drivers/media/media-devnode.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Media device node
   4  *
   5  * Copyright (C) 2010 Nokia Corporation
   6  *
   7  * Based on drivers/media/video/v4l2_dev.c code authored by
   8  *      Mauro Carvalho Chehab <mchehab@kernel.org> (version 2)
   9  *      Alan Cox, <alan@lxorguk.ukuu.org.uk> (version 1)
  10  *
  11  * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
  12  *           Sakari Ailus <sakari.ailus@iki.fi>
  13  *
  14  * --
  15  *
  16  * Generic media device node infrastructure to register and unregister
  17  * character devices using a dynamic major number and proper reference
  18  * counting.
  19  */
  20
  21 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  22
  23 #include <linux/errno.h>
  24 #include <linux/init.h>
  25 #include <linux/module.h>
  26 #include <linux/kernel.h>
  27 #include <linux/kmod.h>
  28 #include <linux/slab.h>
  29 #include <linux/mm.h>
  30 #include <linux/string.h>
  31 #include <linux/types.h>
  32 #include <linux/uaccess.h>
  33
  34 #include <media/media-devnode.h>
  35 #include <media/media-device.h>
  36
  37 #define MEDIA_NUM_DEVICES       256
  38 #define MEDIA_NAME              "media"
  39
  40 static dev_t media_dev_t;
  41
  42 /*
  43  *      Active devices
  44  */
  45 static DEFINE_MUTEX(media_devnode_lock);
  46 static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);
  47
  48 /* Called when the last user of the media device exits. */
  49 static void media_devnode_release(struct device *cd)
  50 {
  51         struct media_devnode *devnode = to_media_devnode(cd);
  52
  53         mutex_lock(&media_devnode_lock);
  54         /* Mark device node number as free */
  55         clear_bit(devnode->minor, media_devnode_nums);
  56         mutex_unlock(&media_devnode_lock);
  57
  58         /* Release media_devnode and perform other cleanups as needed. */
  59         if (devnode->release)
  60                 devnode->release(devnode);
  61
  62         kfree(devnode);
  63         pr_debug("%s: Media Devnode Deallocated\n", __func__);
  64 }
  65
  66 static struct bus_type media_bus_type = {
  67         .name = MEDIA_NAME,
  68 };
  69
  70 static ssize_t media_read(struct file *filp, char __user *buf,
  71                 size_t sz, loff_t *off)
  72 {
  73         struct media_devnode *devnode = media_devnode_data(filp);
  74
  75         if (!devnode->fops->read)
  76                 return -EINVAL;
  77         if (!media_devnode_is_registered(devnode))
  78                 return -EIO;
  79         return devnode->fops->read(filp, buf, sz, off);
  80 }
  81
  82 static ssize_t media_write(struct file *filp, const char __user *buf,
  83                 size_t sz, loff_t *off)
  84 {
  85         struct media_devnode *devnode = media_devnode_data(filp);
  86
  87         if (!devnode->fops->write)
  88                 return -EINVAL;
  89         if (!media_devnode_is_registered(devnode))
  90                 return -EIO;
  91         return devnode->fops->write(filp, buf, sz, off);
  92 }
  93
  94 static __poll_t media_poll(struct file *filp,
  95                                struct poll_table_struct *poll)
  96 {
  97         struct media_devnode *devnode = media_devnode_data(filp);
  98
  99         if (!media_devnode_is_registered(devnode))
 100                 return EPOLLERR | EPOLLHUP;
 101         if (!devnode->fops->poll)
 102                 return DEFAULT_POLLMASK;
 103         return devnode->fops->poll(filp, poll);
 104 }
 105
 106 static long
 107 __media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg,
 108               long (*ioctl_func)(struct file *filp, unsigned int cmd,
 109                                  unsigned long arg))
 110 {
 111         struct media_devnode *devnode = media_devnode_data(filp);
 112
 113         if (!ioctl_func)
 114                 return -ENOTTY;
 115
 116         if (!media_devnode_is_registered(devnode))
 117                 return -EIO;
 118
 119         return ioctl_func(filp, cmd, arg);
 120 }
 121
 122 static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 123 {
 124         struct media_devnode *devnode = media_devnode_data(filp);
 125
 126         return __media_ioctl(filp, cmd, arg, devnode->fops->ioctl);
 127 }
 128
 129 #ifdef CONFIG_COMPAT
 130
 131 static long media_compat_ioctl(struct file *filp, unsigned int cmd,
 132                                unsigned long arg)
 133 {
 134         struct media_devnode *devnode = media_devnode_data(filp);
 135
 136         return __media_ioctl(filp, cmd, arg, devnode->fops->compat_ioctl);
 137 }
 138
 139 #endif /* CONFIG_COMPAT */
 140
 141 /* Override for the open function */
 142 static int media_open(struct inode *inode, struct file *filp)
 143 {
 144         struct media_devnode *devnode;
 145         int ret;
 146
 147         /* Check if the media device is available. This needs to be done with
 148          * the media_devnode_lock held to prevent an open/unregister race:
 149          * without the lock, the device could be unregistered and freed between
 150          * the media_devnode_is_registered() and get_device() calls, leading to
 151          * a crash.
 152          */
 153         mutex_lock(&media_devnode_lock);
 154         devnode = container_of(inode->i_cdev, struct media_devnode, cdev);
 155         /* return ENXIO if the media device has been removed
 156            already or if it is not registered anymore. */
 157         if (!media_devnode_is_registered(devnode)) {
 158                 mutex_unlock(&media_devnode_lock);
 159                 return -ENXIO;
 160         }
 161         /* and increase the device refcount */
 162         get_device(&devnode->dev);
 163         mutex_unlock(&media_devnode_lock);
 164
 165         filp->private_data = devnode;
 166
 167         if (devnode->fops->open) {
 168                 ret = devnode->fops->open(filp);
 169                 if (ret) {
 170                         put_device(&devnode->dev);
 171                         filp->private_data = NULL;
 172                         return ret;
 173                 }
 174         }
 175
 176         return 0;
 177 }
 178
 179 /* Override for the release function */
 180 static int media_release(struct inode *inode, struct file *filp)
 181 {
 182         struct media_devnode *devnode = media_devnode_data(filp);
 183
 184         if (devnode->fops->release)
 185                 devnode->fops->release(filp);
 186
 187         filp->private_data = NULL;
 188
 189         /* decrease the refcount unconditionally since the release()
 190            return value is ignored. */
 191         put_device(&devnode->dev);
 192
 193         pr_debug("%s: Media Release\n", __func__);
 194         return 0;
 195 }
 196
 197 static const struct file_operations media_devnode_fops = {
 198         .owner = THIS_MODULE,
 199         .read = media_read,
 200         .write = media_write,
 201         .open = media_open,
 202         .unlocked_ioctl = media_ioctl,
 203 #ifdef CONFIG_COMPAT
 204         .compat_ioctl = media_compat_ioctl,
 205 #endif /* CONFIG_COMPAT */
 206         .release = media_release,
 207         .poll = media_poll,
 208         .llseek = no_llseek,
 209 };
 210
 211 int __must_check media_devnode_register(struct media_device *mdev,
 212                                         struct media_devnode *devnode,
 213                                         struct module *owner)
 214 {
 215         int minor;
 216         int ret;
 217
 218         /* Part 1: Find a free minor number */
 219         mutex_lock(&media_devnode_lock);
 220         minor = find_next_zero_bit(media_devnode_nums, MEDIA_NUM_DEVICES, 0);
 221         if (minor == MEDIA_NUM_DEVICES) {
 222                 mutex_unlock(&media_devnode_lock);
 223                 pr_err("could not get a free minor\n");
 224                 kfree(devnode);
 225                 return -ENFILE;
 226         }
 227
 228         set_bit(minor, media_devnode_nums);
 229         mutex_unlock(&media_devnode_lock);
 230
 231         devnode->minor = minor;
 232         devnode->media_dev = mdev;
 233
 234         /* Part 1: Initialize dev now to use dev.kobj for cdev.kobj.parent */
 235         devnode->dev.bus = &media_bus_type;
 236         devnode->dev.devt = MKDEV(MAJOR(media_dev_t), devnode->minor);
 237         devnode->dev.release = media_devnode_release;
 238         if (devnode->parent)
 239                 devnode->dev.parent = devnode->parent;
 240         dev_set_name(&devnode->dev, "media%d", devnode->minor);
 241         device_initialize(&devnode->dev);
 242
 243         /* Part 2: Initialize the character device */
 244         cdev_init(&devnode->cdev, &media_devnode_fops);
 245         devnode->cdev.owner = owner;
 246         kobject_set_name(&devnode->cdev.kobj, "media%d", devnode->minor);
 247
 248         /* Part 3: Add the media and char device */
 249         ret = cdev_device_add(&devnode->cdev, &devnode->dev);
 250         if (ret < 0) {
 251                 pr_err("%s: cdev_device_add failed\n", __func__);
 252                 goto cdev_add_error;
 253         }
 254
 255         /* Part 4: Activate this minor. The char device can now be used. */
 256         set_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 257
 258         return 0;
 259
 260 cdev_add_error:
 261         mutex_lock(&media_devnode_lock);
 262         clear_bit(devnode->minor, media_devnode_nums);
 263         devnode->media_dev = NULL;
 264         mutex_unlock(&media_devnode_lock);
 265
 266         put_device(&devnode->dev);
 267         return ret;
 268 }
 269
 270 void media_devnode_unregister_prepare(struct media_devnode *devnode)
 271 {
 272         /* Check if devnode was ever registered at all */
 273         if (!media_devnode_is_registered(devnode))
 274                 return;
 275
 276         mutex_lock(&media_devnode_lock);
 277         clear_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
 278         mutex_unlock(&media_devnode_lock);
 279 }
 280
 281 void media_devnode_unregister(struct media_devnode *devnode)
 282 {
 283         mutex_lock(&media_devnode_lock);
 284         /* Delete the cdev on this minor as well */
 285         cdev_device_del(&devnode->cdev, &devnode->dev);
 286         devnode->media_dev = NULL;
 287         mutex_unlock(&media_devnode_lock);
 288
 289         put_device(&devnode->dev);
 290 }
 291
 292 /*
 293  *      Initialise media for linux
 294  */
 295 static int __init media_devnode_init(void)
 296 {
 297         int ret;
 298
 299         pr_info("Linux media interface: v0.10\n");
 300         ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,
 301                                   MEDIA_NAME);
 302         if (ret < 0) {
 303                 pr_warn("unable to allocate major\n");
 304                 return ret;
 305         }
 306
 307         ret = bus_register(&media_bus_type);
 308         if (ret < 0) {
 309                 unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
 310                 pr_warn("bus_register failed\n");
 311                 return -EIO;
 312         }
 313
 314         return 0;
 315 }
 316
 317 static void __exit media_devnode_exit(void)
 318 {
 319         bus_unregister(&media_bus_type);
 320         unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
 321 }
 322
 323 subsys_initcall(media_devnode_init);
 324 module_exit(media_devnode_exit)
 325
 326 MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
 327 MODULE_DESCRIPTION("Device node registration for media drivers");
 328 MODULE_LICENSE("GPL");