drivers/base/firmware_loader/fallback.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include <linux/types.h>
   4 #include <linux/kconfig.h>
   5 #include <linux/list.h>
   6 #include <linux/slab.h>
   7 #include <linux/security.h>
   8 #include <linux/highmem.h>
   9 #include <linux/umh.h>
  10 #include <linux/sysctl.h>
  11 #include <linux/vmalloc.h>
  12
  13 #include "fallback.h"
  14 #include "firmware.h"
  15
  16 /*
  17  * firmware fallback mechanism
  18  */
  19
  20 extern struct firmware_fallback_config fw_fallback_config;
  21
  22 /* These getters are vetted to use int properly */
  23 static inline int __firmware_loading_timeout(void)
  24 {
  25         return fw_fallback_config.loading_timeout;
  26 }
  27
  28 /* These setters are vetted to use int properly */
  29 static void __fw_fallback_set_timeout(int timeout)
  30 {
  31         fw_fallback_config.loading_timeout = timeout;
  32 }
  33
  34 /*
  35  * use small loading timeout for caching devices' firmware because all these
  36  * firmware images have been loaded successfully at lease once, also system is
  37  * ready for completing firmware loading now. The maximum size of firmware in
  38  * current distributions is about 2M bytes, so 10 secs should be enough.
  39  */
  40 void fw_fallback_set_cache_timeout(void)
  41 {
  42         fw_fallback_config.old_timeout = __firmware_loading_timeout();
  43         __fw_fallback_set_timeout(10);
  44 }
  45
  46 /* Restores the timeout to the value last configured during normal operation */
  47 void fw_fallback_set_default_timeout(void)
  48 {
  49         __fw_fallback_set_timeout(fw_fallback_config.old_timeout);
  50 }
  51
  52 static long firmware_loading_timeout(void)
  53 {
  54         return __firmware_loading_timeout() > 0 ?
  55                 __firmware_loading_timeout() * HZ : MAX_JIFFY_OFFSET;
  56 }
  57
  58 static inline bool fw_sysfs_done(struct fw_priv *fw_priv)
  59 {
  60         return __fw_state_check(fw_priv, FW_STATUS_DONE);
  61 }
  62
  63 static inline bool fw_sysfs_loading(struct fw_priv *fw_priv)
  64 {
  65         return __fw_state_check(fw_priv, FW_STATUS_LOADING);
  66 }
  67
  68 static inline int fw_sysfs_wait_timeout(struct fw_priv *fw_priv,  long timeout)
  69 {
  70         return __fw_state_wait_common(fw_priv, timeout);
  71 }
  72
  73 struct fw_sysfs {
  74         bool nowait;
  75         struct device dev;
  76         struct fw_priv *fw_priv;
  77         struct firmware *fw;
  78 };
  79
  80 static struct fw_sysfs *to_fw_sysfs(struct device *dev)
  81 {
  82         return container_of(dev, struct fw_sysfs, dev);
  83 }
  84
  85 static void __fw_load_abort(struct fw_priv *fw_priv)
  86 {
  87         /*
  88          * There is a small window in which user can write to 'loading'
  89          * between loading done and disappearance of 'loading'
  90          */
  91         if (fw_sysfs_done(fw_priv))
  92                 return;
  93
  94         list_del_init(&fw_priv->pending_list);
  95         fw_state_aborted(fw_priv);
  96 }
  97
  98 static void fw_load_abort(struct fw_sysfs *fw_sysfs)
  99 {
 100         struct fw_priv *fw_priv = fw_sysfs->fw_priv;
 101
 102         __fw_load_abort(fw_priv);
 103 }
 104
 105 static LIST_HEAD(pending_fw_head);
 106
 107 void kill_pending_fw_fallback_reqs(bool only_kill_custom)
 108 {
 109         struct fw_priv *fw_priv;
 110         struct fw_priv *next;
 111
 112         mutex_lock(&fw_lock);
 113         list_for_each_entry_safe(fw_priv, next, &pending_fw_head,
 114                                  pending_list) {
 115                 if (!fw_priv->need_uevent || !only_kill_custom)
 116                          __fw_load_abort(fw_priv);
 117         }
 118         mutex_unlock(&fw_lock);
 119 }
 120
 121 static ssize_t timeout_show(struct class *class, struct class_attribute *attr,
 122                             char *buf)
 123 {
 124         return sprintf(buf, "%d\n", __firmware_loading_timeout());
 125 }
 126
 127 /**
 128  * firmware_timeout_store() - set number of seconds to wait for firmware
 129  * @class: device class pointer
 130  * @attr: device attribute pointer
 131  * @buf: buffer to scan for timeout value
 132  * @count: number of bytes in @buf
 133  *
 134  *      Sets the number of seconds to wait for the firmware.  Once
 135  *      this expires an error will be returned to the driver and no
 136  *      firmware will be provided.
 137  *
 138  *      Note: zero means 'wait forever'.
 139  **/
 140 static ssize_t timeout_store(struct class *class, struct class_attribute *attr,
 141                              const char *buf, size_t count)
 142 {
 143         int tmp_loading_timeout = simple_strtol(buf, NULL, 10);
 144
 145         if (tmp_loading_timeout < 0)
 146                 tmp_loading_timeout = 0;
 147
 148         __fw_fallback_set_timeout(tmp_loading_timeout);
 149
 150         return count;
 151 }
 152 static CLASS_ATTR_RW(timeout);
 153
 154 static struct attribute *firmware_class_attrs[] = {
 155         &class_attr_timeout.attr,
 156         NULL,
 157 };
 158 ATTRIBUTE_GROUPS(firmware_class);
 159
 160 static void fw_dev_release(struct device *dev)
 161 {
 162         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 163
 164         kfree(fw_sysfs);
 165 }
 166
 167 static int do_firmware_uevent(struct fw_sysfs *fw_sysfs, struct kobj_uevent_env *env)
 168 {
 169         if (add_uevent_var(env, "FIRMWARE=%s", fw_sysfs->fw_priv->fw_name))
 170                 return -ENOMEM;
 171         if (add_uevent_var(env, "TIMEOUT=%i", __firmware_loading_timeout()))
 172                 return -ENOMEM;
 173         if (add_uevent_var(env, "ASYNC=%d", fw_sysfs->nowait))
 174                 return -ENOMEM;
 175
 176         return 0;
 177 }
 178
 179 static int firmware_uevent(struct device *dev, struct kobj_uevent_env *env)
 180 {
 181         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 182         int err = 0;
 183
 184         mutex_lock(&fw_lock);
 185         if (fw_sysfs->fw_priv)
 186                 err = do_firmware_uevent(fw_sysfs, env);
 187         mutex_unlock(&fw_lock);
 188         return err;
 189 }
 190
 191 static struct class firmware_class = {
 192         .name           = "firmware",
 193         .class_groups   = firmware_class_groups,
 194         .dev_uevent     = firmware_uevent,
 195         .dev_release    = fw_dev_release,
 196 };
 197
 198 int register_sysfs_loader(void)
 199 {
 200         return class_register(&firmware_class);
 201 }
 202
 203 void unregister_sysfs_loader(void)
 204 {
 205         class_unregister(&firmware_class);
 206 }
 207
 208 static ssize_t firmware_loading_show(struct device *dev,
 209                                      struct device_attribute *attr, char *buf)
 210 {
 211         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 212         int loading = 0;
 213
 214         mutex_lock(&fw_lock);
 215         if (fw_sysfs->fw_priv)
 216                 loading = fw_sysfs_loading(fw_sysfs->fw_priv);
 217         mutex_unlock(&fw_lock);
 218
 219         return sprintf(buf, "%d\n", loading);
 220 }
 221
 222 /* one pages buffer should be mapped/unmapped only once */
 223 static int map_fw_priv_pages(struct fw_priv *fw_priv)
 224 {
 225         if (!fw_priv->is_paged_buf)
 226                 return 0;
 227
 228         vunmap(fw_priv->data);
 229         fw_priv->data = vmap(fw_priv->pages, fw_priv->nr_pages, 0,
 230                              PAGE_KERNEL_RO);
 231         if (!fw_priv->data)
 232                 return -ENOMEM;
 233         return 0;
 234 }
 235
 236 /**
 237  * firmware_loading_store() - set value in the 'loading' control file
 238  * @dev: device pointer
 239  * @attr: device attribute pointer
 240  * @buf: buffer to scan for loading control value
 241  * @count: number of bytes in @buf
 242  *
 243  *      The relevant values are:
 244  *
 245  *       1: Start a load, discarding any previous partial load.
 246  *       0: Conclude the load and hand the data to the driver code.
 247  *      -1: Conclude the load with an error and discard any written data.
 248  **/
 249 static ssize_t firmware_loading_store(struct device *dev,
 250                                       struct device_attribute *attr,
 251                                       const char *buf, size_t count)
 252 {
 253         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 254         struct fw_priv *fw_priv;
 255         ssize_t written = count;
 256         int loading = simple_strtol(buf, NULL, 10);
 257         int i;
 258
 259         mutex_lock(&fw_lock);
 260         fw_priv = fw_sysfs->fw_priv;
 261         if (fw_state_is_aborted(fw_priv))
 262                 goto out;
 263
 264         switch (loading) {
 265         case 1:
 266                 /* discarding any previous partial load */
 267                 if (!fw_sysfs_done(fw_priv)) {
 268                         for (i = 0; i < fw_priv->nr_pages; i++)
 269                                 __free_page(fw_priv->pages[i]);
 270                         vfree(fw_priv->pages);
 271                         fw_priv->pages = NULL;
 272                         fw_priv->page_array_size = 0;
 273                         fw_priv->nr_pages = 0;
 274                         fw_state_start(fw_priv);
 275                 }
 276                 break;
 277         case 0:
 278                 if (fw_sysfs_loading(fw_priv)) {
 279                         int rc;
 280
 281                         /*
 282                          * Several loading requests may be pending on
 283                          * one same firmware buf, so let all requests
 284                          * see the mapped 'buf->data' once the loading
 285                          * is completed.
 286                          * */
 287                         rc = map_fw_priv_pages(fw_priv);
 288                         if (rc)
 289                                 dev_err(dev, "%s: map pages failed\n",
 290                                         __func__);
 291                         else
 292                                 rc = security_kernel_post_read_file(NULL,
 293                                                 fw_priv->data, fw_priv->size,
 294                                                 READING_FIRMWARE);
 295
 296                         /*
 297                          * Same logic as fw_load_abort, only the DONE bit
 298                          * is ignored and we set ABORT only on failure.
 299                          */
 300                         list_del_init(&fw_priv->pending_list);
 301                         if (rc) {
 302                                 fw_state_aborted(fw_priv);
 303                                 written = rc;
 304                         } else {
 305                                 fw_state_done(fw_priv);
 306                         }
 307                         break;
 308                 }
 309                 /* fallthrough */
 310         default:
 311                 dev_err(dev, "%s: unexpected value (%d)\n", __func__, loading);
 312                 /* fallthrough */
 313         case -1:
 314                 fw_load_abort(fw_sysfs);
 315                 break;
 316         }
 317 out:
 318         mutex_unlock(&fw_lock);
 319         return written;
 320 }
 321
 322 static DEVICE_ATTR(loading, 0644, firmware_loading_show, firmware_loading_store);
 323
 324 static void firmware_rw_data(struct fw_priv *fw_priv, char *buffer,
 325                            loff_t offset, size_t count, bool read)
 326 {
 327         if (read)
 328                 memcpy(buffer, fw_priv->data + offset, count);
 329         else
 330                 memcpy(fw_priv->data + offset, buffer, count);
 331 }
 332
 333 static void firmware_rw(struct fw_priv *fw_priv, char *buffer,
 334                         loff_t offset, size_t count, bool read)
 335 {
 336         while (count) {
 337                 void *page_data;
 338                 int page_nr = offset >> PAGE_SHIFT;
 339                 int page_ofs = offset & (PAGE_SIZE-1);
 340                 int page_cnt = min_t(size_t, PAGE_SIZE - page_ofs, count);
 341
 342                 page_data = kmap(fw_priv->pages[page_nr]);
 343
 344                 if (read)
 345                         memcpy(buffer, page_data + page_ofs, page_cnt);
 346                 else
 347                         memcpy(page_data + page_ofs, buffer, page_cnt);
 348
 349                 kunmap(fw_priv->pages[page_nr]);
 350                 buffer += page_cnt;
 351                 offset += page_cnt;
 352                 count -= page_cnt;
 353         }
 354 }
 355
 356 static ssize_t firmware_data_read(struct file *filp, struct kobject *kobj,
 357                                   struct bin_attribute *bin_attr,
 358                                   char *buffer, loff_t offset, size_t count)
 359 {
 360         struct device *dev = kobj_to_dev(kobj);
 361         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 362         struct fw_priv *fw_priv;
 363         ssize_t ret_count;
 364
 365         mutex_lock(&fw_lock);
 366         fw_priv = fw_sysfs->fw_priv;
 367         if (!fw_priv || fw_sysfs_done(fw_priv)) {
 368                 ret_count = -ENODEV;
 369                 goto out;
 370         }
 371         if (offset > fw_priv->size) {
 372                 ret_count = 0;
 373                 goto out;
 374         }
 375         if (count > fw_priv->size - offset)
 376                 count = fw_priv->size - offset;
 377
 378         ret_count = count;
 379
 380         if (fw_priv->data)
 381                 firmware_rw_data(fw_priv, buffer, offset, count, true);
 382         else
 383                 firmware_rw(fw_priv, buffer, offset, count, true);
 384
 385 out:
 386         mutex_unlock(&fw_lock);
 387         return ret_count;
 388 }
 389
 390 static int fw_realloc_pages(struct fw_sysfs *fw_sysfs, int min_size)
 391 {
 392         struct fw_priv *fw_priv= fw_sysfs->fw_priv;
 393         int pages_needed = PAGE_ALIGN(min_size) >> PAGE_SHIFT;
 394
 395         /* If the array of pages is too small, grow it... */
 396         if (fw_priv->page_array_size < pages_needed) {
 397                 int new_array_size = max(pages_needed,
 398                                          fw_priv->page_array_size * 2);
 399                 struct page **new_pages;
 400
 401                 new_pages = vmalloc(array_size(new_array_size, sizeof(void *)));
 402                 if (!new_pages) {
 403                         fw_load_abort(fw_sysfs);
 404                         return -ENOMEM;
 405                 }
 406                 memcpy(new_pages, fw_priv->pages,
 407                        fw_priv->page_array_size * sizeof(void *));
 408                 memset(&new_pages[fw_priv->page_array_size], 0, sizeof(void *) *
 409                        (new_array_size - fw_priv->page_array_size));
 410                 vfree(fw_priv->pages);
 411                 fw_priv->pages = new_pages;
 412                 fw_priv->page_array_size = new_array_size;
 413         }
 414
 415         while (fw_priv->nr_pages < pages_needed) {
 416                 fw_priv->pages[fw_priv->nr_pages] =
 417                         alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
 418
 419                 if (!fw_priv->pages[fw_priv->nr_pages]) {
 420                         fw_load_abort(fw_sysfs);
 421                         return -ENOMEM;
 422                 }
 423                 fw_priv->nr_pages++;
 424         }
 425         return 0;
 426 }
 427
 428 /**
 429  * firmware_data_write() - write method for firmware
 430  * @filp: open sysfs file
 431  * @kobj: kobject for the device
 432  * @bin_attr: bin_attr structure
 433  * @buffer: buffer being written
 434  * @offset: buffer offset for write in total data store area
 435  * @count: buffer size
 436  *
 437  *      Data written to the 'data' attribute will be later handed to
 438  *      the driver as a firmware image.
 439  **/
 440 static ssize_t firmware_data_write(struct file *filp, struct kobject *kobj,
 441                                    struct bin_attribute *bin_attr,
 442                                    char *buffer, loff_t offset, size_t count)
 443 {
 444         struct device *dev = kobj_to_dev(kobj);
 445         struct fw_sysfs *fw_sysfs = to_fw_sysfs(dev);
 446         struct fw_priv *fw_priv;
 447         ssize_t retval;
 448
 449         if (!capable(CAP_SYS_RAWIO))
 450                 return -EPERM;
 451
 452         mutex_lock(&fw_lock);
 453         fw_priv = fw_sysfs->fw_priv;
 454         if (!fw_priv || fw_sysfs_done(fw_priv)) {
 455                 retval = -ENODEV;
 456                 goto out;
 457         }
 458
 459         if (fw_priv->data) {
 460                 if (offset + count > fw_priv->allocated_size) {
 461                         retval = -ENOMEM;
 462                         goto out;
 463                 }
 464                 firmware_rw_data(fw_priv, buffer, offset, count, false);
 465                 retval = count;
 466         } else {
 467                 retval = fw_realloc_pages(fw_sysfs, offset + count);
 468                 if (retval)
 469                         goto out;
 470
 471                 retval = count;
 472                 firmware_rw(fw_priv, buffer, offset, count, false);
 473         }
 474
 475         fw_priv->size = max_t(size_t, offset + count, fw_priv->size);
 476 out:
 477         mutex_unlock(&fw_lock);
 478         return retval;
 479 }
 480
 481 static struct bin_attribute firmware_attr_data = {
 482         .attr = { .name = "data", .mode = 0644 },
 483         .size = 0,
 484         .read = firmware_data_read,
 485         .write = firmware_data_write,
 486 };
 487
 488 static struct attribute *fw_dev_attrs[] = {
 489         &dev_attr_loading.attr,
 490         NULL
 491 };
 492
 493 static struct bin_attribute *fw_dev_bin_attrs[] = {
 494         &firmware_attr_data,
 495         NULL
 496 };
 497
 498 static const struct attribute_group fw_dev_attr_group = {
 499         .attrs = fw_dev_attrs,
 500         .bin_attrs = fw_dev_bin_attrs,
 501 };
 502
 503 static const struct attribute_group *fw_dev_attr_groups[] = {
 504         &fw_dev_attr_group,
 505         NULL
 506 };
 507
 508 static struct fw_sysfs *
 509 fw_create_instance(struct firmware *firmware, const char *fw_name,
 510                    struct device *device, enum fw_opt opt_flags)
 511 {
 512         struct fw_sysfs *fw_sysfs;
 513         struct device *f_dev;
 514
 515         fw_sysfs = kzalloc(sizeof(*fw_sysfs), GFP_KERNEL);
 516         if (!fw_sysfs) {
 517                 fw_sysfs = ERR_PTR(-ENOMEM);
 518                 goto exit;
 519         }
 520
 521         fw_sysfs->nowait = !!(opt_flags & FW_OPT_NOWAIT);
 522         fw_sysfs->fw = firmware;
 523         f_dev = &fw_sysfs->dev;
 524
 525         device_initialize(f_dev);
 526         dev_set_name(f_dev, "%s", fw_name);
 527         f_dev->parent = device;
 528         f_dev->class = &firmware_class;
 529         f_dev->groups = fw_dev_attr_groups;
 530 exit:
 531         return fw_sysfs;
 532 }
 533
 534 /**
 535  * fw_load_sysfs_fallback() - load a firmware via the sysfs fallback mechanism
 536  * @fw_sysfs: firmware sysfs information for the firmware to load
 537  * @opt_flags: flags of options, FW_OPT_*
 538  * @timeout: timeout to wait for the load
 539  *
 540  * In charge of constructing a sysfs fallback interface for firmware loading.
 541  **/
 542 static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs,
 543                                   enum fw_opt opt_flags, long timeout)
 544 {
 545         int retval = 0;
 546         struct device *f_dev = &fw_sysfs->dev;
 547         struct fw_priv *fw_priv = fw_sysfs->fw_priv;
 548
 549         /* fall back on userspace loading */
 550         if (!fw_priv->data)
 551                 fw_priv->is_paged_buf = true;
 552
 553         dev_set_uevent_suppress(f_dev, true);
 554
 555         retval = device_add(f_dev);
 556         if (retval) {
 557                 dev_err(f_dev, "%s: device_register failed\n", __func__);
 558                 goto err_put_dev;
 559         }
 560
 561         mutex_lock(&fw_lock);
 562         list_add(&fw_priv->pending_list, &pending_fw_head);
 563         mutex_unlock(&fw_lock);
 564
 565         if (opt_flags & FW_OPT_UEVENT) {
 566                 fw_priv->need_uevent = true;
 567                 dev_set_uevent_suppress(f_dev, false);
 568                 dev_dbg(f_dev, "firmware: requesting %s\n", fw_priv->fw_name);
 569                 kobject_uevent(&fw_sysfs->dev.kobj, KOBJ_ADD);
 570         } else {
 571                 timeout = MAX_JIFFY_OFFSET;
 572         }
 573
 574         retval = fw_sysfs_wait_timeout(fw_priv, timeout);
 575         if (retval < 0) {
 576                 mutex_lock(&fw_lock);
 577                 fw_load_abort(fw_sysfs);
 578                 mutex_unlock(&fw_lock);
 579         }
 580
 581         if (fw_state_is_aborted(fw_priv)) {
 582                 if (retval == -ERESTARTSYS)
 583                         retval = -EINTR;
 584                 else
 585                         retval = -EAGAIN;
 586         } else if (fw_priv->is_paged_buf && !fw_priv->data)
 587                 retval = -ENOMEM;
 588
 589         device_del(f_dev);
 590 err_put_dev:
 591         put_device(f_dev);
 592         return retval;
 593 }
 594
 595 static int fw_load_from_user_helper(struct firmware *firmware,
 596                                     const char *name, struct device *device,
 597                                     enum fw_opt opt_flags)
 598 {
 599         struct fw_sysfs *fw_sysfs;
 600         long timeout;
 601         int ret;
 602
 603         timeout = firmware_loading_timeout();
 604         if (opt_flags & FW_OPT_NOWAIT) {
 605                 timeout = usermodehelper_read_lock_wait(timeout);
 606                 if (!timeout) {
 607                         dev_dbg(device, "firmware: %s loading timed out\n",
 608                                 name);
 609                         return -EBUSY;
 610                 }
 611         } else {
 612                 ret = usermodehelper_read_trylock();
 613                 if (WARN_ON(ret)) {
 614                         dev_err(device, "firmware: %s will not be loaded\n",
 615                                 name);
 616                         return ret;
 617                 }
 618         }
 619
 620         fw_sysfs = fw_create_instance(firmware, name, device, opt_flags);
 621         if (IS_ERR(fw_sysfs)) {
 622                 ret = PTR_ERR(fw_sysfs);
 623                 goto out_unlock;
 624         }
 625
 626         fw_sysfs->fw_priv = firmware->priv;
 627         ret = fw_load_sysfs_fallback(fw_sysfs, opt_flags, timeout);
 628
 629         if (!ret)
 630                 ret = assign_fw(firmware, device, opt_flags);
 631
 632 out_unlock:
 633         usermodehelper_read_unlock();
 634
 635         return ret;
 636 }
 637
 638 static bool fw_force_sysfs_fallback(enum fw_opt opt_flags)
 639 {
 640         if (fw_fallback_config.force_sysfs_fallback)
 641                 return true;
 642         if (!(opt_flags & FW_OPT_USERHELPER))
 643                 return false;
 644         return true;
 645 }
 646
 647 static bool fw_run_sysfs_fallback(enum fw_opt opt_flags)
 648 {
 649         int ret;
 650
 651         if (fw_fallback_config.ignore_sysfs_fallback) {
 652                 pr_info_once("Ignoring firmware sysfs fallback due to sysctl knob\n");
 653                 return false;
 654         }
 655
 656         if ((opt_flags & FW_OPT_NOFALLBACK))
 657                 return false;
 658
 659         /* Also permit LSMs and IMA to fail firmware sysfs fallback */
 660         ret = security_kernel_load_data(LOADING_FIRMWARE);
 661         if (ret < 0)
 662                 return ret;
 663
 664         return fw_force_sysfs_fallback(opt_flags);
 665 }
 666
 667 /**
 668  * firmware_fallback_sysfs() - use the fallback mechanism to find firmware
 669  * @fw: pointer to firmware image
 670  * @name: name of firmware file to look for
 671  * @device: device for which firmware is being loaded
 672  * @opt_flags: options to control firmware loading behaviour
 673  * @ret: return value from direct lookup which triggered the fallback mechanism
 674  *
 675  * This function is called if direct lookup for the firmware failed, it enables
 676  * a fallback mechanism through userspace by exposing a sysfs loading
 677  * interface. Userspace is in charge of loading the firmware through the syfs
 678  * loading interface. This syfs fallback mechanism may be disabled completely
 679  * on a system by setting the proc sysctl value ignore_sysfs_fallback to true.
 680  * If this false we check if the internal API caller set the @FW_OPT_NOFALLBACK
 681  * flag, if so it would also disable the fallback mechanism. A system may want
 682  * to enfoce the sysfs fallback mechanism at all times, it can do this by
 683  * setting ignore_sysfs_fallback to false and force_sysfs_fallback to true.
 684  * Enabling force_sysfs_fallback is functionally equivalent to build a kernel
 685  * with CONFIG_FW_LOADER_USER_HELPER_FALLBACK.
 686  **/
 687 int firmware_fallback_sysfs(struct firmware *fw, const char *name,
 688                             struct device *device,
 689                             enum fw_opt opt_flags,
 690                             int ret)
 691 {
 692         if (!fw_run_sysfs_fallback(opt_flags))
 693                 return ret;
 694
 695         if (!(opt_flags & FW_OPT_NO_WARN))
 696                 dev_warn(device, "Falling back to syfs fallback for: %s\n",
 697                                  name);
 698         else
 699                 dev_dbg(device, "Falling back to sysfs fallback for: %s\n",
 700                                 name);
 701         return fw_load_from_user_helper(fw, name, device, opt_flags);
 702 }