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