[media] media: Media device node support

The media_devnode structure provides support for registering and
unregistering character devices using a dynamic major number. Reference
counting is handled internally, making device drivers easier to write
without having to solve the open/disconnect race condition issue over
and over again.

The code is based on video/v4l2-dev.c.

[mchehab@redhat.com: Remove linux/smp_lock.h include to not break compilation on bisect]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

3 files changed, 339 insertions, 0 deletions

diff --git a/drivers/media/Kconfig b/drivers/media/Kconfig
index 81b3ba83cc65..2466f2b2ecfa 100644
--- a/drivers/media/Kconfig
+++ b/drivers/media/Kconfig
@@ -14,6 +14,19 @@ if MEDIA_SUPPORT
 comment "Multimedia core support"
 
 #
+# Media controller
+#
+
+config MEDIA_CONTROLLER
+        bool "Media Controller API (EXPERIMENTAL)"
+        depends on EXPERIMENTAL
+        ---help---
+          Enable the media controller API used to query media devices internal
+          topology and configure it dynamically.
+
+          This API is mostly used by camera interfaces in embedded platforms.
+
+#
 # V4L core and enabled API's
 #
 
diff --git a/drivers/media/Makefile b/drivers/media/Makefile
index b603ea645ede..d56349f6103f 100644
--- a/drivers/media/Makefile
+++ b/drivers/media/Makefile
@@ -2,6 +2,12 @@
 # Makefile for the kernel multimedia device drivers.
 #
 
+media-objs      := media-devnode.o
+
+ifeq ($(CONFIG_MEDIA_CONTROLLER),y)
+  obj-$(CONFIG_MEDIA_SUPPORT) += media.o
+endif
+
 obj-y += common/ rc/ video/
 
 obj-$(CONFIG_VIDEO_DEV) += radio/
diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c
new file mode 100644
index 000000000000..af5263c6625a
--- /dev/null
+++ b/drivers/media/media-devnode.c
@@ -0,0 +1,320 @@
+/*
+ * Media device node
+ *
+ * Copyright (C) 2010 Nokia Corporation
+ *
+ * Based on drivers/media/video/v4l2_dev.c code authored by
+ *      Mauro Carvalho Chehab <mchehab@infradead.org> (version 2)
+ *      Alan Cox, <alan@lxorguk.ukuu.org.uk> (version 1)
+ *
+ * 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
+ *
+ * --
+ *
+ * Generic media device node infrastructure to register and unregister
+ * character devices using a dynamic major number and proper reference
+ * counting.
+ */
+
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/kmod.h>
+#include <linux/slab.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+#include <asm/system.h>
+
+#include <media/media-devnode.h>
+
+#define MEDIA_NUM_DEVICES       256
+#define MEDIA_NAME              "media"
+
+static dev_t media_dev_t;
+
+/*
+ *      Active devices
+ */
+static DEFINE_MUTEX(media_devnode_lock);
+static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);
+
+/* Called when the last user of the media device exits. */
+static void media_devnode_release(struct device *cd)
+{
+        struct media_devnode *mdev = to_media_devnode(cd);
+
+        mutex_lock(&media_devnode_lock);
+
+        /* Delete the cdev on this minor as well */
+        cdev_del(&mdev->cdev);
+
+        /* Mark device node number as free */
+        clear_bit(mdev->minor, media_devnode_nums);
+
+        mutex_unlock(&media_devnode_lock);
+
+        /* Release media_devnode and perform other cleanups as needed. */
+        if (mdev->release)
+                mdev->release(mdev);
+}
+
+static struct bus_type media_bus_type = {
+        .name = MEDIA_NAME,
+};
+
+static ssize_t media_read(struct file *filp, char __user *buf,
+                size_t sz, loff_t *off)
+{
+        struct media_devnode *mdev = media_devnode_data(filp);
+
+        if (!mdev->fops->read)
+                return -EINVAL;
+        if (!media_devnode_is_registered(mdev))
+                return -EIO;
+        return mdev->fops->read(filp, buf, sz, off);
+}
+
+static ssize_t media_write(struct file *filp, const char __user *buf,
+                size_t sz, loff_t *off)
+{
+        struct media_devnode *mdev = media_devnode_data(filp);
+
+        if (!mdev->fops->write)
+                return -EINVAL;
+        if (!media_devnode_is_registered(mdev))
+                return -EIO;
+        return mdev->fops->write(filp, buf, sz, off);
+}
+
+static unsigned int media_poll(struct file *filp,
+                               struct poll_table_struct *poll)
+{
+        struct media_devnode *mdev = media_devnode_data(filp);
+
+        if (!media_devnode_is_registered(mdev))
+                return POLLERR | POLLHUP;
+        if (!mdev->fops->poll)
+                return DEFAULT_POLLMASK;
+        return mdev->fops->poll(filp, poll);
+}
+
+static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+        struct media_devnode *mdev = media_devnode_data(filp);
+
+        if (!mdev->fops->ioctl)
+                return -ENOTTY;
+
+        if (!media_devnode_is_registered(mdev))
+                return -EIO;
+
+        return mdev->fops->ioctl(filp, cmd, arg);
+}
+
+/* Override for the open function */
+static int media_open(struct inode *inode, struct file *filp)
+{
+        struct media_devnode *mdev;
+        int ret;
+
+        /* Check if the media device is available. This needs to be done with
+         * the media_devnode_lock held to prevent an open/unregister race:
+         * without the lock, the device could be unregistered and freed between
+         * the media_devnode_is_registered() and get_device() calls, leading to
+         * a crash.
+         */
+        mutex_lock(&media_devnode_lock);
+        mdev = container_of(inode->i_cdev, struct media_devnode, cdev);
+        /* return ENXIO if the media device has been removed
+           already or if it is not registered anymore. */
+        if (!media_devnode_is_registered(mdev)) {
+                mutex_unlock(&media_devnode_lock);
+                return -ENXIO;
+        }
+        /* and increase the device refcount */
+        get_device(&mdev->dev);
+        mutex_unlock(&media_devnode_lock);
+
+        filp->private_data = mdev;
+
+        if (mdev->fops->open) {
+                ret = mdev->fops->open(filp);
+                if (ret) {
+                        put_device(&mdev->dev);
+                        return ret;
+                }
+        }
+
+        return 0;
+}
+
+/* Override for the release function */
+static int media_release(struct inode *inode, struct file *filp)
+{
+        struct media_devnode *mdev = media_devnode_data(filp);
+        int ret = 0;
+
+        if (mdev->fops->release)
+                mdev->fops->release(filp);
+
+        /* decrease the refcount unconditionally since the release()
+           return value is ignored. */
+        put_device(&mdev->dev);
+        filp->private_data = NULL;
+        return ret;
+}
+
+static const struct file_operations media_devnode_fops = {
+        .owner = THIS_MODULE,
+        .read = media_read,
+        .write = media_write,
+        .open = media_open,
+        .unlocked_ioctl = media_ioctl,
+        .release = media_release,
+        .poll = media_poll,
+        .llseek = no_llseek,
+};
+
+/**
+ * media_devnode_register - register a media device node
+ * @mdev: media device node structure we want to register
+ *
+ * The registration code assigns minor numbers and registers the new device node
+ * with the kernel. An error is returned if no free minor number can be found,
+ * or if the registration of the device node fails.
+ *
+ * Zero is returned on success.
+ *
+ * Note that if the media_devnode_register call fails, the release() callback of
+ * the media_devnode structure is *not* called, so the caller is responsible for
+ * freeing any data.
+ */
+int __must_check media_devnode_register(struct media_devnode *mdev)
+{
+        int minor;
+        int ret;
+
+        /* Part 1: Find a free minor number */
+        mutex_lock(&media_devnode_lock);
+        minor = find_next_zero_bit(media_devnode_nums, 0, MEDIA_NUM_DEVICES);
+        if (minor == MEDIA_NUM_DEVICES) {
+                mutex_unlock(&media_devnode_lock);
+                printk(KERN_ERR "could not get a free minor\n");
+                return -ENFILE;
+        }
+
+        set_bit(mdev->minor, media_devnode_nums);
+        mutex_unlock(&media_devnode_lock);
+
+        mdev->minor = minor;
+
+        /* Part 2: Initialize and register the character device */
+        cdev_init(&mdev->cdev, &media_devnode_fops);
+        mdev->cdev.owner = mdev->fops->owner;
+
+        ret = cdev_add(&mdev->cdev, MKDEV(MAJOR(media_dev_t), mdev->minor), 1);
+        if (ret < 0) {
+                printk(KERN_ERR "%s: cdev_add failed\n", __func__);
+                goto error;
+        }
+
+        /* Part 3: Register the media device */
+        mdev->dev.bus = &media_bus_type;
+        mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);
+        mdev->dev.release = media_devnode_release;
+        if (mdev->parent)
+                mdev->dev.parent = mdev->parent;
+        dev_set_name(&mdev->dev, "media%d", mdev->minor);
+        ret = device_register(&mdev->dev);
+        if (ret < 0) {
+                printk(KERN_ERR "%s: device_register failed\n", __func__);
+                goto error;
+        }
+
+        /* Part 4: Activate this minor. The char device can now be used. */
+        set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
+
+        return 0;
+
+error:
+        cdev_del(&mdev->cdev);
+        clear_bit(mdev->minor, media_devnode_nums);
+        return ret;
+}
+
+/**
+ * media_devnode_unregister - unregister a media device node
+ * @mdev: the device node to unregister
+ *
+ * This unregisters the passed device. Future open calls will be met with
+ * errors.
+ *
+ * This function can safely be called if the device node has never been
+ * registered or has already been unregistered.
+ */
+void media_devnode_unregister(struct media_devnode *mdev)
+{
+        /* Check if mdev was ever registered at all */
+        if (!media_devnode_is_registered(mdev))
+                return;
+
+        mutex_lock(&media_devnode_lock);
+        clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
+        mutex_unlock(&media_devnode_lock);
+        device_unregister(&mdev->dev);
+}
+
+/*
+ *      Initialise media for linux
+ */
+static int __init media_devnode_init(void)
+{
+        int ret;
+
+        printk(KERN_INFO "Linux media interface: v0.10\n");
+        ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,
+                                  MEDIA_NAME);
+        if (ret < 0) {
+                printk(KERN_WARNING "media: unable to allocate major\n");
+                return ret;
+        }
+
+        ret = bus_register(&media_bus_type);
+        if (ret < 0) {
+                unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
+                printk(KERN_WARNING "media: bus_register failed\n");
+                return -EIO;
+        }
+
+        return 0;
+}
+
+static void __exit media_devnode_exit(void)
+{
+        bus_unregister(&media_bus_type);
+        unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
+}
+
+module_init(media_devnode_init)
+module_exit(media_devnode_exit)
+
+MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
+MODULE_DESCRIPTION("Device node registration for media drivers");
+MODULE_LICENSE("GPL");