[media] media: Entities, pads and links

As video hardware pipelines become increasingly complex and
configurable, the current hardware description through v4l2 subdevices
reaches its limits. In addition to enumerating and configuring
subdevices, video camera drivers need a way to discover and modify at
runtime how those subdevices are connected. This is done through new
elements called entities, pads and links.

An entity is a basic media hardware building block. It can correspond to
a large variety of logical blocks such as physical hardware devices
(CMOS sensor for instance), logical hardware devices (a building block
in a System-on-Chip image processing pipeline), DMA channels or physical
connectors.

A pad is a connection endpoint through which an entity can interact with
other entities. Data (not restricted to video) produced by an entity
flows from the entity's output to one or more entity inputs. Pads should
not be confused with physical pins at chip boundaries.

A link is a point-to-point oriented connection between two pads, either
on the same entity or on different entities. Data flows from a source
pad to a sink pad.

Links are stored in the source entity. To make backwards graph walk
faster, a copy of all links is also stored in the sink entity. The copy
is known as a backlink and is only used to help graph traversal.

The entity API is made of three functions:

- media_entity_init() initializes an entity. The caller must provide an
array of pads as well as an estimated number of links. The links array
is allocated dynamically and will be reallocated if it grows beyond the
initial estimate.

- media_entity_cleanup() frees resources allocated for an entity. It
must be called during the cleanup phase after unregistering the entity
and before freeing it.

- media_entity_create_link() creates a link between two entities. An
entry in the link array of each entity is allocated and stores pointers
to source and sink pads.

When a media device is unregistered, all its entities are unregistered
automatically.

The code is based on Hans Verkuil <hverkuil@xs4all.nl> initial work.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/include/media/media-device.h b/include/media/media-device.h
index 30857f7..a8390fe 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -25,8 +25,10 @@
 
 #include <linux/device.h>
 #include <linux/list.h>
+#include <linux/spinlock.h>
 
 #include <media/media-devnode.h>
+#include <media/media-entity.h>
 
 /**
  * struct media_device - Media device
@@ -37,6 +39,9 @@
  * @bus_info:	Unique and stable device location identifier
  * @hw_revision: Hardware device revision
  * @driver_version: Device driver version
+ * @entity_id:	ID of the next entity to be registered
+ * @entities:	List of registered entities
+ * @lock:	Entities list lock
  *
  * This structure represents an abstract high-level media device. It allows easy
  * access to entities and provides basic media device-level support. The
@@ -58,6 +63,12 @@ struct media_device {
 	char bus_info[32];
 	u32 hw_revision;
 	u32 driver_version;
+
+	u32 entity_id;
+	struct list_head entities;
+
+	/* Protects the entities list */
+	spinlock_t lock;
 };
 
 /* media_devnode to media_device */
@@ -66,4 +77,12 @@ struct media_device {
 int __must_check media_device_register(struct media_device *mdev);
 void media_device_unregister(struct media_device *mdev);
 
+int __must_check media_device_register_entity(struct media_device *mdev,
+					      struct media_entity *entity);
+void media_device_unregister_entity(struct media_entity *entity);
+
+/* Iterate over all entities. */
+#define media_device_for_each_entity(entity, mdev)			\
+	list_for_each_entry(entity, &(mdev)->entities, list)
+
 #endif