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