity structure instance
> + * embedded in a v4l2_subdev structure instance will have the type
> + * MEDIA_ENTITY_TYPE_V4L2_SUBDEV and can safely be cast to a v4l2_subdev
> + * structure using the container_of() macro.
> + *
> + * The MEDIA_ENTITY_TYPE_INVALID type should never be set as an entity type, it
> + * only serves to catch uninitialized fields when registering entities.
> + */
> +enum media_entity_type {
> + MEDIA_ENTITY_TYPE_INVALID,
> + MEDIA_ENTITY_TYPE_VIDEO_DEVICE,
> + MEDIA_ENTITY_TYPE_V4L2_SUBDEV,
> +};
> +
> +/**
> * struct media_entity - A media entity graph object.
> *
> * @graph_obj: Embedded structure containing the media object common data.
> * @name: Entity name.
> + * @obj_type: Type of the object that implements the media_entity.
> * @function: Entity main function, as defined in uapi/media.h
> * (MEDIA_ENT_F_*)
> * @flags: Entity flags, as defined in uapi/media.h (MEDIA_ENT_FL_*)
> @@ -220,6 +251,7 @@ struct media_entity_operations {
> struct media_entity {
> struct media_gobj graph_obj; /* must be first field in struct */
> const char *name;
> + enum media_entity_type obj_type;

See above. This doesn't below to the generic media entity struct,
but to an special type that is meant to be embedded on some places.

> u32 function;
> unsigned long flags;
>
> @@ -329,56 +361,29 @@ static inline u32 media_gobj_gen_id(enum media_gobj_type type, u64 local_id)
> }
>
> /**
> - * is_media_entity_v4l2_io() - identify if the entity main function
> - * is a V4L2 I/O
> - *
> + * is_media_entity_v4l2_io() - Check if the entity is a video_device
> * @entity: pointer to entity
> *
> - * Return: true if the entity main function is one of the V4L2 I/O types
> - * (video, VBI or SDR radio); false otherwise.
> + * Return: true if the entity is an instance of a video_device object and can
> + * safely be cast to a struct video_device using the container_of() macro, or
> + * false otherwise.
> */
> static inline bool is_media_entity_v4l2_io(struct media_entity *entity)
> {
> - if (!entity)
> - return false;
> -
> - switch (entity->function) {
> - case MEDIA_ENT_F_IO_V4L:
> - case MEDIA_ENT_F_IO_VBI:
> - case MEDIA_ENT_F_IO_SWRADIO:
> - return true;
> - default:
> - return false;
> - }
> + return entity && entity->obj_type == MEDIA_ENTITY_TYPE_VIDEO_DEVICE;
> }
>
> /**
> - * is_media_entity_v4l2_subdev - return true if the entity main function is
> - * associated with the V4L2 API subdev usage
> - *
> + * is_media_entity_v4l2_subdev() - Check if the entity is a v4l2_subdev
> * @entity: pointer to entity
> *
> - * This is an ancillary function used by subdev-based V4L2 drivers.
> - * It checks if the entity function is one of functions used by a V4L2 subdev,
> - * e. g. camera-relatef functions, analog TV decoder, TV tuner, V4L2 DSPs.
> + * Return: true if the entity is an instance of a v4l2_subdev object and can
> + * safely be cast to a struct v4l2_subdev using the container_of() macro, or
> + * false otherwise.
> */
> static inline bool is_media_entity_v4l2_subdev(struct media_entity *entity)
> {
> - if (!entity)
> - return false;
> -
> - switch (entity->function) {
> - case MEDIA_ENT_F_V4L2_SUBDEV_UNKNOWN:
> - case MEDIA_ENT_F_CAM_SENSOR:
> - case MEDIA_ENT_F_FLASH:
> - case MEDIA_ENT_F_LENS:
> - case MEDIA_ENT_F_ATV_DECODER:
> - case MEDIA_ENT_F_TUNER:
> - return true;
> -
> - default:
> - return false;
> - }
> + return entity && entity->obj_type == MEDIA_ENTITY_TYPE_V4L2_SUBDEV;
> }
>
> /**

--
Thanks,
Mauro