drivers/hwtracing/stm/core.c

   1 /*
   2  * System Trace Module (STM) infrastructure
   3  * Copyright (c) 2014, Intel Corporation.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms and conditions of the GNU General Public License,
   7  * version 2, as published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  12  * more details.
  13  *
  14  * STM class implements generic infrastructure for  System Trace Module devices
  15  * as defined in MIPI STPv2 specification.
  16  */
  17
  18 #include <linux/uaccess.h>
  19 #include <linux/kernel.h>
  20 #include <linux/module.h>
  21 #include <linux/device.h>
  22 #include <linux/compat.h>
  23 #include <linux/kdev_t.h>
  24 #include <linux/srcu.h>
  25 #include <linux/slab.h>
  26 #include <linux/stm.h>
  27 #include <linux/fs.h>
  28 #include <linux/mm.h>
  29 #include "stm.h"
  30
  31 #include <uapi/linux/stm.h>
  32
  33 static unsigned int stm_core_up;
  34
  35 /*
  36  * The SRCU here makes sure that STM device doesn't disappear from under a
  37  * stm_source_write() caller, which may want to have as little overhead as
  38  * possible.
  39  */
  40 static struct srcu_struct stm_source_srcu;
  41
  42 static ssize_t masters_show(struct device *dev,
  43                             struct device_attribute *attr,
  44                             char *buf)
  45 {
  46         struct stm_device *stm = to_stm_device(dev);
  47         int ret;
  48
  49         ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
  50
  51         return ret;
  52 }
  53
  54 static DEVICE_ATTR_RO(masters);
  55
  56 static ssize_t channels_show(struct device *dev,
  57                              struct device_attribute *attr,
  58                              char *buf)
  59 {
  60         struct stm_device *stm = to_stm_device(dev);
  61         int ret;
  62
  63         ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
  64
  65         return ret;
  66 }
  67
  68 static DEVICE_ATTR_RO(channels);
  69
  70 static struct attribute *stm_attrs[] = {
  71         &dev_attr_masters.attr,
  72         &dev_attr_channels.attr,
  73         NULL,
  74 };
  75
  76 ATTRIBUTE_GROUPS(stm);
  77
  78 static struct class stm_class = {
  79         .name           = "stm",
  80         .dev_groups     = stm_groups,
  81 };
  82
  83 static int stm_dev_match(struct device *dev, const void *data)
  84 {
  85         const char *name = data;
  86
  87         return sysfs_streq(name, dev_name(dev));
  88 }
  89
  90 /**
  91  * stm_find_device() - find stm device by name
  92  * @buf:        character buffer containing the name
  93  *
  94  * This is called when either policy gets assigned to an stm device or an
  95  * stm_source device gets linked to an stm device.
  96  *
  97  * This grabs device's reference (get_device()) and module reference, both
  98  * of which the calling path needs to make sure to drop with stm_put_device().
  99  *
 100  * Return:      stm device pointer or null if lookup failed.
 101  */
 102 struct stm_device *stm_find_device(const char *buf)
 103 {
 104         struct stm_device *stm;
 105         struct device *dev;
 106
 107         if (!stm_core_up)
 108                 return NULL;
 109
 110         dev = class_find_device(&stm_class, NULL, buf, stm_dev_match);
 111         if (!dev)
 112                 return NULL;
 113
 114         stm = to_stm_device(dev);
 115         if (!try_module_get(stm->owner)) {
 116                 /* matches class_find_device() above */
 117                 put_device(dev);
 118                 return NULL;
 119         }
 120
 121         return stm;
 122 }
 123
 124 /**
 125  * stm_put_device() - drop references on the stm device
 126  * @stm:        stm device, previously acquired by stm_find_device()
 127  *
 128  * This drops the module reference and device reference taken by
 129  * stm_find_device() or stm_char_open().
 130  */
 131 void stm_put_device(struct stm_device *stm)
 132 {
 133         module_put(stm->owner);
 134         put_device(&stm->dev);
 135 }
 136
 137 /*
 138  * Internally we only care about software-writable masters here, that is the
 139  * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
 140  * original master numbers to be visible externally, since they are the ones
 141  * that will appear in the STP stream. Thus, the internal bookkeeping uses
 142  * $master - stm_data->sw_start to reference master descriptors and such.
 143  */
 144
 145 #define __stm_master(_s, _m)                            \
 146         ((_s)->masters[(_m) - (_s)->data->sw_start])
 147
 148 static inline struct stp_master *
 149 stm_master(struct stm_device *stm, unsigned int idx)
 150 {
 151         if (idx < stm->data->sw_start || idx > stm->data->sw_end)
 152                 return NULL;
 153
 154         return __stm_master(stm, idx);
 155 }
 156
 157 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
 158 {
 159         struct stp_master *master;
 160         size_t size;
 161
 162         size = ALIGN(stm->data->sw_nchannels, 8) / 8;
 163         size += sizeof(struct stp_master);
 164         master = kzalloc(size, GFP_ATOMIC);
 165         if (!master)
 166                 return -ENOMEM;
 167
 168         master->nr_free = stm->data->sw_nchannels;
 169         __stm_master(stm, idx) = master;
 170
 171         return 0;
 172 }
 173
 174 static void stp_master_free(struct stm_device *stm, unsigned int idx)
 175 {
 176         struct stp_master *master = stm_master(stm, idx);
 177
 178         if (!master)
 179                 return;
 180
 181         __stm_master(stm, idx) = NULL;
 182         kfree(master);
 183 }
 184
 185 static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
 186 {
 187         struct stp_master *master = stm_master(stm, output->master);
 188
 189         lockdep_assert_held(&stm->mc_lock);
 190         lockdep_assert_held(&output->lock);
 191
 192         if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
 193                 return;
 194
 195         bitmap_allocate_region(&master->chan_map[0], output->channel,
 196                                ilog2(output->nr_chans));
 197
 198         master->nr_free -= output->nr_chans;
 199 }
 200
 201 static void
 202 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
 203 {
 204         struct stp_master *master = stm_master(stm, output->master);
 205
 206         lockdep_assert_held(&stm->mc_lock);
 207         lockdep_assert_held(&output->lock);
 208
 209         bitmap_release_region(&master->chan_map[0], output->channel,
 210                               ilog2(output->nr_chans));
 211
 212         output->nr_chans = 0;
 213         master->nr_free += output->nr_chans;
 214 }
 215
 216 /*
 217  * This is like bitmap_find_free_region(), except it can ignore @start bits
 218  * at the beginning.
 219  */
 220 static int find_free_channels(unsigned long *bitmap, unsigned int start,
 221                               unsigned int end, unsigned int width)
 222 {
 223         unsigned int pos;
 224         int i;
 225
 226         for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
 227                 pos = find_next_zero_bit(bitmap, end + 1, pos);
 228                 if (pos + width > end + 1)
 229                         break;
 230
 231                 if (pos & (width - 1))
 232                         continue;
 233
 234                 for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
 235                         ;
 236                 if (i == width)
 237                         return pos;
 238         }
 239
 240         return -1;
 241 }
 242
 243 static int
 244 stm_find_master_chan(struct stm_device *stm, unsigned int width,
 245                      unsigned int *mstart, unsigned int mend,
 246                      unsigned int *cstart, unsigned int cend)
 247 {
 248         struct stp_master *master;
 249         unsigned int midx;
 250         int pos, err;
 251
 252         for (midx = *mstart; midx <= mend; midx++) {
 253                 if (!stm_master(stm, midx)) {
 254                         err = stp_master_alloc(stm, midx);
 255                         if (err)
 256                                 return err;
 257                 }
 258
 259                 master = stm_master(stm, midx);
 260
 261                 if (!master->nr_free)
 262                         continue;
 263
 264                 pos = find_free_channels(master->chan_map, *cstart, cend,
 265                                          width);
 266                 if (pos < 0)
 267                         continue;
 268
 269                 *mstart = midx;
 270                 *cstart = pos;
 271                 return 0;
 272         }
 273
 274         return -ENOSPC;
 275 }
 276
 277 static int stm_output_assign(struct stm_device *stm, unsigned int width,
 278                              struct stp_policy_node *policy_node,
 279                              struct stm_output *output)
 280 {
 281         unsigned int midx, cidx, mend, cend;
 282         int ret = -EINVAL;
 283
 284         if (width > stm->data->sw_nchannels)
 285                 return -EINVAL;
 286
 287         if (policy_node) {
 288                 stp_policy_node_get_ranges(policy_node,
 289                                            &midx, &mend, &cidx, &cend);
 290         } else {
 291                 midx = stm->data->sw_start;
 292                 cidx = 0;
 293                 mend = stm->data->sw_end;
 294                 cend = stm->data->sw_nchannels - 1;
 295         }
 296
 297         spin_lock(&stm->mc_lock);
 298         spin_lock(&output->lock);
 299         /* output is already assigned -- shouldn't happen */
 300         if (WARN_ON_ONCE(output->nr_chans))
 301                 goto unlock;
 302
 303         ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
 304         if (ret < 0)
 305                 goto unlock;
 306
 307         output->master = midx;
 308         output->channel = cidx;
 309         output->nr_chans = width;
 310         stm_output_claim(stm, output);
 311         dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
 312
 313         ret = 0;
 314 unlock:
 315         spin_unlock(&output->lock);
 316         spin_unlock(&stm->mc_lock);
 317
 318         return ret;
 319 }
 320
 321 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
 322 {
 323         spin_lock(&stm->mc_lock);
 324         spin_lock(&output->lock);
 325         if (output->nr_chans)
 326                 stm_output_disclaim(stm, output);
 327         spin_unlock(&output->lock);
 328         spin_unlock(&stm->mc_lock);
 329 }
 330
 331 static void stm_output_init(struct stm_output *output)
 332 {
 333         spin_lock_init(&output->lock);
 334 }
 335
 336 static int major_match(struct device *dev, const void *data)
 337 {
 338         unsigned int major = *(unsigned int *)data;
 339
 340         return MAJOR(dev->devt) == major;
 341 }
 342
 343 static int stm_char_open(struct inode *inode, struct file *file)
 344 {
 345         struct stm_file *stmf;
 346         struct device *dev;
 347         unsigned int major = imajor(inode);
 348         int err = -ENODEV;
 349
 350         dev = class_find_device(&stm_class, NULL, &major, major_match);
 351         if (!dev)
 352                 return -ENODEV;
 353
 354         stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
 355         if (!stmf)
 356                 return -ENOMEM;
 357
 358         stm_output_init(&stmf->output);
 359         stmf->stm = to_stm_device(dev);
 360
 361         if (!try_module_get(stmf->stm->owner))
 362                 goto err_free;
 363
 364         file->private_data = stmf;
 365
 366         return nonseekable_open(inode, file);
 367
 368 err_free:
 369         /* matches class_find_device() above */
 370         put_device(dev);
 371         kfree(stmf);
 372
 373         return err;
 374 }
 375
 376 static int stm_char_release(struct inode *inode, struct file *file)
 377 {
 378         struct stm_file *stmf = file->private_data;
 379         struct stm_device *stm = stmf->stm;
 380
 381         if (stm->data->unlink)
 382                 stm->data->unlink(stm->data, stmf->output.master,
 383                                   stmf->output.channel);
 384
 385         stm_output_free(stm, &stmf->output);
 386
 387         /*
 388          * matches the stm_char_open()'s
 389          * class_find_device() + try_module_get()
 390          */
 391         stm_put_device(stm);
 392         kfree(stmf);
 393
 394         return 0;
 395 }
 396
 397 static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
 398 {
 399         struct stm_device *stm = stmf->stm;
 400         int ret;
 401
 402         stmf->policy_node = stp_policy_node_lookup(stm, id);
 403
 404         ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
 405
 406         if (stmf->policy_node)
 407                 stp_policy_node_put(stmf->policy_node);
 408
 409         return ret;
 410 }
 411
 412 static ssize_t stm_write(struct stm_data *data, unsigned int master,
 413                           unsigned int channel, const char *buf, size_t count)
 414 {
 415         unsigned int flags = STP_PACKET_TIMESTAMPED;
 416         const unsigned char *p = buf, nil = 0;
 417         size_t pos;
 418         ssize_t sz;
 419
 420         for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
 421                 sz = min_t(unsigned int, count - pos, 8);
 422                 sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
 423                                   sz, p);
 424                 flags = 0;
 425
 426                 if (sz < 0)
 427                         break;
 428         }
 429
 430         data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
 431
 432         return pos;
 433 }
 434
 435 static ssize_t stm_char_write(struct file *file, const char __user *buf,
 436                               size_t count, loff_t *ppos)
 437 {
 438         struct stm_file *stmf = file->private_data;
 439         struct stm_device *stm = stmf->stm;
 440         char *kbuf;
 441         int err;
 442
 443         if (count + 1 > PAGE_SIZE)
 444                 count = PAGE_SIZE - 1;
 445
 446         /*
 447          * if no m/c have been assigned to this writer up to this
 448          * point, use "default" policy entry
 449          */
 450         if (!stmf->output.nr_chans) {
 451                 err = stm_file_assign(stmf, "default", 1);
 452                 /*
 453                  * EBUSY means that somebody else just assigned this
 454                  * output, which is just fine for write()
 455                  */
 456                 if (err && err != -EBUSY)
 457                         return err;
 458         }
 459
 460         kbuf = kmalloc(count + 1, GFP_KERNEL);
 461         if (!kbuf)
 462                 return -ENOMEM;
 463
 464         err = copy_from_user(kbuf, buf, count);
 465         if (err) {
 466                 kfree(kbuf);
 467                 return -EFAULT;
 468         }
 469
 470         count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
 471                           kbuf, count);
 472
 473         kfree(kbuf);
 474
 475         return count;
 476 }
 477
 478 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 479 {
 480         struct stm_file *stmf = file->private_data;
 481         struct stm_device *stm = stmf->stm;
 482         unsigned long size, phys;
 483
 484         if (!stm->data->mmio_addr)
 485                 return -EOPNOTSUPP;
 486
 487         if (vma->vm_pgoff)
 488                 return -EINVAL;
 489
 490         size = vma->vm_end - vma->vm_start;
 491
 492         if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
 493                 return -EINVAL;
 494
 495         phys = stm->data->mmio_addr(stm->data, stmf->output.master,
 496                                     stmf->output.channel,
 497                                     stmf->output.nr_chans);
 498
 499         if (!phys)
 500                 return -EINVAL;
 501
 502         vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 503         vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 504         vm_iomap_memory(vma, phys, size);
 505
 506         return 0;
 507 }
 508
 509 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 510 {
 511         struct stm_device *stm = stmf->stm;
 512         struct stp_policy_id *id;
 513         int ret = -EINVAL;
 514         u32 size;
 515
 516         if (stmf->output.nr_chans)
 517                 return -EBUSY;
 518
 519         if (copy_from_user(&size, arg, sizeof(size)))
 520                 return -EFAULT;
 521
 522         if (size >= PATH_MAX + sizeof(*id))
 523                 return -EINVAL;
 524
 525         /*
 526          * size + 1 to make sure the .id string at the bottom is terminated,
 527          * which is also why memdup_user() is not useful here
 528          */
 529         id = kzalloc(size + 1, GFP_KERNEL);
 530         if (!id)
 531                 return -ENOMEM;
 532
 533         if (copy_from_user(id, arg, size)) {
 534                 ret = -EFAULT;
 535                 goto err_free;
 536         }
 537
 538         if (id->__reserved_0 || id->__reserved_1)
 539                 goto err_free;
 540
 541         if (id->width < 1 ||
 542             id->width > PAGE_SIZE / stm->data->sw_mmiosz)
 543                 goto err_free;
 544
 545         ret = stm_file_assign(stmf, id->id, id->width);
 546         if (ret)
 547                 goto err_free;
 548
 549         ret = 0;
 550
 551         if (stm->data->link)
 552                 ret = stm->data->link(stm->data, stmf->output.master,
 553                                       stmf->output.channel);
 554
 555         if (ret)
 556                 stm_output_free(stmf->stm, &stmf->output);
 557
 558 err_free:
 559         kfree(id);
 560
 561         return ret;
 562 }
 563
 564 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
 565 {
 566         struct stp_policy_id id = {
 567                 .size           = sizeof(id),
 568                 .master         = stmf->output.master,
 569                 .channel        = stmf->output.channel,
 570                 .width          = stmf->output.nr_chans,
 571                 .__reserved_0   = 0,
 572                 .__reserved_1   = 0,
 573         };
 574
 575         return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
 576 }
 577
 578 static long
 579 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 580 {
 581         struct stm_file *stmf = file->private_data;
 582         struct stm_data *stm_data = stmf->stm->data;
 583         int err = -ENOTTY;
 584         u64 options;
 585
 586         switch (cmd) {
 587         case STP_POLICY_ID_SET:
 588                 err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
 589                 if (err)
 590                         return err;
 591
 592                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 593
 594         case STP_POLICY_ID_GET:
 595                 return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
 596
 597         case STP_SET_OPTIONS:
 598                 if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
 599                         return -EFAULT;
 600
 601                 if (stm_data->set_options)
 602                         err = stm_data->set_options(stm_data,
 603                                                     stmf->output.master,
 604                                                     stmf->output.channel,
 605                                                     stmf->output.nr_chans,
 606                                                     options);
 607
 608                 break;
 609         default:
 610                 break;
 611         }
 612
 613         return err;
 614 }
 615
 616 #ifdef CONFIG_COMPAT
 617 static long
 618 stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 619 {
 620         return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
 621 }
 622 #else
 623 #define stm_char_compat_ioctl   NULL
 624 #endif
 625
 626 static const struct file_operations stm_fops = {
 627         .open           = stm_char_open,
 628         .release        = stm_char_release,
 629         .write          = stm_char_write,
 630         .mmap           = stm_char_mmap,
 631         .unlocked_ioctl = stm_char_ioctl,
 632         .compat_ioctl   = stm_char_compat_ioctl,
 633         .llseek         = no_llseek,
 634 };
 635
 636 static void stm_device_release(struct device *dev)
 637 {
 638         struct stm_device *stm = to_stm_device(dev);
 639
 640         kfree(stm);
 641 }
 642
 643 int stm_register_device(struct device *parent, struct stm_data *stm_data,
 644                         struct module *owner)
 645 {
 646         struct stm_device *stm;
 647         unsigned int nmasters;
 648         int err = -ENOMEM;
 649
 650         if (!stm_core_up)
 651                 return -EPROBE_DEFER;
 652
 653         if (!stm_data->packet || !stm_data->sw_nchannels)
 654                 return -EINVAL;
 655
 656         nmasters = stm_data->sw_end - stm_data->sw_start + 1;
 657         stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
 658         if (!stm)
 659                 return -ENOMEM;
 660
 661         stm->major = register_chrdev(0, stm_data->name, &stm_fops);
 662         if (stm->major < 0)
 663                 goto err_free;
 664
 665         device_initialize(&stm->dev);
 666         stm->dev.devt = MKDEV(stm->major, 0);
 667         stm->dev.class = &stm_class;
 668         stm->dev.parent = parent;
 669         stm->dev.release = stm_device_release;
 670
 671         err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
 672         if (err)
 673                 goto err_device;
 674
 675         err = device_add(&stm->dev);
 676         if (err)
 677                 goto err_device;
 678
 679         mutex_init(&stm->link_mutex);
 680         spin_lock_init(&stm->link_lock);
 681         INIT_LIST_HEAD(&stm->link_list);
 682
 683         spin_lock_init(&stm->mc_lock);
 684         mutex_init(&stm->policy_mutex);
 685         stm->sw_nmasters = nmasters;
 686         stm->owner = owner;
 687         stm->data = stm_data;
 688         stm_data->stm = stm;
 689
 690         return 0;
 691
 692 err_device:
 693         /* matches device_initialize() above */
 694         put_device(&stm->dev);
 695 err_free:
 696         kfree(stm);
 697
 698         return err;
 699 }
 700 EXPORT_SYMBOL_GPL(stm_register_device);
 701
 702 static int __stm_source_link_drop(struct stm_source_device *src,
 703                                   struct stm_device *stm);
 704
 705 void stm_unregister_device(struct stm_data *stm_data)
 706 {
 707         struct stm_device *stm = stm_data->stm;
 708         struct stm_source_device *src, *iter;
 709         int i, ret;
 710
 711         mutex_lock(&stm->link_mutex);
 712         list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
 713                 ret = __stm_source_link_drop(src, stm);
 714                 /*
 715                  * src <-> stm link must not change under the same
 716                  * stm::link_mutex, so complain loudly if it has;
 717                  * also in this situation ret!=0 means this src is
 718                  * not connected to this stm and it should be otherwise
 719                  * safe to proceed with the tear-down of stm.
 720                  */
 721                 WARN_ON_ONCE(ret);
 722         }
 723         mutex_unlock(&stm->link_mutex);
 724
 725         synchronize_srcu(&stm_source_srcu);
 726
 727         unregister_chrdev(stm->major, stm_data->name);
 728
 729         mutex_lock(&stm->policy_mutex);
 730         if (stm->policy)
 731                 stp_policy_unbind(stm->policy);
 732         mutex_unlock(&stm->policy_mutex);
 733
 734         for (i = stm->data->sw_start; i <= stm->data->sw_end; i++)
 735                 stp_master_free(stm, i);
 736
 737         device_unregister(&stm->dev);
 738         stm_data->stm = NULL;
 739 }
 740 EXPORT_SYMBOL_GPL(stm_unregister_device);
 741
 742 /*
 743  * stm::link_list access serialization uses a spinlock and a mutex; holding
 744  * either of them guarantees that the list is stable; modification requires
 745  * holding both of them.
 746  *
 747  * Lock ordering is as follows:
 748  *   stm::link_mutex
 749  *     stm::link_lock
 750  *       src::link_lock
 751  */
 752
 753 /**
 754  * stm_source_link_add() - connect an stm_source device to an stm device
 755  * @src:        stm_source device
 756  * @stm:        stm device
 757  *
 758  * This function establishes a link from stm_source to an stm device so that
 759  * the former can send out trace data to the latter.
 760  *
 761  * Return:      0 on success, -errno otherwise.
 762  */
 763 static int stm_source_link_add(struct stm_source_device *src,
 764                                struct stm_device *stm)
 765 {
 766         char *id;
 767         int err;
 768
 769         mutex_lock(&stm->link_mutex);
 770         spin_lock(&stm->link_lock);
 771         spin_lock(&src->link_lock);
 772
 773         /* src->link is dereferenced under stm_source_srcu but not the list */
 774         rcu_assign_pointer(src->link, stm);
 775         list_add_tail(&src->link_entry, &stm->link_list);
 776
 777         spin_unlock(&src->link_lock);
 778         spin_unlock(&stm->link_lock);
 779         mutex_unlock(&stm->link_mutex);
 780
 781         id = kstrdup(src->data->name, GFP_KERNEL);
 782         if (id) {
 783                 src->policy_node =
 784                         stp_policy_node_lookup(stm, id);
 785
 786                 kfree(id);
 787         }
 788
 789         err = stm_output_assign(stm, src->data->nr_chans,
 790                                 src->policy_node, &src->output);
 791
 792         if (src->policy_node)
 793                 stp_policy_node_put(src->policy_node);
 794
 795         if (err)
 796                 goto fail_detach;
 797
 798         /* this is to notify the STM device that a new link has been made */
 799         if (stm->data->link)
 800                 err = stm->data->link(stm->data, src->output.master,
 801                                       src->output.channel);
 802
 803         if (err)
 804                 goto fail_free_output;
 805
 806         /* this is to let the source carry out all necessary preparations */
 807         if (src->data->link)
 808                 src->data->link(src->data);
 809
 810         return 0;
 811
 812 fail_free_output:
 813         stm_output_free(stm, &src->output);
 814
 815 fail_detach:
 816         mutex_lock(&stm->link_mutex);
 817         spin_lock(&stm->link_lock);
 818         spin_lock(&src->link_lock);
 819
 820         rcu_assign_pointer(src->link, NULL);
 821         list_del_init(&src->link_entry);
 822
 823         spin_unlock(&src->link_lock);
 824         spin_unlock(&stm->link_lock);
 825         mutex_unlock(&stm->link_mutex);
 826
 827         return err;
 828 }
 829
 830 /**
 831  * __stm_source_link_drop() - detach stm_source from an stm device
 832  * @src:        stm_source device
 833  * @stm:        stm device
 834  *
 835  * If @stm is @src::link, disconnect them from one another and put the
 836  * reference on the @stm device.
 837  *
 838  * Caller must hold stm::link_mutex.
 839  */
 840 static int __stm_source_link_drop(struct stm_source_device *src,
 841                                   struct stm_device *stm)
 842 {
 843         struct stm_device *link;
 844         int ret = 0;
 845
 846         lockdep_assert_held(&stm->link_mutex);
 847
 848         /* for stm::link_list modification, we hold both mutex and spinlock */
 849         spin_lock(&stm->link_lock);
 850         spin_lock(&src->link_lock);
 851         link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
 852
 853         /*
 854          * The linked device may have changed since we last looked, because
 855          * we weren't holding the src::link_lock back then; if this is the
 856          * case, tell the caller to retry.
 857          */
 858         if (link != stm) {
 859                 ret = -EAGAIN;
 860                 goto unlock;
 861         }
 862
 863         stm_output_free(link, &src->output);
 864         list_del_init(&src->link_entry);
 865         /* matches stm_find_device() from stm_source_link_store() */
 866         stm_put_device(link);
 867         rcu_assign_pointer(src->link, NULL);
 868
 869 unlock:
 870         spin_unlock(&src->link_lock);
 871         spin_unlock(&stm->link_lock);
 872
 873         /*
 874          * Call the unlink callbacks for both source and stm, when we know
 875          * that we have actually performed the unlinking.
 876          */
 877         if (!ret) {
 878                 if (src->data->unlink)
 879                         src->data->unlink(src->data);
 880
 881                 if (stm->data->unlink)
 882                         stm->data->unlink(stm->data, src->output.master,
 883                                           src->output.channel);
 884         }
 885
 886         return ret;
 887 }
 888
 889 /**
 890  * stm_source_link_drop() - detach stm_source from its stm device
 891  * @src:        stm_source device
 892  *
 893  * Unlinking means disconnecting from source's STM device; after this
 894  * writes will be unsuccessful until it is linked to a new STM device.
 895  *
 896  * This will happen on "stm_source_link" sysfs attribute write to undo
 897  * the existing link (if any), or on linked STM device's de-registration.
 898  */
 899 static void stm_source_link_drop(struct stm_source_device *src)
 900 {
 901         struct stm_device *stm;
 902         int idx, ret;
 903
 904 retry:
 905         idx = srcu_read_lock(&stm_source_srcu);
 906         /*
 907          * The stm device will be valid for the duration of this
 908          * read section, but the link may change before we grab
 909          * the src::link_lock in __stm_source_link_drop().
 910          */
 911         stm = srcu_dereference(src->link, &stm_source_srcu);
 912
 913         ret = 0;
 914         if (stm) {
 915                 mutex_lock(&stm->link_mutex);
 916                 ret = __stm_source_link_drop(src, stm);
 917                 mutex_unlock(&stm->link_mutex);
 918         }
 919
 920         srcu_read_unlock(&stm_source_srcu, idx);
 921
 922         /* if it did change, retry */
 923         if (ret == -EAGAIN)
 924                 goto retry;
 925 }
 926
 927 static ssize_t stm_source_link_show(struct device *dev,
 928                                     struct device_attribute *attr,
 929                                     char *buf)
 930 {
 931         struct stm_source_device *src = to_stm_source_device(dev);
 932         struct stm_device *stm;
 933         int idx, ret;
 934
 935         idx = srcu_read_lock(&stm_source_srcu);
 936         stm = srcu_dereference(src->link, &stm_source_srcu);
 937         ret = sprintf(buf, "%s\n",
 938                       stm ? dev_name(&stm->dev) : "<none>");
 939         srcu_read_unlock(&stm_source_srcu, idx);
 940
 941         return ret;
 942 }
 943
 944 static ssize_t stm_source_link_store(struct device *dev,
 945                                      struct device_attribute *attr,
 946                                      const char *buf, size_t count)
 947 {
 948         struct stm_source_device *src = to_stm_source_device(dev);
 949         struct stm_device *link;
 950         int err;
 951
 952         stm_source_link_drop(src);
 953
 954         link = stm_find_device(buf);
 955         if (!link)
 956                 return -EINVAL;
 957
 958         err = stm_source_link_add(src, link);
 959         if (err) {
 960                 /* matches the stm_find_device() above */
 961                 stm_put_device(link);
 962         }
 963
 964         return err ? : count;
 965 }
 966
 967 static DEVICE_ATTR_RW(stm_source_link);
 968
 969 static struct attribute *stm_source_attrs[] = {
 970         &dev_attr_stm_source_link.attr,
 971         NULL,
 972 };
 973
 974 ATTRIBUTE_GROUPS(stm_source);
 975
 976 static struct class stm_source_class = {
 977         .name           = "stm_source",
 978         .dev_groups     = stm_source_groups,
 979 };
 980
 981 static void stm_source_device_release(struct device *dev)
 982 {
 983         struct stm_source_device *src = to_stm_source_device(dev);
 984
 985         kfree(src);
 986 }
 987
 988 /**
 989  * stm_source_register_device() - register an stm_source device
 990  * @parent:     parent device
 991  * @data:       device description structure
 992  *
 993  * This will create a device of stm_source class that can write
 994  * data to an stm device once linked.
 995  *
 996  * Return:      0 on success, -errno otherwise.
 997  */
 998 int stm_source_register_device(struct device *parent,
 999                                struct stm_source_data *data)
1000 {
1001         struct stm_source_device *src;
1002         int err;
1003
1004         if (!stm_core_up)
1005                 return -EPROBE_DEFER;
1006
1007         src = kzalloc(sizeof(*src), GFP_KERNEL);
1008         if (!src)
1009                 return -ENOMEM;
1010
1011         device_initialize(&src->dev);
1012         src->dev.class = &stm_source_class;
1013         src->dev.parent = parent;
1014         src->dev.release = stm_source_device_release;
1015
1016         err = kobject_set_name(&src->dev.kobj, "%s", data->name);
1017         if (err)
1018                 goto err;
1019
1020         err = device_add(&src->dev);
1021         if (err)
1022                 goto err;
1023
1024         stm_output_init(&src->output);
1025         spin_lock_init(&src->link_lock);
1026         INIT_LIST_HEAD(&src->link_entry);
1027         src->data = data;
1028         data->src = src;
1029
1030         return 0;
1031
1032 err:
1033         put_device(&src->dev);
1034         kfree(src);
1035
1036         return err;
1037 }
1038 EXPORT_SYMBOL_GPL(stm_source_register_device);
1039
1040 /**
1041  * stm_source_unregister_device() - unregister an stm_source device
1042  * @data:       device description that was used to register the device
1043  *
1044  * This will remove a previously created stm_source device from the system.
1045  */
1046 void stm_source_unregister_device(struct stm_source_data *data)
1047 {
1048         struct stm_source_device *src = data->src;
1049
1050         stm_source_link_drop(src);
1051
1052         device_destroy(&stm_source_class, src->dev.devt);
1053 }
1054 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
1055
1056 int stm_source_write(struct stm_source_data *data, unsigned int chan,
1057                      const char *buf, size_t count)
1058 {
1059         struct stm_source_device *src = data->src;
1060         struct stm_device *stm;
1061         int idx;
1062
1063         if (!src->output.nr_chans)
1064                 return -ENODEV;
1065
1066         if (chan >= src->output.nr_chans)
1067                 return -EINVAL;
1068
1069         idx = srcu_read_lock(&stm_source_srcu);
1070
1071         stm = srcu_dereference(src->link, &stm_source_srcu);
1072         if (stm)
1073                 count = stm_write(stm->data, src->output.master,
1074                                   src->output.channel + chan,
1075                                   buf, count);
1076         else
1077                 count = -ENODEV;
1078
1079         srcu_read_unlock(&stm_source_srcu, idx);
1080
1081         return count;
1082 }
1083 EXPORT_SYMBOL_GPL(stm_source_write);
1084
1085 static int __init stm_core_init(void)
1086 {
1087         int err;
1088
1089         err = class_register(&stm_class);
1090         if (err)
1091                 return err;
1092
1093         err = class_register(&stm_source_class);
1094         if (err)
1095                 goto err_stm;
1096
1097         err = stp_configfs_init();
1098         if (err)
1099                 goto err_src;
1100
1101         init_srcu_struct(&stm_source_srcu);
1102
1103         stm_core_up++;
1104
1105         return 0;
1106
1107 err_src:
1108         class_unregister(&stm_source_class);
1109 err_stm:
1110         class_unregister(&stm_class);
1111
1112         return err;
1113 }
1114
1115 module_init(stm_core_init);
1116
1117 static void __exit stm_core_exit(void)
1118 {
1119         cleanup_srcu_struct(&stm_source_srcu);
1120         class_unregister(&stm_source_class);
1121         class_unregister(&stm_class);
1122         stp_configfs_exit();
1123 }
1124
1125 module_exit(stm_core_exit);
1126
1127 MODULE_LICENSE("GPL v2");
1128 MODULE_DESCRIPTION("System Trace Module device class");
1129 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");