drivers/media/media-devnode.c

   1 /*
   2  * Media device node
   3  *
   4  * Copyright (C) 2010 Nokia Corporation
   5  *
   6  * Based on drivers/media/video/v4l2_dev.c code authored by
   7  *      Mauro Carvalho Chehab <mchehab@infradead.org> (version 2)
   8  *      Alan Cox, <alan@lxorguk.ukuu.org.uk> (version 1)
   9  *
  10  * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
  11  *           Sakari Ailus <sakari.ailus@iki.fi>
  12  *
  13  * This program is free software; you can redistribute it and/or modify
  14  * it under the terms of the GNU General Public License version 2 as
  15  * published by the Free Software Foundation.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  25  *
  26  * --
  27  *
  28  * Generic media device node infrastructure to register and unregister
  29  * character devices using a dynamic major number and proper reference
  30  * counting.
  31  */
  32
  33 #include <linux/errno.h>
  34 #include <linux/init.h>
  35 #include <linux/module.h>
  36 #include <linux/kernel.h>
  37 #include <linux/kmod.h>
  38 #include <linux/slab.h>
  39 #include <linux/mm.h>
  40 #include <linux/string.h>
  41 #include <linux/types.h>
  42 #include <linux/uaccess.h>
  43
  44 #include <media/media-devnode.h>
  45
  46 #define MEDIA_NUM_DEVICES       256
  47 #define MEDIA_NAME              "media"
  48
  49 static dev_t media_dev_t;
  50
  51 /*
  52  *      Active devices
  53  */
  54 static DEFINE_MUTEX(media_devnode_lock);
  55 static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);
  56
  57 /* Called when the last user of the media device exits. */
  58 static void media_devnode_release(struct device *cd)
  59 {
  60         struct media_devnode *mdev = to_media_devnode(cd);
  61
  62         mutex_lock(&media_devnode_lock);
  63
  64         /* Delete the cdev on this minor as well */
  65         cdev_del(&mdev->cdev);
  66
  67         /* Mark device node number as free */
  68         clear_bit(mdev->minor, media_devnode_nums);
  69
  70         mutex_unlock(&media_devnode_lock);
  71
  72         /* Release media_devnode and perform other cleanups as needed. */
  73         if (mdev->release)
  74                 mdev->release(mdev);
  75 }
  76
  77 static struct bus_type media_bus_type = {
  78         .name = MEDIA_NAME,
  79 };
  80
  81 static ssize_t media_read(struct file *filp, char __user *buf,
  82                 size_t sz, loff_t *off)
  83 {
  84         struct media_devnode *mdev = media_devnode_data(filp);
  85
  86         if (!mdev->fops->read)
  87                 return -EINVAL;
  88         if (!media_devnode_is_registered(mdev))
  89                 return -EIO;
  90         return mdev->fops->read(filp, buf, sz, off);
  91 }
  92
  93 static ssize_t media_write(struct file *filp, const char __user *buf,
  94                 size_t sz, loff_t *off)
  95 {
  96         struct media_devnode *mdev = media_devnode_data(filp);
  97
  98         if (!mdev->fops->write)
  99                 return -EINVAL;
 100         if (!media_devnode_is_registered(mdev))
 101                 return -EIO;
 102         return mdev->fops->write(filp, buf, sz, off);
 103 }
 104
 105 static unsigned int media_poll(struct file *filp,
 106                                struct poll_table_struct *poll)
 107 {
 108         struct media_devnode *mdev = media_devnode_data(filp);
 109
 110         if (!media_devnode_is_registered(mdev))
 111                 return POLLERR | POLLHUP;
 112         if (!mdev->fops->poll)
 113                 return DEFAULT_POLLMASK;
 114         return mdev->fops->poll(filp, poll);
 115 }
 116
 117 static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 118 {
 119         struct media_devnode *mdev = media_devnode_data(filp);
 120
 121         if (!mdev->fops->ioctl)
 122                 return -ENOTTY;
 123
 124         if (!media_devnode_is_registered(mdev))
 125                 return -EIO;
 126
 127         return mdev->fops->ioctl(filp, cmd, arg);
 128 }
 129
 130 /* Override for the open function */
 131 static int media_open(struct inode *inode, struct file *filp)
 132 {
 133         struct media_devnode *mdev;
 134         int ret;
 135
 136         /* Check if the media device is available. This needs to be done with
 137          * the media_devnode_lock held to prevent an open/unregister race:
 138          * without the lock, the device could be unregistered and freed between
 139          * the media_devnode_is_registered() and get_device() calls, leading to
 140          * a crash.
 141          */
 142         mutex_lock(&media_devnode_lock);
 143         mdev = container_of(inode->i_cdev, struct media_devnode, cdev);
 144         /* return ENXIO if the media device has been removed
 145            already or if it is not registered anymore. */
 146         if (!media_devnode_is_registered(mdev)) {
 147                 mutex_unlock(&media_devnode_lock);
 148                 return -ENXIO;
 149         }
 150         /* and increase the device refcount */
 151         get_device(&mdev->dev);
 152         mutex_unlock(&media_devnode_lock);
 153
 154         filp->private_data = mdev;
 155
 156         if (mdev->fops->open) {
 157                 ret = mdev->fops->open(filp);
 158                 if (ret) {
 159                         put_device(&mdev->dev);
 160                         return ret;
 161                 }
 162         }
 163
 164         return 0;
 165 }
 166
 167 /* Override for the release function */
 168 static int media_release(struct inode *inode, struct file *filp)
 169 {
 170         struct media_devnode *mdev = media_devnode_data(filp);
 171         int ret = 0;
 172
 173         if (mdev->fops->release)
 174                 mdev->fops->release(filp);
 175
 176         /* decrease the refcount unconditionally since the release()
 177            return value is ignored. */
 178         put_device(&mdev->dev);
 179         filp->private_data = NULL;
 180         return ret;
 181 }
 182
 183 static const struct file_operations media_devnode_fops = {
 184         .owner = THIS_MODULE,
 185         .read = media_read,
 186         .write = media_write,
 187         .open = media_open,
 188         .unlocked_ioctl = media_ioctl,
 189         .release = media_release,
 190         .poll = media_poll,
 191         .llseek = no_llseek,
 192 };
 193
 194 /**
 195  * media_devnode_register - register a media device node
 196  * @mdev: media device node structure we want to register
 197  *
 198  * The registration code assigns minor numbers and registers the new device node
 199  * with the kernel. An error is returned if no free minor number can be found,
 200  * or if the registration of the device node fails.
 201  *
 202  * Zero is returned on success.
 203  *
 204  * Note that if the media_devnode_register call fails, the release() callback of
 205  * the media_devnode structure is *not* called, so the caller is responsible for
 206  * freeing any data.
 207  */
 208 int __must_check media_devnode_register(struct media_devnode *mdev)
 209 {
 210         int minor;
 211         int ret;
 212
 213         /* Part 1: Find a free minor number */
 214         mutex_lock(&media_devnode_lock);
 215         minor = find_next_zero_bit(media_devnode_nums, MEDIA_NUM_DEVICES, 0);
 216         if (minor == MEDIA_NUM_DEVICES) {
 217                 mutex_unlock(&media_devnode_lock);
 218                 printk(KERN_ERR "could not get a free minor\n");
 219                 return -ENFILE;
 220         }
 221
 222         set_bit(minor, media_devnode_nums);
 223         mutex_unlock(&media_devnode_lock);
 224
 225         mdev->minor = minor;
 226
 227         /* Part 2: Initialize and register the character device */
 228         cdev_init(&mdev->cdev, &media_devnode_fops);
 229         mdev->cdev.owner = mdev->fops->owner;
 230
 231         ret = cdev_add(&mdev->cdev, MKDEV(MAJOR(media_dev_t), mdev->minor), 1);
 232         if (ret < 0) {
 233                 printk(KERN_ERR "%s: cdev_add failed\n", __func__);
 234                 goto error;
 235         }
 236
 237         /* Part 3: Register the media device */
 238         mdev->dev.bus = &media_bus_type;
 239         mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);
 240         mdev->dev.release = media_devnode_release;
 241         if (mdev->parent)
 242                 mdev->dev.parent = mdev->parent;
 243         dev_set_name(&mdev->dev, "media%d", mdev->minor);
 244         ret = device_register(&mdev->dev);
 245         if (ret < 0) {
 246                 printk(KERN_ERR "%s: device_register failed\n", __func__);
 247                 goto error;
 248         }
 249
 250         /* Part 4: Activate this minor. The char device can now be used. */
 251         set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
 252
 253         return 0;
 254
 255 error:
 256         cdev_del(&mdev->cdev);
 257         clear_bit(mdev->minor, media_devnode_nums);
 258         return ret;
 259 }
 260
 261 /**
 262  * media_devnode_unregister - unregister a media device node
 263  * @mdev: the device node to unregister
 264  *
 265  * This unregisters the passed device. Future open calls will be met with
 266  * errors.
 267  *
 268  * This function can safely be called if the device node has never been
 269  * registered or has already been unregistered.
 270  */
 271 void media_devnode_unregister(struct media_devnode *mdev)
 272 {
 273         /* Check if mdev was ever registered at all */
 274         if (!media_devnode_is_registered(mdev))
 275                 return;
 276
 277         mutex_lock(&media_devnode_lock);
 278         clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
 279         mutex_unlock(&media_devnode_lock);
 280         device_unregister(&mdev->dev);
 281 }
 282
 283 /*
 284  *      Initialise media for linux
 285  */
 286 static int __init media_devnode_init(void)
 287 {
 288         int ret;
 289
 290         printk(KERN_INFO "Linux media interface: v0.10\n");
 291         ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,
 292                                   MEDIA_NAME);
 293         if (ret < 0) {
 294                 printk(KERN_WARNING "media: unable to allocate major\n");
 295                 return ret;
 296         }
 297
 298         ret = bus_register(&media_bus_type);
 299         if (ret < 0) {
 300                 unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
 301                 printk(KERN_WARNING "media: bus_register failed\n");
 302                 return -EIO;
 303         }
 304
 305         return 0;
 306 }
 307
 308 static void __exit media_devnode_exit(void)
 309 {
 310         bus_unregister(&media_bus_type);
 311         unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
 312 }
 313
 314 subsys_initcall(media_devnode_init);
 315 module_exit(media_devnode_exit)
 316
 317 MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
 318 MODULE_DESCRIPTION("Device node registration for media drivers");
 319 MODULE_LICENSE("GPL");