Message-Id: <1292844995-7900-3-git-send-email-laurent.pinchart@ideasonboard.com>
Date:	Mon, 20 Dec 2010 12:36:25 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org
Cc:	broonie@...nsource.wolfsonmicro.com, clemens@...isch.de,
	gregkh@...e.de, sakari.ailus@...well.research.nokia.com
Subject: [RFC/PATCH v7 02/12] media: Media device

The media_device structure abstracts functions common to all kind of
media devices (v4l2, dvb, alsa, ...). It manages media entities and
offers a userspace API to discover and configure the media device
internal topology.

Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
---
 Documentation/DocBook/media-entities.tmpl      |    2 +
 Documentation/DocBook/media.tmpl               |    3 +
 Documentation/DocBook/v4l/media-controller.xml |   56 +++++++++++++
 Documentation/media-framework.txt              |   68 ++++++++++++++++
 drivers/media/Makefile                         |    2 +-
 drivers/media/media-device.c                   |  100 ++++++++++++++++++++++++
 include/media/media-device.h                   |   69 ++++++++++++++++
 7 files changed, 299 insertions(+), 1 deletions(-)
 create mode 100644 Documentation/DocBook/v4l/media-controller.xml
 create mode 100644 Documentation/media-framework.txt
 create mode 100644 drivers/media/media-device.c
 create mode 100644 include/media/media-device.h

diff --git a/Documentation/DocBook/media-entities.tmpl b/Documentation/DocBook/media-entities.tmpl
index be34dcb..61d6f11 100644
--- a/Documentation/DocBook/media-entities.tmpl
+++ b/Documentation/DocBook/media-entities.tmpl
@@ -321,6 +321,8 @@
 <!ENTITY sub-media-entities SYSTEM "media-entities.tmpl">
 <!ENTITY sub-media-indices SYSTEM "media-indices.tmpl">
 
+<!ENTITY sub-media-controller SYSTEM "v4l/media-controller.xml">
+
 <!-- Function Reference -->
 <!ENTITY close SYSTEM "v4l/func-close.xml">
 <!ENTITY ioctl SYSTEM "v4l/func-ioctl.xml">
diff --git a/Documentation/DocBook/media.tmpl b/Documentation/DocBook/media.tmpl
index f11048d..73464b0 100644
--- a/Documentation/DocBook/media.tmpl
+++ b/Documentation/DocBook/media.tmpl
@@ -106,6 +106,9 @@ Foundation. A copy of the license is included in the chapter entitled
 &sub-remote_controllers;
 </chapter>
 </part>
+<part id="media_common">
+&sub-media-controller;
+</part>
 
 &sub-fdl-appendix;
 
diff --git a/Documentation/DocBook/v4l/media-controller.xml b/Documentation/DocBook/v4l/media-controller.xml
new file mode 100644
index 0000000..253ddb4
--- /dev/null
+++ b/Documentation/DocBook/v4l/media-controller.xml
@@ -0,0 +1,56 @@
+<partinfo>
+  <authorgroup>
+    <author>
+      <firstname>Laurent</firstname>
+      <surname>Pinchart</surname>
+      <affiliation><address><email>laurent.pinchart@...asonboard.com</email></address></affiliation>
+      <contrib>Initial version.</contrib>
+    </author>
+  </authorgroup>
+  <copyright>
+    <year>2010</year>
+    <holder>Laurent Pinchart</holder>
+  </copyright>
+
+  <revhistory>
+    <!-- Put document revisions here, newest first. -->
+    <revision>
+      <revnumber>1.0.0</revnumber>
+      <date>2010-11-10</date>
+      <authorinitials>lp</authorinitials>
+      <revremark>Initial revision</revremark>
+    </revision>
+  </revhistory>
+</partinfo>
+
+<title>Media Controller API</title>
+
+<chapter id="media_controller">
+  <title>Media Controller</title>
+
+  <section id="media-controller-intro">
+    <title>Introduction</title>
+    <para>Media devices increasingly handle multiple related functions. Many USB
+    cameras include microphones, video capture hardware can also output video,
+    or SoC camera interfaces also perform memory-to-memory operations similar to
+    video codecs.</para>
+    <para>Independent functions, even when implemented in the same hardware, can
+    be modelled as separate devices. A USB camera with a microphone will be
+    presented to userspace applications as V4L2 and ALSA capture devices. The
+    devices' relationships (when using a webcam, end-users shouldn't have to
+    manually select the associated USB microphone), while not made available
+    directly to applications by the drivers, can usually be retrieved from
+    sysfs.</para>
+    <para>With more and more advanced SoC devices being introduced, the current
+    approach will not scale. Device topologies are getting increasingly complex
+    and can't always be represented by a tree structure. Hardware blocks are
+    shared between different functions, creating dependencies between seemingly
+    unrelated devices.</para>
+    <para>Kernel abstraction APIs such as V4L2 and ALSA provide means for
+    applications to access hardware parameters. As newer hardware expose an
+    increasingly high number of those parameters, drivers need to guess what
+    applications really require based on limited information, thereby
+    implementing policies that belong to userspace.</para>
+    <para>The media controller API aims at solving those problems.</para>
+  </section>
+</chapter>
diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt
new file mode 100644
index 0000000..84fa43a
--- /dev/null
+++ b/Documentation/media-framework.txt
@@ -0,0 +1,68 @@
+Linux kernel media framework
+============================
+
+This document describes the Linux kernel media framework, its data structures,
+functions and their usage.
+
+
+Introduction
+------------
+
+The media controller API is documented in DocBook format in
+Documentation/DocBook/v4l/media-controller.xml. This document will focus on
+the kernel-side implementation of the media framework.
+
+
+Media device
+------------
+
+A media device is represented by a struct media_device instance, defined in
+include/media/media-device.h. Allocation of the structure is handled by the
+media device driver, usually by embedding the media_device instance in a
+larger driver-specific structure.
+
+Drivers register media device instances by calling
+
+	media_device_register(struct media_device *mdev);
+
+The caller is responsible for initializing the media_device structure before
+registration. The following fields must be set:
+
+ - dev must point to the parent device (usually a pci_dev, usb_interface or
+   platform_device instance).
+
+ - model must be filled with the device model name as a NUL-terminated UTF-8
+   string. The device/model revision must not be stored in this field.
+
+The following fields are optional:
+
+ - serial is a unique serial number stored as a NUL-terminated ASCII string.
+   The field is big enough to store a GUID in text form. If the hardware
+   doesn't provide a unique serial number this field must be left empty.
+
+ - bus_info represents the location of the device in the system as a
+   NUL-terminated ASCII string. For PCI/PCIe devices bus_info must be set to
+   "PCI:" (or "PCIe:") followed by the value of pci_name(). For USB devices,
+   the usb_make_path() function must be used. This field is used by
+   applications to distinguish between otherwise identical devices that don't
+   provide a serial number.
+
+ - hw_revision is the hardware device revision in a driver-specific format.
+   When possible the revision should be formatted with the KERNEL_VERSION
+   macro.
+
+ - driver_version is formatted with the KERNEL_VERSION macro. The version
+   minor must be incremented when new features are added to the userspace API
+   without breaking binary compatibility. The version major must be
+   incremented when binary compatibility is broken.
+
+Upon successful registration a character device named media[0-9]+ is created.
+The device major and minor numbers are dynamic. The model name is exported as
+a sysfs attribute.
+
+Drivers unregister media device instances by calling
+
+	media_device_unregister(struct media_device *mdev);
+
+Unregistering a media device that hasn't been registered is *NOT* safe.
+
diff --git a/drivers/media/Makefile b/drivers/media/Makefile
index 3a08991..019d3e0 100644
--- a/drivers/media/Makefile
+++ b/drivers/media/Makefile
@@ -2,7 +2,7 @@
 # Makefile for the kernel multimedia device drivers.
 #
 
-media-objs	:= media-devnode.o
+media-objs	:= media-device.o media-devnode.o
 
 ifeq ($(CONFIG_MEDIA_CONTROLLER),y)
   obj-$(CONFIG_MEDIA_SUPPORT) += media.o
diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
new file mode 100644
index 0000000..57a9c6b
--- /dev/null
+++ b/drivers/media/media-device.c
@@ -0,0 +1,100 @@
+/*
+ * Media device
+ *
+ * Copyright (C) 2010 Nokia Corporation
+ *
+ * Contacts: Laurent Pinchart <laurent.pinchart@...asonboard.com>
+ *	     Sakari Ailus <sakari.ailus@...well.research.nokia.com>
+ *
+ * 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/types.h>
+#include <linux/ioctl.h>
+
+#include <media/media-device.h>
+#include <media/media-devnode.h>
+
+static const struct media_file_operations media_device_fops = {
+	.owner = THIS_MODULE,
+};
+
+/* -----------------------------------------------------------------------------
+ * sysfs
+ */
+
+static ssize_t show_model(struct device *cd,
+			  struct device_attribute *attr, char *buf)
+{
+	struct media_device *mdev = to_media_device(to_media_devnode(cd));
+
+	return sprintf(buf, "%.*s\n", (int)sizeof(mdev->model), mdev->model);
+}
+
+static DEVICE_ATTR(model, S_IRUGO, show_model, NULL);
+
+/* -----------------------------------------------------------------------------
+ * Registration/unregistration
+ */
+
+static void media_device_release(struct media_devnode *mdev)
+{
+}
+
+/**
+ * media_device_register - register a media device
+ * @mdev:	The media device
+ *
+ * The caller is responsible for initializing the media device before
+ * registration. The following fields must be set:
+ *
+ * - dev must point to the parent device
+ * - model must be filled with the device model name
+ */
+int __must_check media_device_register(struct media_device *mdev)
+{
+	int ret;
+
+	if (WARN_ON(mdev->dev == NULL || mdev->model[0] == 0))
+		return -EINVAL;
+
+	/* Register the device node. */
+	mdev->devnode.fops = &media_device_fops;
+	mdev->devnode.parent = mdev->dev;
+	mdev->devnode.release = media_device_release;
+	ret = media_devnode_register(&mdev->devnode);
+	if (ret < 0)
+		return ret;
+
+	ret = device_create_file(&mdev->devnode.dev, &dev_attr_model);
+	if (ret < 0) {
+		media_devnode_unregister(&mdev->devnode);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(media_device_register);
+
+/**
+ * media_device_unregister - unregister a media device
+ * @mdev:	The media device
+ *
+ */
+void media_device_unregister(struct media_device *mdev)
+{
+	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
+	media_devnode_unregister(&mdev->devnode);
+}
+EXPORT_SYMBOL_GPL(media_device_unregister);
diff --git a/include/media/media-device.h b/include/media/media-device.h
new file mode 100644
index 0000000..e11f01a
--- /dev/null
+++ b/include/media/media-device.h
@@ -0,0 +1,69 @@
+/*
+ * Media device
+ *
+ * Copyright (C) 2010 Nokia Corporation
+ *
+ * Contacts: Laurent Pinchart <laurent.pinchart@...asonboard.com>
+ *	     Sakari Ailus <sakari.ailus@...well.research.nokia.com>
+ *
+ * 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
+ */
+
+#ifndef _MEDIA_DEVICE_H
+#define _MEDIA_DEVICE_H
+
+#include <linux/device.h>
+#include <linux/list.h>
+
+#include <media/media-devnode.h>
+
+/**
+ * struct media_device - Media device
+ * @dev:	Parent device
+ * @devnode:	Media device node
+ * @model:	Device model name
+ * @serial:	Device serial number (optional)
+ * @bus_info:	Unique and stable device location identifier
+ * @hw_revision: Hardware device revision
+ * @driver_version: Device driver version
+ *
+ * This structure represents an abstract high-level media device. It allows easy
+ * access to entities and provides basic media device-level support. The
+ * structure can be allocated directly or embedded in a larger structure.
+ *
+ * The parent @dev is a physical device. It must be set before registering the
+ * media device.
+ *
+ * @model is a descriptive model name exported through sysfs. It doesn't have to
+ * be unique.
+ */
+struct media_device {
+	/* dev->driver_data points to this struct. */
+	struct device *dev;
+	struct media_devnode devnode;
+
+	char model[32];
+	char serial[40];
+	char bus_info[32];
+	u32 hw_revision;
+	u32 driver_version;
+};
+
+/* media_devnode to media_device */
+#define to_media_device(node) container_of(node, struct media_device, devnode)
+
+int __must_check media_device_register(struct media_device *mdev);
+void media_device_unregister(struct media_device *mdev);
+
+#endif
-- 
1.7.2.2

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