drivers/hwtracing/coresight/coresight-tmc-etf.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright(C) 2016 Linaro Limited. All rights reserved.
   4  * Author: Mathieu Poirier <mathieu.poirier@linaro.org>
   5  */
   6
   7 #include <linux/atomic.h>
   8 #include <linux/circ_buf.h>
   9 #include <linux/coresight.h>
  10 #include <linux/perf_event.h>
  11 #include <linux/slab.h>
  12 #include "coresight-priv.h"
  13 #include "coresight-tmc.h"
  14 #include "coresight-etm-perf.h"
  15
  16 static int tmc_set_etf_buffer(struct coresight_device *csdev,
  17                               struct perf_output_handle *handle);
  18
  19 static int __tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
  20 {
  21         int rc = 0;
  22
  23         CS_UNLOCK(drvdata->base);
  24
  25         /* Wait for TMCSReady bit to be set */
  26         rc = tmc_wait_for_tmcready(drvdata);
  27         if (rc) {
  28                 dev_err(&drvdata->csdev->dev,
  29                         "Failed to enable: TMC not ready\n");
  30                 CS_LOCK(drvdata->base);
  31                 return rc;
  32         }
  33
  34         writel_relaxed(TMC_MODE_CIRCULAR_BUFFER, drvdata->base + TMC_MODE);
  35         writel_relaxed(TMC_FFCR_EN_FMT | TMC_FFCR_EN_TI |
  36                        TMC_FFCR_FON_FLIN | TMC_FFCR_FON_TRIG_EVT |
  37                        TMC_FFCR_TRIGON_TRIGIN,
  38                        drvdata->base + TMC_FFCR);
  39
  40         writel_relaxed(drvdata->trigger_cntr, drvdata->base + TMC_TRG);
  41         tmc_enable_hw(drvdata);
  42
  43         CS_LOCK(drvdata->base);
  44         return rc;
  45 }
  46
  47 static int tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
  48 {
  49         int rc = coresight_claim_device(drvdata->csdev);
  50
  51         if (rc)
  52                 return rc;
  53
  54         rc = __tmc_etb_enable_hw(drvdata);
  55         if (rc)
  56                 coresight_disclaim_device(drvdata->csdev);
  57         return rc;
  58 }
  59
  60 static void tmc_etb_dump_hw(struct tmc_drvdata *drvdata)
  61 {
  62         char *bufp;
  63         u32 read_data, lost;
  64
  65         /* Check if the buffer wrapped around. */
  66         lost = readl_relaxed(drvdata->base + TMC_STS) & TMC_STS_FULL;
  67         bufp = drvdata->buf;
  68         drvdata->len = 0;
  69         while (1) {
  70                 read_data = readl_relaxed(drvdata->base + TMC_RRD);
  71                 if (read_data == 0xFFFFFFFF)
  72                         break;
  73                 memcpy(bufp, &read_data, 4);
  74                 bufp += 4;
  75                 drvdata->len += 4;
  76         }
  77
  78         if (lost)
  79                 coresight_insert_barrier_packet(drvdata->buf);
  80         return;
  81 }
  82
  83 static void __tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
  84 {
  85         CS_UNLOCK(drvdata->base);
  86
  87         tmc_flush_and_stop(drvdata);
  88         /*
  89          * When operating in sysFS mode the content of the buffer needs to be
  90          * read before the TMC is disabled.
  91          */
  92         if (drvdata->mode == CS_MODE_SYSFS)
  93                 tmc_etb_dump_hw(drvdata);
  94         tmc_disable_hw(drvdata);
  95
  96         CS_LOCK(drvdata->base);
  97 }
  98
  99 static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
 100 {
 101         __tmc_etb_disable_hw(drvdata);
 102         coresight_disclaim_device(drvdata->csdev);
 103 }
 104
 105 static int __tmc_etf_enable_hw(struct tmc_drvdata *drvdata)
 106 {
 107         int rc = 0;
 108
 109         CS_UNLOCK(drvdata->base);
 110
 111         /* Wait for TMCSReady bit to be set */
 112         rc = tmc_wait_for_tmcready(drvdata);
 113         if (rc) {
 114                 dev_err(&drvdata->csdev->dev,
 115                         "Failed to enable : TMC is not ready\n");
 116                 CS_LOCK(drvdata->base);
 117                 return rc;
 118         }
 119
 120         writel_relaxed(TMC_MODE_HARDWARE_FIFO, drvdata->base + TMC_MODE);
 121         writel_relaxed(TMC_FFCR_EN_FMT | TMC_FFCR_EN_TI,
 122                        drvdata->base + TMC_FFCR);
 123         writel_relaxed(0x0, drvdata->base + TMC_BUFWM);
 124         tmc_enable_hw(drvdata);
 125
 126         CS_LOCK(drvdata->base);
 127         return rc;
 128 }
 129
 130 static int tmc_etf_enable_hw(struct tmc_drvdata *drvdata)
 131 {
 132         int rc = coresight_claim_device(drvdata->csdev);
 133
 134         if (rc)
 135                 return rc;
 136
 137         rc = __tmc_etf_enable_hw(drvdata);
 138         if (rc)
 139                 coresight_disclaim_device(drvdata->csdev);
 140         return rc;
 141 }
 142
 143 static void tmc_etf_disable_hw(struct tmc_drvdata *drvdata)
 144 {
 145         struct coresight_device *csdev = drvdata->csdev;
 146
 147         CS_UNLOCK(drvdata->base);
 148
 149         tmc_flush_and_stop(drvdata);
 150         tmc_disable_hw(drvdata);
 151         coresight_disclaim_device_unlocked(csdev);
 152         CS_LOCK(drvdata->base);
 153 }
 154
 155 /*
 156  * Return the available trace data in the buffer from @pos, with
 157  * a maximum limit of @len, updating the @bufpp on where to
 158  * find it.
 159  */
 160 ssize_t tmc_etb_get_sysfs_trace(struct tmc_drvdata *drvdata,
 161                                 loff_t pos, size_t len, char **bufpp)
 162 {
 163         ssize_t actual = len;
 164
 165         /* Adjust the len to available size @pos */
 166         if (pos + actual > drvdata->len)
 167                 actual = drvdata->len - pos;
 168         if (actual > 0)
 169                 *bufpp = drvdata->buf + pos;
 170         return actual;
 171 }
 172
 173 static int tmc_enable_etf_sink_sysfs(struct coresight_device *csdev)
 174 {
 175         int ret = 0;
 176         bool used = false;
 177         char *buf = NULL;
 178         unsigned long flags;
 179         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 180
 181         /*
 182          * If we don't have a buffer release the lock and allocate memory.
 183          * Otherwise keep the lock and move along.
 184          */
 185         spin_lock_irqsave(&drvdata->spinlock, flags);
 186         if (!drvdata->buf) {
 187                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 188
 189                 /* Allocating the memory here while outside of the spinlock */
 190                 buf = kzalloc(drvdata->size, GFP_KERNEL);
 191                 if (!buf)
 192                         return -ENOMEM;
 193
 194                 /* Let's try again */
 195                 spin_lock_irqsave(&drvdata->spinlock, flags);
 196         }
 197
 198         if (drvdata->reading) {
 199                 ret = -EBUSY;
 200                 goto out;
 201         }
 202
 203         /*
 204          * In sysFS mode we can have multiple writers per sink.  Since this
 205          * sink is already enabled no memory is needed and the HW need not be
 206          * touched.
 207          */
 208         if (drvdata->mode == CS_MODE_SYSFS) {
 209                 atomic_inc(&csdev->refcnt);
 210                 goto out;
 211         }
 212
 213         /*
 214          * If drvdata::buf isn't NULL, memory was allocated for a previous
 215          * trace run but wasn't read.  If so simply zero-out the memory.
 216          * Otherwise use the memory allocated above.
 217          *
 218          * The memory is freed when users read the buffer using the
 219          * /dev/xyz.{etf|etb} interface.  See tmc_read_unprepare_etf() for
 220          * details.
 221          */
 222         if (drvdata->buf) {
 223                 memset(drvdata->buf, 0, drvdata->size);
 224         } else {
 225                 used = true;
 226                 drvdata->buf = buf;
 227         }
 228
 229         ret = tmc_etb_enable_hw(drvdata);
 230         if (!ret) {
 231                 drvdata->mode = CS_MODE_SYSFS;
 232                 atomic_inc(&csdev->refcnt);
 233         } else {
 234                 /* Free up the buffer if we failed to enable */
 235                 used = false;
 236         }
 237 out:
 238         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 239
 240         /* Free memory outside the spinlock if need be */
 241         if (!used)
 242                 kfree(buf);
 243
 244         return ret;
 245 }
 246
 247 static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data)
 248 {
 249         int ret = 0;
 250         pid_t pid;
 251         unsigned long flags;
 252         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 253         struct perf_output_handle *handle = data;
 254         struct cs_buffers *buf = etm_perf_sink_config(handle);
 255
 256         spin_lock_irqsave(&drvdata->spinlock, flags);
 257         do {
 258                 ret = -EINVAL;
 259                 if (drvdata->reading)
 260                         break;
 261                 /*
 262                  * No need to continue if the ETB/ETF is already operated
 263                  * from sysFS.
 264                  */
 265                 if (drvdata->mode == CS_MODE_SYSFS) {
 266                         ret = -EBUSY;
 267                         break;
 268                 }
 269
 270                 /* Get a handle on the pid of the process to monitor */
 271                 pid = buf->pid;
 272
 273                 if (drvdata->pid != -1 && drvdata->pid != pid) {
 274                         ret = -EBUSY;
 275                         break;
 276                 }
 277
 278                 ret = tmc_set_etf_buffer(csdev, handle);
 279                 if (ret)
 280                         break;
 281
 282                 /*
 283                  * No HW configuration is needed if the sink is already in
 284                  * use for this session.
 285                  */
 286                 if (drvdata->pid == pid) {
 287                         atomic_inc(&csdev->refcnt);
 288                         break;
 289                 }
 290
 291                 ret  = tmc_etb_enable_hw(drvdata);
 292                 if (!ret) {
 293                         /* Associate with monitored process. */
 294                         drvdata->pid = pid;
 295                         drvdata->mode = CS_MODE_PERF;
 296                         atomic_inc(&csdev->refcnt);
 297                 }
 298         } while (0);
 299         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 300
 301         return ret;
 302 }
 303
 304 static int tmc_enable_etf_sink(struct coresight_device *csdev,
 305                                enum cs_mode mode, void *data)
 306 {
 307         int ret;
 308
 309         switch (mode) {
 310         case CS_MODE_SYSFS:
 311                 ret = tmc_enable_etf_sink_sysfs(csdev);
 312                 break;
 313         case CS_MODE_PERF:
 314                 ret = tmc_enable_etf_sink_perf(csdev, data);
 315                 break;
 316         /* We shouldn't be here */
 317         default:
 318                 ret = -EINVAL;
 319                 break;
 320         }
 321
 322         if (ret)
 323                 return ret;
 324
 325         dev_dbg(&csdev->dev, "TMC-ETB/ETF enabled\n");
 326         return 0;
 327 }
 328
 329 static int tmc_disable_etf_sink(struct coresight_device *csdev)
 330 {
 331         unsigned long flags;
 332         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 333
 334         spin_lock_irqsave(&drvdata->spinlock, flags);
 335
 336         if (drvdata->reading) {
 337                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 338                 return -EBUSY;
 339         }
 340
 341         if (atomic_dec_return(&csdev->refcnt)) {
 342                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 343                 return -EBUSY;
 344         }
 345
 346         /* Complain if we (somehow) got out of sync */
 347         WARN_ON_ONCE(drvdata->mode == CS_MODE_DISABLED);
 348         tmc_etb_disable_hw(drvdata);
 349         /* Dissociate from monitored process. */
 350         drvdata->pid = -1;
 351         drvdata->mode = CS_MODE_DISABLED;
 352
 353         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 354
 355         dev_dbg(&csdev->dev, "TMC-ETB/ETF disabled\n");
 356         return 0;
 357 }
 358
 359 static int tmc_enable_etf_link(struct coresight_device *csdev,
 360                                struct coresight_connection *in,
 361                                struct coresight_connection *out)
 362 {
 363         int ret = 0;
 364         unsigned long flags;
 365         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 366         bool first_enable = false;
 367
 368         spin_lock_irqsave(&drvdata->spinlock, flags);
 369         if (drvdata->reading) {
 370                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 371                 return -EBUSY;
 372         }
 373
 374         if (atomic_read(&csdev->refcnt) == 0) {
 375                 ret = tmc_etf_enable_hw(drvdata);
 376                 if (!ret) {
 377                         drvdata->mode = CS_MODE_SYSFS;
 378                         first_enable = true;
 379                 }
 380         }
 381         if (!ret)
 382                 atomic_inc(&csdev->refcnt);
 383         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 384
 385         if (first_enable)
 386                 dev_dbg(&csdev->dev, "TMC-ETF enabled\n");
 387         return ret;
 388 }
 389
 390 static void tmc_disable_etf_link(struct coresight_device *csdev,
 391                                  struct coresight_connection *in,
 392                                  struct coresight_connection *out)
 393 {
 394         unsigned long flags;
 395         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 396         bool last_disable = false;
 397
 398         spin_lock_irqsave(&drvdata->spinlock, flags);
 399         if (drvdata->reading) {
 400                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 401                 return;
 402         }
 403
 404         if (atomic_dec_return(&csdev->refcnt) == 0) {
 405                 tmc_etf_disable_hw(drvdata);
 406                 drvdata->mode = CS_MODE_DISABLED;
 407                 last_disable = true;
 408         }
 409         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 410
 411         if (last_disable)
 412                 dev_dbg(&csdev->dev, "TMC-ETF disabled\n");
 413 }
 414
 415 static void *tmc_alloc_etf_buffer(struct coresight_device *csdev,
 416                                   struct perf_event *event, void **pages,
 417                                   int nr_pages, bool overwrite)
 418 {
 419         int node;
 420         struct cs_buffers *buf;
 421
 422         node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
 423
 424         /* Allocate memory structure for interaction with Perf */
 425         buf = kzalloc_node(sizeof(struct cs_buffers), GFP_KERNEL, node);
 426         if (!buf)
 427                 return NULL;
 428
 429         buf->pid = task_pid_nr(event->owner);
 430         buf->snapshot = overwrite;
 431         buf->nr_pages = nr_pages;
 432         buf->data_pages = pages;
 433
 434         return buf;
 435 }
 436
 437 static void tmc_free_etf_buffer(void *config)
 438 {
 439         struct cs_buffers *buf = config;
 440
 441         kfree(buf);
 442 }
 443
 444 static int tmc_set_etf_buffer(struct coresight_device *csdev,
 445                               struct perf_output_handle *handle)
 446 {
 447         int ret = 0;
 448         unsigned long head;
 449         struct cs_buffers *buf = etm_perf_sink_config(handle);
 450
 451         if (!buf)
 452                 return -EINVAL;
 453
 454         /* wrap head around to the amount of space we have */
 455         head = handle->head & (((unsigned long)buf->nr_pages << PAGE_SHIFT) - 1);
 456
 457         /* find the page to write to */
 458         buf->cur = head / PAGE_SIZE;
 459
 460         /* and offset within that page */
 461         buf->offset = head % PAGE_SIZE;
 462
 463         local_set(&buf->data_size, 0);
 464
 465         return ret;
 466 }
 467
 468 static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
 469                                   struct perf_output_handle *handle,
 470                                   void *sink_config)
 471 {
 472         bool lost = false;
 473         int i, cur;
 474         const u32 *barrier;
 475         u32 *buf_ptr;
 476         u64 read_ptr, write_ptr;
 477         u32 status;
 478         unsigned long offset, to_read = 0, flags;
 479         struct cs_buffers *buf = sink_config;
 480         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 481
 482         if (!buf)
 483                 return 0;
 484
 485         /* This shouldn't happen */
 486         if (WARN_ON_ONCE(drvdata->mode != CS_MODE_PERF))
 487                 return 0;
 488
 489         spin_lock_irqsave(&drvdata->spinlock, flags);
 490
 491         /* Don't do anything if another tracer is using this sink */
 492         if (atomic_read(&csdev->refcnt) != 1)
 493                 goto out;
 494
 495         CS_UNLOCK(drvdata->base);
 496
 497         tmc_flush_and_stop(drvdata);
 498
 499         read_ptr = tmc_read_rrp(drvdata);
 500         write_ptr = tmc_read_rwp(drvdata);
 501
 502         /*
 503          * Get a hold of the status register and see if a wrap around
 504          * has occurred.  If so adjust things accordingly.
 505          */
 506         status = readl_relaxed(drvdata->base + TMC_STS);
 507         if (status & TMC_STS_FULL) {
 508                 lost = true;
 509                 to_read = drvdata->size;
 510         } else {
 511                 to_read = CIRC_CNT(write_ptr, read_ptr, drvdata->size);
 512         }
 513
 514         /*
 515          * The TMC RAM buffer may be bigger than the space available in the
 516          * perf ring buffer (handle->size).  If so advance the RRP so that we
 517          * get the latest trace data.  In snapshot mode none of that matters
 518          * since we are expected to clobber stale data in favour of the latest
 519          * traces.
 520          */
 521         if (!buf->snapshot && to_read > handle->size) {
 522                 u32 mask = tmc_get_memwidth_mask(drvdata);
 523
 524                 /*
 525                  * Make sure the new size is aligned in accordance with the
 526                  * requirement explained in function tmc_get_memwidth_mask().
 527                  */
 528                 to_read = handle->size & mask;
 529                 /* Move the RAM read pointer up */
 530                 read_ptr = (write_ptr + drvdata->size) - to_read;
 531                 /* Make sure we are still within our limits */
 532                 if (read_ptr > (drvdata->size - 1))
 533                         read_ptr -= drvdata->size;
 534                 /* Tell the HW */
 535                 tmc_write_rrp(drvdata, read_ptr);
 536                 lost = true;
 537         }
 538
 539         /*
 540          * Don't set the TRUNCATED flag in snapshot mode because 1) the
 541          * captured buffer is expected to be truncated and 2) a full buffer
 542          * prevents the event from being re-enabled by the perf core,
 543          * resulting in stale data being send to user space.
 544          */
 545         if (!buf->snapshot && lost)
 546                 perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
 547
 548         cur = buf->cur;
 549         offset = buf->offset;
 550         barrier = coresight_barrier_pkt;
 551
 552         /* for every byte to read */
 553         for (i = 0; i < to_read; i += 4) {
 554                 buf_ptr = buf->data_pages[cur] + offset;
 555                 *buf_ptr = readl_relaxed(drvdata->base + TMC_RRD);
 556
 557                 if (lost && i < CORESIGHT_BARRIER_PKT_SIZE) {
 558                         *buf_ptr = *barrier;
 559                         barrier++;
 560                 }
 561
 562                 offset += 4;
 563                 if (offset >= PAGE_SIZE) {
 564                         offset = 0;
 565                         cur++;
 566                         /* wrap around at the end of the buffer */
 567                         cur &= buf->nr_pages - 1;
 568                 }
 569         }
 570
 571         /*
 572          * In snapshot mode we simply increment the head by the number of byte
 573          * that were written.  User space will figure out how many bytes to get
 574          * from the AUX buffer based on the position of the head.
 575          */
 576         if (buf->snapshot)
 577                 handle->head += to_read;
 578
 579         /*
 580          * CS_LOCK() contains mb() so it can ensure visibility of the AUX trace
 581          * data before the aux_head is updated via perf_aux_output_end(), which
 582          * is expected by the perf ring buffer.
 583          */
 584         CS_LOCK(drvdata->base);
 585 out:
 586         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 587
 588         return to_read;
 589 }
 590
 591 static const struct coresight_ops_sink tmc_etf_sink_ops = {
 592         .enable         = tmc_enable_etf_sink,
 593         .disable        = tmc_disable_etf_sink,
 594         .alloc_buffer   = tmc_alloc_etf_buffer,
 595         .free_buffer    = tmc_free_etf_buffer,
 596         .update_buffer  = tmc_update_etf_buffer,
 597 };
 598
 599 static const struct coresight_ops_link tmc_etf_link_ops = {
 600         .enable         = tmc_enable_etf_link,
 601         .disable        = tmc_disable_etf_link,
 602 };
 603
 604 const struct coresight_ops tmc_etb_cs_ops = {
 605         .sink_ops       = &tmc_etf_sink_ops,
 606 };
 607
 608 const struct coresight_ops tmc_etf_cs_ops = {
 609         .sink_ops       = &tmc_etf_sink_ops,
 610         .link_ops       = &tmc_etf_link_ops,
 611 };
 612
 613 int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
 614 {
 615         enum tmc_mode mode;
 616         int ret = 0;
 617         unsigned long flags;
 618
 619         /* config types are set a boot time and never change */
 620         if (WARN_ON_ONCE(drvdata->config_type != TMC_CONFIG_TYPE_ETB &&
 621                          drvdata->config_type != TMC_CONFIG_TYPE_ETF))
 622                 return -EINVAL;
 623
 624         spin_lock_irqsave(&drvdata->spinlock, flags);
 625
 626         if (drvdata->reading) {
 627                 ret = -EBUSY;
 628                 goto out;
 629         }
 630
 631         /* Don't interfere if operated from Perf */
 632         if (drvdata->mode == CS_MODE_PERF) {
 633                 ret = -EINVAL;
 634                 goto out;
 635         }
 636
 637         /* If drvdata::buf is NULL the trace data has been read already */
 638         if (drvdata->buf == NULL) {
 639                 ret = -EINVAL;
 640                 goto out;
 641         }
 642
 643         /* Disable the TMC if need be */
 644         if (drvdata->mode == CS_MODE_SYSFS) {
 645                 /* There is no point in reading a TMC in HW FIFO mode */
 646                 mode = readl_relaxed(drvdata->base + TMC_MODE);
 647                 if (mode != TMC_MODE_CIRCULAR_BUFFER) {
 648                         ret = -EINVAL;
 649                         goto out;
 650                 }
 651                 __tmc_etb_disable_hw(drvdata);
 652         }
 653
 654         drvdata->reading = true;
 655 out:
 656         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 657
 658         return ret;
 659 }
 660
 661 int tmc_read_unprepare_etb(struct tmc_drvdata *drvdata)
 662 {
 663         char *buf = NULL;
 664         enum tmc_mode mode;
 665         unsigned long flags;
 666         int rc = 0;
 667
 668         /* config types are set a boot time and never change */
 669         if (WARN_ON_ONCE(drvdata->config_type != TMC_CONFIG_TYPE_ETB &&
 670                          drvdata->config_type != TMC_CONFIG_TYPE_ETF))
 671                 return -EINVAL;
 672
 673         spin_lock_irqsave(&drvdata->spinlock, flags);
 674
 675         /* Re-enable the TMC if need be */
 676         if (drvdata->mode == CS_MODE_SYSFS) {
 677                 /* There is no point in reading a TMC in HW FIFO mode */
 678                 mode = readl_relaxed(drvdata->base + TMC_MODE);
 679                 if (mode != TMC_MODE_CIRCULAR_BUFFER) {
 680                         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 681                         return -EINVAL;
 682                 }
 683                 /*
 684                  * The trace run will continue with the same allocated trace
 685                  * buffer. As such zero-out the buffer so that we don't end
 686                  * up with stale data.
 687                  *
 688                  * Since the tracer is still enabled drvdata::buf
 689                  * can't be NULL.
 690                  */
 691                 memset(drvdata->buf, 0, drvdata->size);
 692                 rc = __tmc_etb_enable_hw(drvdata);
 693                 if (rc) {
 694                         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 695                         return rc;
 696                 }
 697         } else {
 698                 /*
 699                  * The ETB/ETF is not tracing and the buffer was just read.
 700                  * As such prepare to free the trace buffer.
 701                  */
 702                 buf = drvdata->buf;
 703                 drvdata->buf = NULL;
 704         }
 705
 706         drvdata->reading = false;
 707         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 708
 709         /*
 710          * Free allocated memory outside of the spinlock.  There is no need
 711          * to assert the validity of 'buf' since calling kfree(NULL) is safe.
 712          */
 713         kfree(buf);
 714
 715         return 0;
 716 }