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 void __tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
  20 {
  21         CS_UNLOCK(drvdata->base);
  22
  23         /* Wait for TMCSReady bit to be set */
  24         tmc_wait_for_tmcready(drvdata);
  25
  26         writel_relaxed(TMC_MODE_CIRCULAR_BUFFER, drvdata->base + TMC_MODE);
  27         writel_relaxed(TMC_FFCR_EN_FMT | TMC_FFCR_EN_TI |
  28                        TMC_FFCR_FON_FLIN | TMC_FFCR_FON_TRIG_EVT |
  29                        TMC_FFCR_TRIGON_TRIGIN,
  30                        drvdata->base + TMC_FFCR);
  31
  32         writel_relaxed(drvdata->trigger_cntr, drvdata->base + TMC_TRG);
  33         tmc_enable_hw(drvdata);
  34
  35         CS_LOCK(drvdata->base);
  36 }
  37
  38 static int tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
  39 {
  40         int rc = coresight_claim_device(drvdata->base);
  41
  42         if (rc)
  43                 return rc;
  44
  45         __tmc_etb_enable_hw(drvdata);
  46         return 0;
  47 }
  48
  49 static void tmc_etb_dump_hw(struct tmc_drvdata *drvdata)
  50 {
  51         char *bufp;
  52         u32 read_data, lost;
  53
  54         /* Check if the buffer wrapped around. */
  55         lost = readl_relaxed(drvdata->base + TMC_STS) & TMC_STS_FULL;
  56         bufp = drvdata->buf;
  57         drvdata->len = 0;
  58         while (1) {
  59                 read_data = readl_relaxed(drvdata->base + TMC_RRD);
  60                 if (read_data == 0xFFFFFFFF)
  61                         break;
  62                 memcpy(bufp, &read_data, 4);
  63                 bufp += 4;
  64                 drvdata->len += 4;
  65         }
  66
  67         if (lost)
  68                 coresight_insert_barrier_packet(drvdata->buf);
  69         return;
  70 }
  71
  72 static void __tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
  73 {
  74         CS_UNLOCK(drvdata->base);
  75
  76         tmc_flush_and_stop(drvdata);
  77         /*
  78          * When operating in sysFS mode the content of the buffer needs to be
  79          * read before the TMC is disabled.
  80          */
  81         if (drvdata->mode == CS_MODE_SYSFS)
  82                 tmc_etb_dump_hw(drvdata);
  83         tmc_disable_hw(drvdata);
  84
  85         CS_LOCK(drvdata->base);
  86 }
  87
  88 static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
  89 {
  90         __tmc_etb_disable_hw(drvdata);
  91         coresight_disclaim_device(drvdata->base);
  92 }
  93
  94 static void __tmc_etf_enable_hw(struct tmc_drvdata *drvdata)
  95 {
  96         CS_UNLOCK(drvdata->base);
  97
  98         /* Wait for TMCSReady bit to be set */
  99         tmc_wait_for_tmcready(drvdata);
 100
 101         writel_relaxed(TMC_MODE_HARDWARE_FIFO, drvdata->base + TMC_MODE);
 102         writel_relaxed(TMC_FFCR_EN_FMT | TMC_FFCR_EN_TI,
 103                        drvdata->base + TMC_FFCR);
 104         writel_relaxed(0x0, drvdata->base + TMC_BUFWM);
 105         tmc_enable_hw(drvdata);
 106
 107         CS_LOCK(drvdata->base);
 108 }
 109
 110 static int tmc_etf_enable_hw(struct tmc_drvdata *drvdata)
 111 {
 112         int rc = coresight_claim_device(drvdata->base);
 113
 114         if (rc)
 115                 return rc;
 116
 117         __tmc_etf_enable_hw(drvdata);
 118         return 0;
 119 }
 120
 121 static void tmc_etf_disable_hw(struct tmc_drvdata *drvdata)
 122 {
 123         CS_UNLOCK(drvdata->base);
 124
 125         tmc_flush_and_stop(drvdata);
 126         tmc_disable_hw(drvdata);
 127         coresight_disclaim_device_unlocked(drvdata->base);
 128         CS_LOCK(drvdata->base);
 129 }
 130
 131 /*
 132  * Return the available trace data in the buffer from @pos, with
 133  * a maximum limit of @len, updating the @bufpp on where to
 134  * find it.
 135  */
 136 ssize_t tmc_etb_get_sysfs_trace(struct tmc_drvdata *drvdata,
 137                                 loff_t pos, size_t len, char **bufpp)
 138 {
 139         ssize_t actual = len;
 140
 141         /* Adjust the len to available size @pos */
 142         if (pos + actual > drvdata->len)
 143                 actual = drvdata->len - pos;
 144         if (actual > 0)
 145                 *bufpp = drvdata->buf + pos;
 146         return actual;
 147 }
 148
 149 static int tmc_enable_etf_sink_sysfs(struct coresight_device *csdev)
 150 {
 151         int ret = 0;
 152         bool used = false;
 153         char *buf = NULL;
 154         unsigned long flags;
 155         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 156
 157         /*
 158          * If we don't have a buffer release the lock and allocate memory.
 159          * Otherwise keep the lock and move along.
 160          */
 161         spin_lock_irqsave(&drvdata->spinlock, flags);
 162         if (!drvdata->buf) {
 163                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 164
 165                 /* Allocating the memory here while outside of the spinlock */
 166                 buf = kzalloc(drvdata->size, GFP_KERNEL);
 167                 if (!buf)
 168                         return -ENOMEM;
 169
 170                 /* Let's try again */
 171                 spin_lock_irqsave(&drvdata->spinlock, flags);
 172         }
 173
 174         if (drvdata->reading) {
 175                 ret = -EBUSY;
 176                 goto out;
 177         }
 178
 179         /*
 180          * In sysFS mode we can have multiple writers per sink.  Since this
 181          * sink is already enabled no memory is needed and the HW need not be
 182          * touched.
 183          */
 184         if (drvdata->mode == CS_MODE_SYSFS) {
 185                 atomic_inc(csdev->refcnt);
 186                 goto out;
 187         }
 188
 189         /*
 190          * If drvdata::buf isn't NULL, memory was allocated for a previous
 191          * trace run but wasn't read.  If so simply zero-out the memory.
 192          * Otherwise use the memory allocated above.
 193          *
 194          * The memory is freed when users read the buffer using the
 195          * /dev/xyz.{etf|etb} interface.  See tmc_read_unprepare_etf() for
 196          * details.
 197          */
 198         if (drvdata->buf) {
 199                 memset(drvdata->buf, 0, drvdata->size);
 200         } else {
 201                 used = true;
 202                 drvdata->buf = buf;
 203         }
 204
 205         ret = tmc_etb_enable_hw(drvdata);
 206         if (!ret) {
 207                 drvdata->mode = CS_MODE_SYSFS;
 208                 atomic_inc(csdev->refcnt);
 209         } else {
 210                 /* Free up the buffer if we failed to enable */
 211                 used = false;
 212         }
 213 out:
 214         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 215
 216         /* Free memory outside the spinlock if need be */
 217         if (!used)
 218                 kfree(buf);
 219
 220         return ret;
 221 }
 222
 223 static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data)
 224 {
 225         int ret = 0;
 226         pid_t pid;
 227         unsigned long flags;
 228         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 229         struct perf_output_handle *handle = data;
 230
 231         spin_lock_irqsave(&drvdata->spinlock, flags);
 232         do {
 233                 ret = -EINVAL;
 234                 if (drvdata->reading)
 235                         break;
 236                 /*
 237                  * No need to continue if the ETB/ETF is already operated
 238                  * from sysFS.
 239                  */
 240                 if (drvdata->mode == CS_MODE_SYSFS) {
 241                         ret = -EBUSY;
 242                         break;
 243                 }
 244
 245                 /* Get a handle on the pid of the process to monitor */
 246                 pid = task_pid_nr(handle->event->owner);
 247
 248                 if (drvdata->pid != -1 && drvdata->pid != pid) {
 249                         ret = -EBUSY;
 250                         break;
 251                 }
 252
 253                 ret = tmc_set_etf_buffer(csdev, handle);
 254                 if (ret)
 255                         break;
 256
 257                 /*
 258                  * No HW configuration is needed if the sink is already in
 259                  * use for this session.
 260                  */
 261                 if (drvdata->pid == pid) {
 262                         atomic_inc(csdev->refcnt);
 263                         break;
 264                 }
 265
 266                 ret  = tmc_etb_enable_hw(drvdata);
 267                 if (!ret) {
 268                         /* Associate with monitored process. */
 269                         drvdata->pid = pid;
 270                         drvdata->mode = CS_MODE_PERF;
 271                         atomic_inc(csdev->refcnt);
 272                 }
 273         } while (0);
 274         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 275
 276         return ret;
 277 }
 278
 279 static int tmc_enable_etf_sink(struct coresight_device *csdev,
 280                                u32 mode, void *data)
 281 {
 282         int ret;
 283
 284         switch (mode) {
 285         case CS_MODE_SYSFS:
 286                 ret = tmc_enable_etf_sink_sysfs(csdev);
 287                 break;
 288         case CS_MODE_PERF:
 289                 ret = tmc_enable_etf_sink_perf(csdev, data);
 290                 break;
 291         /* We shouldn't be here */
 292         default:
 293                 ret = -EINVAL;
 294                 break;
 295         }
 296
 297         if (ret)
 298                 return ret;
 299
 300         dev_dbg(&csdev->dev, "TMC-ETB/ETF enabled\n");
 301         return 0;
 302 }
 303
 304 static int tmc_disable_etf_sink(struct coresight_device *csdev)
 305 {
 306         unsigned long flags;
 307         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 308
 309         spin_lock_irqsave(&drvdata->spinlock, flags);
 310
 311         if (drvdata->reading) {
 312                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 313                 return -EBUSY;
 314         }
 315
 316         if (atomic_dec_return(csdev->refcnt)) {
 317                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 318                 return -EBUSY;
 319         }
 320
 321         /* Complain if we (somehow) got out of sync */
 322         WARN_ON_ONCE(drvdata->mode == CS_MODE_DISABLED);
 323         tmc_etb_disable_hw(drvdata);
 324         /* Dissociate from monitored process. */
 325         drvdata->pid = -1;
 326         drvdata->mode = CS_MODE_DISABLED;
 327
 328         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 329
 330         dev_dbg(&csdev->dev, "TMC-ETB/ETF disabled\n");
 331         return 0;
 332 }
 333
 334 static int tmc_enable_etf_link(struct coresight_device *csdev,
 335                                int inport, int outport)
 336 {
 337         int ret;
 338         unsigned long flags;
 339         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 340
 341         spin_lock_irqsave(&drvdata->spinlock, flags);
 342         if (drvdata->reading) {
 343                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 344                 return -EBUSY;
 345         }
 346
 347         ret = tmc_etf_enable_hw(drvdata);
 348         if (!ret)
 349                 drvdata->mode = CS_MODE_SYSFS;
 350         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 351
 352         if (!ret)
 353                 dev_dbg(&csdev->dev, "TMC-ETF enabled\n");
 354         return ret;
 355 }
 356
 357 static void tmc_disable_etf_link(struct coresight_device *csdev,
 358                                  int inport, int outport)
 359 {
 360         unsigned long flags;
 361         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 362
 363         spin_lock_irqsave(&drvdata->spinlock, flags);
 364         if (drvdata->reading) {
 365                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 366                 return;
 367         }
 368
 369         tmc_etf_disable_hw(drvdata);
 370         drvdata->mode = CS_MODE_DISABLED;
 371         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 372
 373         dev_dbg(&csdev->dev, "TMC-ETF disabled\n");
 374 }
 375
 376 static void *tmc_alloc_etf_buffer(struct coresight_device *csdev,
 377                                   struct perf_event *event, void **pages,
 378                                   int nr_pages, bool overwrite)
 379 {
 380         int node;
 381         struct cs_buffers *buf;
 382
 383         node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
 384
 385         /* Allocate memory structure for interaction with Perf */
 386         buf = kzalloc_node(sizeof(struct cs_buffers), GFP_KERNEL, node);
 387         if (!buf)
 388                 return NULL;
 389
 390         buf->snapshot = overwrite;
 391         buf->nr_pages = nr_pages;
 392         buf->data_pages = pages;
 393
 394         return buf;
 395 }
 396
 397 static void tmc_free_etf_buffer(void *config)
 398 {
 399         struct cs_buffers *buf = config;
 400
 401         kfree(buf);
 402 }
 403
 404 static int tmc_set_etf_buffer(struct coresight_device *csdev,
 405                               struct perf_output_handle *handle)
 406 {
 407         int ret = 0;
 408         unsigned long head;
 409         struct cs_buffers *buf = etm_perf_sink_config(handle);
 410
 411         if (!buf)
 412                 return -EINVAL;
 413
 414         /* wrap head around to the amount of space we have */
 415         head = handle->head & ((buf->nr_pages << PAGE_SHIFT) - 1);
 416
 417         /* find the page to write to */
 418         buf->cur = head / PAGE_SIZE;
 419
 420         /* and offset within that page */
 421         buf->offset = head % PAGE_SIZE;
 422
 423         local_set(&buf->data_size, 0);
 424
 425         return ret;
 426 }
 427
 428 static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
 429                                   struct perf_output_handle *handle,
 430                                   void *sink_config)
 431 {
 432         bool lost = false;
 433         int i, cur;
 434         const u32 *barrier;
 435         u32 *buf_ptr;
 436         u64 read_ptr, write_ptr;
 437         u32 status;
 438         unsigned long offset, to_read = 0, flags;
 439         struct cs_buffers *buf = sink_config;
 440         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 441
 442         if (!buf)
 443                 return 0;
 444
 445         /* This shouldn't happen */
 446         if (WARN_ON_ONCE(drvdata->mode != CS_MODE_PERF))
 447                 return 0;
 448
 449         spin_lock_irqsave(&drvdata->spinlock, flags);
 450
 451         /* Don't do anything if another tracer is using this sink */
 452         if (atomic_read(csdev->refcnt) != 1)
 453                 goto out;
 454
 455         CS_UNLOCK(drvdata->base);
 456
 457         tmc_flush_and_stop(drvdata);
 458
 459         read_ptr = tmc_read_rrp(drvdata);
 460         write_ptr = tmc_read_rwp(drvdata);
 461
 462         /*
 463          * Get a hold of the status register and see if a wrap around
 464          * has occurred.  If so adjust things accordingly.
 465          */
 466         status = readl_relaxed(drvdata->base + TMC_STS);
 467         if (status & TMC_STS_FULL) {
 468                 lost = true;
 469                 to_read = drvdata->size;
 470         } else {
 471                 to_read = CIRC_CNT(write_ptr, read_ptr, drvdata->size);
 472         }
 473
 474         /*
 475          * The TMC RAM buffer may be bigger than the space available in the
 476          * perf ring buffer (handle->size).  If so advance the RRP so that we
 477          * get the latest trace data.  In snapshot mode none of that matters
 478          * since we are expected to clobber stale data in favour of the latest
 479          * traces.
 480          */
 481         if (!buf->snapshot && to_read > handle->size) {
 482                 u32 mask = 0;
 483
 484                 /*
 485                  * The value written to RRP must be byte-address aligned to
 486                  * the width of the trace memory databus _and_ to a frame
 487                  * boundary (16 byte), whichever is the biggest. For example,
 488                  * for 32-bit, 64-bit and 128-bit wide trace memory, the four
 489                  * LSBs must be 0s. For 256-bit wide trace memory, the five
 490                  * LSBs must be 0s.
 491                  */
 492                 switch (drvdata->memwidth) {
 493                 case TMC_MEM_INTF_WIDTH_32BITS:
 494                 case TMC_MEM_INTF_WIDTH_64BITS:
 495                 case TMC_MEM_INTF_WIDTH_128BITS:
 496                         mask = GENMASK(31, 4);
 497                         break;
 498                 case TMC_MEM_INTF_WIDTH_256BITS:
 499                         mask = GENMASK(31, 5);
 500                         break;
 501                 }
 502
 503                 /*
 504                  * Make sure the new size is aligned in accordance with the
 505                  * requirement explained above.
 506                  */
 507                 to_read = handle->size & mask;
 508                 /* Move the RAM read pointer up */
 509                 read_ptr = (write_ptr + drvdata->size) - to_read;
 510                 /* Make sure we are still within our limits */
 511                 if (read_ptr > (drvdata->size - 1))
 512                         read_ptr -= drvdata->size;
 513                 /* Tell the HW */
 514                 tmc_write_rrp(drvdata, read_ptr);
 515                 lost = true;
 516         }
 517
 518         /*
 519          * Don't set the TRUNCATED flag in snapshot mode because 1) the
 520          * captured buffer is expected to be truncated and 2) a full buffer
 521          * prevents the event from being re-enabled by the perf core,
 522          * resulting in stale data being send to user space.
 523          */
 524         if (!buf->snapshot && lost)
 525                 perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);
 526
 527         cur = buf->cur;
 528         offset = buf->offset;
 529         barrier = barrier_pkt;
 530
 531         /* for every byte to read */
 532         for (i = 0; i < to_read; i += 4) {
 533                 buf_ptr = buf->data_pages[cur] + offset;
 534                 *buf_ptr = readl_relaxed(drvdata->base + TMC_RRD);
 535
 536                 if (lost && *barrier) {
 537                         *buf_ptr = *barrier;
 538                         barrier++;
 539                 }
 540
 541                 offset += 4;
 542                 if (offset >= PAGE_SIZE) {
 543                         offset = 0;
 544                         cur++;
 545                         /* wrap around at the end of the buffer */
 546                         cur &= buf->nr_pages - 1;
 547                 }
 548         }
 549
 550         /*
 551          * In snapshot mode we simply increment the head by the number of byte
 552          * that were written.  User space function  cs_etm_find_snapshot() will
 553          * figure out how many bytes to get from the AUX buffer based on the
 554          * position of the head.
 555          */
 556         if (buf->snapshot)
 557                 handle->head += to_read;
 558
 559         CS_LOCK(drvdata->base);
 560 out:
 561         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 562
 563         return to_read;
 564 }
 565
 566 static const struct coresight_ops_sink tmc_etf_sink_ops = {
 567         .enable         = tmc_enable_etf_sink,
 568         .disable        = tmc_disable_etf_sink,
 569         .alloc_buffer   = tmc_alloc_etf_buffer,
 570         .free_buffer    = tmc_free_etf_buffer,
 571         .update_buffer  = tmc_update_etf_buffer,
 572 };
 573
 574 static const struct coresight_ops_link tmc_etf_link_ops = {
 575         .enable         = tmc_enable_etf_link,
 576         .disable        = tmc_disable_etf_link,
 577 };
 578
 579 const struct coresight_ops tmc_etb_cs_ops = {
 580         .sink_ops       = &tmc_etf_sink_ops,
 581 };
 582
 583 const struct coresight_ops tmc_etf_cs_ops = {
 584         .sink_ops       = &tmc_etf_sink_ops,
 585         .link_ops       = &tmc_etf_link_ops,
 586 };
 587
 588 int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
 589 {
 590         enum tmc_mode mode;
 591         int ret = 0;
 592         unsigned long flags;
 593
 594         /* config types are set a boot time and never change */
 595         if (WARN_ON_ONCE(drvdata->config_type != TMC_CONFIG_TYPE_ETB &&
 596                          drvdata->config_type != TMC_CONFIG_TYPE_ETF))
 597                 return -EINVAL;
 598
 599         spin_lock_irqsave(&drvdata->spinlock, flags);
 600
 601         if (drvdata->reading) {
 602                 ret = -EBUSY;
 603                 goto out;
 604         }
 605
 606         /* There is no point in reading a TMC in HW FIFO mode */
 607         mode = readl_relaxed(drvdata->base + TMC_MODE);
 608         if (mode != TMC_MODE_CIRCULAR_BUFFER) {
 609                 ret = -EINVAL;
 610                 goto out;
 611         }
 612
 613         /* Don't interfere if operated from Perf */
 614         if (drvdata->mode == CS_MODE_PERF) {
 615                 ret = -EINVAL;
 616                 goto out;
 617         }
 618
 619         /* If drvdata::buf is NULL the trace data has been read already */
 620         if (drvdata->buf == NULL) {
 621                 ret = -EINVAL;
 622                 goto out;
 623         }
 624
 625         /* Disable the TMC if need be */
 626         if (drvdata->mode == CS_MODE_SYSFS)
 627                 __tmc_etb_disable_hw(drvdata);
 628
 629         drvdata->reading = true;
 630 out:
 631         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 632
 633         return ret;
 634 }
 635
 636 int tmc_read_unprepare_etb(struct tmc_drvdata *drvdata)
 637 {
 638         char *buf = NULL;
 639         enum tmc_mode mode;
 640         unsigned long flags;
 641
 642         /* config types are set a boot time and never change */
 643         if (WARN_ON_ONCE(drvdata->config_type != TMC_CONFIG_TYPE_ETB &&
 644                          drvdata->config_type != TMC_CONFIG_TYPE_ETF))
 645                 return -EINVAL;
 646
 647         spin_lock_irqsave(&drvdata->spinlock, flags);
 648
 649         /* There is no point in reading a TMC in HW FIFO mode */
 650         mode = readl_relaxed(drvdata->base + TMC_MODE);
 651         if (mode != TMC_MODE_CIRCULAR_BUFFER) {
 652                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
 653                 return -EINVAL;
 654         }
 655
 656         /* Re-enable the TMC if need be */
 657         if (drvdata->mode == CS_MODE_SYSFS) {
 658                 /*
 659                  * The trace run will continue with the same allocated trace
 660                  * buffer. As such zero-out the buffer so that we don't end
 661                  * up with stale data.
 662                  *
 663                  * Since the tracer is still enabled drvdata::buf
 664                  * can't be NULL.
 665                  */
 666                 memset(drvdata->buf, 0, drvdata->size);
 667                 __tmc_etb_enable_hw(drvdata);
 668         } else {
 669                 /*
 670                  * The ETB/ETF is not tracing and the buffer was just read.
 671                  * As such prepare to free the trace buffer.
 672                  */
 673                 buf = drvdata->buf;
 674                 drvdata->buf = NULL;
 675         }
 676
 677         drvdata->reading = false;
 678         spin_unlock_irqrestore(&drvdata->spinlock, flags);
 679
 680         /*
 681          * Free allocated memory outside of the spinlock.  There is no need
 682          * to assert the validity of 'buf' since calling kfree(NULL) is safe.
 683          */
 684         kfree(buf);
 685
 686         return 0;
 687 }