[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, 147 insertions, 0 deletions

diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
new file mode 100644
index 0000000..5c31df9
--- /dev/null
+++ b/drivers/media/media-entity.c
@@ -0,0 +1,147 @@
+/*
+ * Media entity
+ *
+ * Copyright (C) 2010 Nokia Corporation
+ *
+ * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+ *	     Sakari Ailus <sakari.ailus@iki.fi>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <media/media-entity.h>
+
+/**
+ * media_entity_init - Initialize a media entity
+ *
+ * @num_pads: Total number of sink and source pads.
+ * @extra_links: Initial estimate of the number of extra links.
+ * @pads: Array of 'num_pads' pads.
+ *
+ * The total number of pads is an intrinsic property of entities known by the
+ * entity driver, while the total number of links depends on hardware design
+ * and is an extrinsic property unknown to the entity driver. However, in most
+ * use cases the entity driver can guess the number of links which can safely
+ * be assumed to be equal to or larger than the number of pads.
+ *
+ * For those reasons the links array can be preallocated based on the entity
+ * driver guess and will be reallocated later if extra links need to be
+ * created.
+ *
+ * This function allocates a links array with enough space to hold at least
+ * 'num_pads' + 'extra_links' elements. The media_entity::max_links field will
+ * be set to the number of allocated elements.
+ *
+ * The pads array is managed by the entity driver and passed to
+ * media_entity_init() where its pointer will be stored in the entity structure.
+ */
+int
+media_entity_init(struct media_entity *entity, u16 num_pads,
+		  struct media_pad *pads, u16 extra_links)
+{
+	struct media_link *links;
+	unsigned int max_links = num_pads + extra_links;
+	unsigned int i;
+
+	links = kzalloc(max_links * sizeof(links[0]), GFP_KERNEL);
+	if (links == NULL)
+		return -ENOMEM;
+
+	entity->group_id = 0;
+	entity->max_links = max_links;
+	entity->num_links = 0;
+	entity->num_backlinks = 0;
+	entity->num_pads = num_pads;
+	entity->pads = pads;
+	entity->links = links;
+
+	for (i = 0; i < num_pads; i++) {
+		pads[i].entity = entity;
+		pads[i].index = i;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(media_entity_init);
+
+void
+media_entity_cleanup(struct media_entity *entity)
+{
+	kfree(entity->links);
+}
+EXPORT_SYMBOL_GPL(media_entity_cleanup);
+
+static struct media_link *media_entity_add_link(struct media_entity *entity)
+{
+	if (entity->num_links >= entity->max_links) {
+		struct media_link *links = entity->links;
+		unsigned int max_links = entity->max_links + 2;
+		unsigned int i;
+
+		links = krealloc(links, max_links * sizeof(*links), GFP_KERNEL);
+		if (links == NULL)
+			return NULL;
+
+		for (i = 0; i < entity->num_links; i++)
+			links[i].reverse->reverse = &links[i];
+
+		entity->max_links = max_links;
+		entity->links = links;
+	}
+
+	return &entity->links[entity->num_links++];
+}
+
+int
+media_entity_create_link(struct media_entity *source, u16 source_pad,
+			 struct media_entity *sink, u16 sink_pad, u32 flags)
+{
+	struct media_link *link;
+	struct media_link *backlink;
+
+	BUG_ON(source == NULL || sink == NULL);
+	BUG_ON(source_pad >= source->num_pads);
+	BUG_ON(sink_pad >= sink->num_pads);
+
+	link = media_entity_add_link(source);
+	if (link == NULL)
+		return -ENOMEM;
+
+	link->source = &source->pads[source_pad];
+	link->sink = &sink->pads[sink_pad];
+	link->flags = flags;
+
+	/* Create the backlink. Backlinks are used to help graph traversal and
+	 * are not reported to userspace.
+	 */
+	backlink = media_entity_add_link(sink);
+	if (backlink == NULL) {
+		source->num_links--;
+		return -ENOMEM;
+	}
+
+	backlink->source = &source->pads[source_pad];
+	backlink->sink = &sink->pads[sink_pad];
+	backlink->flags = flags;
+
+	link->reverse = backlink;
+	backlink->reverse = link;
+
+	sink->num_backlinks++;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(media_entity_create_link);