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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Hans,

On Wednesday 23 Mar 2016 15:05:41 Hans Verkuil wrote:
> On 03/23/2016 11:35 AM, Mauro Carvalho Chehab wrote:
> > Em Wed, 23 Mar 2016 10:45:55 +0200 Laurent Pinchart 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.
> 
> Once connectors are enabled, then we do need a MEDIA_ENTITY_TYPE_CONNECTOR
> or MEDIA_ENTITY_TYPE_STANDALONE or something along those lines.

MEDIA_ENTITY_TYPE_CONNECTOR would make sense, but only if we add a struct 
media_connector. I believe that can be a good idea, at least to simplify 
management of the entity and the connector pad(s).

> > 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.

That's sounds like a strange design decision at the very least. There can be 
valid cases that require creation of bare entities, but I don't think they 
should be that common.

> Any other subsystem that *does* embed this can use obj_type. If it doesn't
> embed it in anything, then MEDIA_ENTITY_TYPE_STANDALONE should be used (or
> whatever name we give it). I agree that we need a type define for the case
> where it is not embedded.

I'd like to point out that I had defined MEDIA_ENTITY_TYPE_MEDIA_ENTITY for 
that purpose in v4, and was requested to drop it.

I can submit a v6 with MEDIA_ENTITY_TYPE_MEDIA_ENTITY added back. I'd like a 
confirmation that it won't be rejected straight away though.

The WARN_ON() is in my opinion useful, but I'm ready to leave it out for now 
until we fix the connectors mess if it can help getting this patch merged 
faster.

> > 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;
> > };
> 
> It's not v4l2 specific. It is just that v4l2 is the only subsystem that
> requires this information at the moment. I see no reason at all to create
> such an ugly struct.

I totally agree.

> I very strongly suspect that other subsystems will also embed this in their
> own internal structs. I actually wonder why it isn't embedded in struct
> dvb_device, but I have to admit that I didn't take a close look at that.
> The pads are embedded there, so it is somewhat odd that the entity isn't.
> 
> > 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;
> >> 
> >>  }
> >>  
> >>  /**

-- 
Regards,

Laurent Pinchart