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