drivers/gpu/drm/drm_dp_helper.c

   1 /*
   2  * Copyright © 2009 Keith Packard
   3  *
   4  * Permission to use, copy, modify, distribute, and sell this software and its
   5  * documentation for any purpose is hereby granted without fee, provided that
   6  * the above copyright notice appear in all copies and that both that copyright
   7  * notice and this permission notice appear in supporting documentation, and
   8  * that the name of the copyright holders not be used in advertising or
   9  * publicity pertaining to distribution of the software without specific,
  10  * written prior permission.  The copyright holders make no representations
  11  * about the suitability of this software for any purpose.  It is provided "as
  12  * is" without express or implied warranty.
  13  *
  14  * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  15  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
  16  * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
  17  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
  18  * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
  19  * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
  20  * OF THIS SOFTWARE.
  21  */
  22
  23 #include <linux/kernel.h>
  24 #include <linux/module.h>
  25 #include <linux/delay.h>
  26 #include <linux/init.h>
  27 #include <linux/errno.h>
  28 #include <linux/sched.h>
  29 #include <linux/i2c.h>
  30 #include <drm/drm_dp_helper.h>
  31 #include <drm/drmP.h>
  32
  33 /**
  34  * DOC: dp helpers
  35  *
  36  * These functions contain some common logic and helpers at various abstraction
  37  * levels to deal with Display Port sink devices and related things like DP aux
  38  * channel transfers, EDID reading over DP aux channels, decoding certain DPCD
  39  * blocks, ...
  40  */
  41
  42 /* Helpers for DP link training */
  43 static u8 dp_link_status(const u8 link_status[DP_LINK_STATUS_SIZE], int r)
  44 {
  45         return link_status[r - DP_LANE0_1_STATUS];
  46 }
  47
  48 static u8 dp_get_lane_status(const u8 link_status[DP_LINK_STATUS_SIZE],
  49                              int lane)
  50 {
  51         int i = DP_LANE0_1_STATUS + (lane >> 1);
  52         int s = (lane & 1) * 4;
  53         u8 l = dp_link_status(link_status, i);
  54         return (l >> s) & 0xf;
  55 }
  56
  57 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
  58                           int lane_count)
  59 {
  60         u8 lane_align;
  61         u8 lane_status;
  62         int lane;
  63
  64         lane_align = dp_link_status(link_status,
  65                                     DP_LANE_ALIGN_STATUS_UPDATED);
  66         if ((lane_align & DP_INTERLANE_ALIGN_DONE) == 0)
  67                 return false;
  68         for (lane = 0; lane < lane_count; lane++) {
  69                 lane_status = dp_get_lane_status(link_status, lane);
  70                 if ((lane_status & DP_CHANNEL_EQ_BITS) != DP_CHANNEL_EQ_BITS)
  71                         return false;
  72         }
  73         return true;
  74 }
  75 EXPORT_SYMBOL(drm_dp_channel_eq_ok);
  76
  77 bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
  78                               int lane_count)
  79 {
  80         int lane;
  81         u8 lane_status;
  82
  83         for (lane = 0; lane < lane_count; lane++) {
  84                 lane_status = dp_get_lane_status(link_status, lane);
  85                 if ((lane_status & DP_LANE_CR_DONE) == 0)
  86                         return false;
  87         }
  88         return true;
  89 }
  90 EXPORT_SYMBOL(drm_dp_clock_recovery_ok);
  91
  92 u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE],
  93                                      int lane)
  94 {
  95         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
  96         int s = ((lane & 1) ?
  97                  DP_ADJUST_VOLTAGE_SWING_LANE1_SHIFT :
  98                  DP_ADJUST_VOLTAGE_SWING_LANE0_SHIFT);
  99         u8 l = dp_link_status(link_status, i);
 100
 101         return ((l >> s) & 0x3) << DP_TRAIN_VOLTAGE_SWING_SHIFT;
 102 }
 103 EXPORT_SYMBOL(drm_dp_get_adjust_request_voltage);
 104
 105 u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],
 106                                           int lane)
 107 {
 108         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
 109         int s = ((lane & 1) ?
 110                  DP_ADJUST_PRE_EMPHASIS_LANE1_SHIFT :
 111                  DP_ADJUST_PRE_EMPHASIS_LANE0_SHIFT);
 112         u8 l = dp_link_status(link_status, i);
 113
 114         return ((l >> s) & 0x3) << DP_TRAIN_PRE_EMPHASIS_SHIFT;
 115 }
 116 EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
 117
 118 void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 119         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 120                 udelay(100);
 121         else
 122                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 123 }
 124 EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
 125
 126 void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 127         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 128                 udelay(400);
 129         else
 130                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 131 }
 132 EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
 133
 134 u8 drm_dp_link_rate_to_bw_code(int link_rate)
 135 {
 136         switch (link_rate) {
 137         case 162000:
 138         default:
 139                 return DP_LINK_BW_1_62;
 140         case 270000:
 141                 return DP_LINK_BW_2_7;
 142         case 540000:
 143                 return DP_LINK_BW_5_4;
 144         }
 145 }
 146 EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code);
 147
 148 int drm_dp_bw_code_to_link_rate(u8 link_bw)
 149 {
 150         switch (link_bw) {
 151         case DP_LINK_BW_1_62:
 152         default:
 153                 return 162000;
 154         case DP_LINK_BW_2_7:
 155                 return 270000;
 156         case DP_LINK_BW_5_4:
 157                 return 540000;
 158         }
 159 }
 160 EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
 161
 162 /**
 163  * DOC: dp helpers
 164  *
 165  * The DisplayPort AUX channel is an abstraction to allow generic, driver-
 166  * independent access to AUX functionality. Drivers can take advantage of
 167  * this by filling in the fields of the drm_dp_aux structure.
 168  *
 169  * Transactions are described using a hardware-independent drm_dp_aux_msg
 170  * structure, which is passed into a driver's .transfer() implementation.
 171  * Both native and I2C-over-AUX transactions are supported.
 172  */
 173
 174 static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 175                               unsigned int offset, void *buffer, size_t size)
 176 {
 177         struct drm_dp_aux_msg msg;
 178         unsigned int retry;
 179         int err;
 180
 181         memset(&msg, 0, sizeof(msg));
 182         msg.address = offset;
 183         msg.request = request;
 184         msg.buffer = buffer;
 185         msg.size = size;
 186
 187         /*
 188          * The specification doesn't give any recommendation on how often to
 189          * retry native transactions. We used to retry 7 times like for
 190          * aux i2c transactions but real world devices this wasn't
 191          * sufficient, bump to 32 which makes Dell 4k monitors happier.
 192          */
 193         for (retry = 0; retry < 32; retry++) {
 194
 195                 mutex_lock(&aux->hw_mutex);
 196                 err = aux->transfer(aux, &msg);
 197                 mutex_unlock(&aux->hw_mutex);
 198                 if (err < 0) {
 199                         if (err == -EBUSY)
 200                                 continue;
 201
 202                         return err;
 203                 }
 204
 205
 206                 switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
 207                 case DP_AUX_NATIVE_REPLY_ACK:
 208                         if (err < size)
 209                                 return -EPROTO;
 210                         return err;
 211
 212                 case DP_AUX_NATIVE_REPLY_NACK:
 213                         return -EIO;
 214
 215                 case DP_AUX_NATIVE_REPLY_DEFER:
 216                         usleep_range(400, 500);
 217                         break;
 218                 }
 219         }
 220
 221         DRM_DEBUG_KMS("too many retries, giving up\n");
 222         return -EIO;
 223 }
 224
 225 /**
 226  * drm_dp_dpcd_read() - read a series of bytes from the DPCD
 227  * @aux: DisplayPort AUX channel
 228  * @offset: address of the (first) register to read
 229  * @buffer: buffer to store the register values
 230  * @size: number of bytes in @buffer
 231  *
 232  * Returns the number of bytes transferred on success, or a negative error
 233  * code on failure. -EIO is returned if the request was NAKed by the sink or
 234  * if the retry count was exceeded. If not all bytes were transferred, this
 235  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 236  * function, with the exception of -EBUSY (which causes the transaction to
 237  * be retried), are propagated to the caller.
 238  */
 239 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
 240                          void *buffer, size_t size)
 241 {
 242         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer,
 243                                   size);
 244 }
 245 EXPORT_SYMBOL(drm_dp_dpcd_read);
 246
 247 /**
 248  * drm_dp_dpcd_write() - write a series of bytes to the DPCD
 249  * @aux: DisplayPort AUX channel
 250  * @offset: address of the (first) register to write
 251  * @buffer: buffer containing the values to write
 252  * @size: number of bytes in @buffer
 253  *
 254  * Returns the number of bytes transferred on success, or a negative error
 255  * code on failure. -EIO is returned if the request was NAKed by the sink or
 256  * if the retry count was exceeded. If not all bytes were transferred, this
 257  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 258  * function, with the exception of -EBUSY (which causes the transaction to
 259  * be retried), are propagated to the caller.
 260  */
 261 ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
 262                           void *buffer, size_t size)
 263 {
 264         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer,
 265                                   size);
 266 }
 267 EXPORT_SYMBOL(drm_dp_dpcd_write);
 268
 269 /**
 270  * drm_dp_dpcd_read_link_status() - read DPCD link status (bytes 0x202-0x207)
 271  * @aux: DisplayPort AUX channel
 272  * @status: buffer to store the link status in (must be at least 6 bytes)
 273  *
 274  * Returns the number of bytes transferred on success or a negative error
 275  * code on failure.
 276  */
 277 int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 278                                  u8 status[DP_LINK_STATUS_SIZE])
 279 {
 280         return drm_dp_dpcd_read(aux, DP_LANE0_1_STATUS, status,
 281                                 DP_LINK_STATUS_SIZE);
 282 }
 283 EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
 284
 285 /**
 286  * drm_dp_link_probe() - probe a DisplayPort link for capabilities
 287  * @aux: DisplayPort AUX channel
 288  * @link: pointer to structure in which to return link capabilities
 289  *
 290  * The structure filled in by this function can usually be passed directly
 291  * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and
 292  * configure the link based on the link's capabilities.
 293  *
 294  * Returns 0 on success or a negative error code on failure.
 295  */
 296 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 297 {
 298         u8 values[3];
 299         int err;
 300
 301         memset(link, 0, sizeof(*link));
 302
 303         err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));
 304         if (err < 0)
 305                 return err;
 306
 307         link->revision = values[0];
 308         link->rate = drm_dp_bw_code_to_link_rate(values[1]);
 309         link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK;
 310
 311         if (values[2] & DP_ENHANCED_FRAME_CAP)
 312                 link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;
 313
 314         return 0;
 315 }
 316 EXPORT_SYMBOL(drm_dp_link_probe);
 317
 318 /**
 319  * drm_dp_link_power_up() - power up a DisplayPort link
 320  * @aux: DisplayPort AUX channel
 321  * @link: pointer to a structure containing the link configuration
 322  *
 323  * Returns 0 on success or a negative error code on failure.
 324  */
 325 int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
 326 {
 327         u8 value;
 328         int err;
 329
 330         /* DP_SET_POWER register is only available on DPCD v1.1 and later */
 331         if (link->revision < 0x11)
 332                 return 0;
 333
 334         err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
 335         if (err < 0)
 336                 return err;
 337
 338         value &= ~DP_SET_POWER_MASK;
 339         value |= DP_SET_POWER_D0;
 340
 341         err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
 342         if (err < 0)
 343                 return err;
 344
 345         /*
 346          * According to the DP 1.1 specification, a "Sink Device must exit the
 347          * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
 348          * Control Field" (register 0x600).
 349          */
 350         usleep_range(1000, 2000);
 351
 352         return 0;
 353 }
 354 EXPORT_SYMBOL(drm_dp_link_power_up);
 355
 356 /**
 357  * drm_dp_link_power_down() - power down a DisplayPort link
 358  * @aux: DisplayPort AUX channel
 359  * @link: pointer to a structure containing the link configuration
 360  *
 361  * Returns 0 on success or a negative error code on failure.
 362  */
 363 int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link)
 364 {
 365         u8 value;
 366         int err;
 367
 368         /* DP_SET_POWER register is only available on DPCD v1.1 and later */
 369         if (link->revision < 0x11)
 370                 return 0;
 371
 372         err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
 373         if (err < 0)
 374                 return err;
 375
 376         value &= ~DP_SET_POWER_MASK;
 377         value |= DP_SET_POWER_D3;
 378
 379         err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
 380         if (err < 0)
 381                 return err;
 382
 383         return 0;
 384 }
 385 EXPORT_SYMBOL(drm_dp_link_power_down);
 386
 387 /**
 388  * drm_dp_link_configure() - configure a DisplayPort link
 389  * @aux: DisplayPort AUX channel
 390  * @link: pointer to a structure containing the link configuration
 391  *
 392  * Returns 0 on success or a negative error code on failure.
 393  */
 394 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 395 {
 396         u8 values[2];
 397         int err;
 398
 399         values[0] = drm_dp_link_rate_to_bw_code(link->rate);
 400         values[1] = link->num_lanes;
 401
 402         if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)
 403                 values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
 404
 405         err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));
 406         if (err < 0)
 407                 return err;
 408
 409         return 0;
 410 }
 411 EXPORT_SYMBOL(drm_dp_link_configure);
 412
 413 /*
 414  * I2C-over-AUX implementation
 415  */
 416
 417 static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
 418 {
 419         return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
 420                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 421                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 422                I2C_FUNC_10BIT_ADDR;
 423 }
 424
 425 /*
 426  * Transfer a single I2C-over-AUX message and handle various error conditions,
 427  * retrying the transaction as appropriate.  It is assumed that the
 428  * aux->transfer function does not modify anything in the msg other than the
 429  * reply field.
 430  *
 431  * Returns bytes transferred on success, or a negative error code on failure.
 432  */
 433 static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 434 {
 435         unsigned int retry;
 436         int ret;
 437
 438         /*
 439          * DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
 440          * is required to retry at least seven times upon receiving AUX_DEFER
 441          * before giving up the AUX transaction.
 442          */
 443         for (retry = 0; retry < 7; retry++) {
 444                 mutex_lock(&aux->hw_mutex);
 445                 ret = aux->transfer(aux, msg);
 446                 mutex_unlock(&aux->hw_mutex);
 447                 if (ret < 0) {
 448                         if (ret == -EBUSY)
 449                                 continue;
 450
 451                         DRM_DEBUG_KMS("transaction failed: %d\n", ret);
 452                         return ret;
 453                 }
 454
 455
 456                 switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
 457                 case DP_AUX_NATIVE_REPLY_ACK:
 458                         /*
 459                          * For I2C-over-AUX transactions this isn't enough, we
 460                          * need to check for the I2C ACK reply.
 461                          */
 462                         break;
 463
 464                 case DP_AUX_NATIVE_REPLY_NACK:
 465                         DRM_DEBUG_KMS("native nack (result=%d, size=%zu)\n", ret, msg->size);
 466                         return -EREMOTEIO;
 467
 468                 case DP_AUX_NATIVE_REPLY_DEFER:
 469                         DRM_DEBUG_KMS("native defer");
 470                         /*
 471                          * We could check for I2C bit rate capabilities and if
 472                          * available adjust this interval. We could also be
 473                          * more careful with DP-to-legacy adapters where a
 474                          * long legacy cable may force very low I2C bit rates.
 475                          *
 476                          * For now just defer for long enough to hopefully be
 477                          * safe for all use-cases.
 478                          */
 479                         usleep_range(500, 600);
 480                         continue;
 481
 482                 default:
 483                         DRM_ERROR("invalid native reply %#04x\n", msg->reply);
 484                         return -EREMOTEIO;
 485                 }
 486
 487                 switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
 488                 case DP_AUX_I2C_REPLY_ACK:
 489                         /*
 490                          * Both native ACK and I2C ACK replies received. We
 491                          * can assume the transfer was successful.
 492                          */
 493                         return ret;
 494
 495                 case DP_AUX_I2C_REPLY_NACK:
 496                         DRM_DEBUG_KMS("I2C nack (result=%d, size=%zu\n", ret, msg->size);
 497                         aux->i2c_nack_count++;
 498                         return -EREMOTEIO;
 499
 500                 case DP_AUX_I2C_REPLY_DEFER:
 501                         DRM_DEBUG_KMS("I2C defer\n");
 502                         aux->i2c_defer_count++;
 503                         usleep_range(400, 500);
 504                         continue;
 505
 506                 default:
 507                         DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
 508                         return -EREMOTEIO;
 509                 }
 510         }
 511
 512         DRM_DEBUG_KMS("too many retries, giving up\n");
 513         return -EREMOTEIO;
 514 }
 515
 516 /*
 517  * Keep retrying drm_dp_i2c_do_msg until all data has been transferred.
 518  *
 519  * Returns an error code on failure, or a recommended transfer size on success.
 520  */
 521 static int drm_dp_i2c_drain_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *orig_msg)
 522 {
 523         int err, ret = orig_msg->size;
 524         struct drm_dp_aux_msg msg = *orig_msg;
 525
 526         while (msg.size > 0) {
 527                 err = drm_dp_i2c_do_msg(aux, &msg);
 528                 if (err <= 0)
 529                         return err == 0 ? -EPROTO : err;
 530
 531                 if (err < msg.size && err < ret) {
 532                         DRM_DEBUG_KMS("Partial I2C reply: requested %zu bytes got %d bytes\n",
 533                                       msg.size, err);
 534                         ret = err;
 535                 }
 536
 537                 msg.size -= err;
 538                 msg.buffer += err;
 539         }
 540
 541         return ret;
 542 }
 543
 544 /*
 545  * Bizlink designed DP->DVI-D Dual Link adapters require the I2C over AUX
 546  * packets to be as large as possible. If not, the I2C transactions never
 547  * succeed. Hence the default is maximum.
 548  */
 549 static int dp_aux_i2c_transfer_size __read_mostly = DP_AUX_MAX_PAYLOAD_BYTES;
 550 module_param_unsafe(dp_aux_i2c_transfer_size, int, 0644);
 551 MODULE_PARM_DESC(dp_aux_i2c_transfer_size,
 552                  "Number of bytes to transfer in a single I2C over DP AUX CH message, (1-16, default 16)");
 553
 554 static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 555                            int num)
 556 {
 557         struct drm_dp_aux *aux = adapter->algo_data;
 558         unsigned int i, j;
 559         unsigned transfer_size;
 560         struct drm_dp_aux_msg msg;
 561         int err = 0;
 562
 563         dp_aux_i2c_transfer_size = clamp(dp_aux_i2c_transfer_size, 1, DP_AUX_MAX_PAYLOAD_BYTES);
 564
 565         memset(&msg, 0, sizeof(msg));
 566
 567         for (i = 0; i < num; i++) {
 568                 msg.address = msgs[i].addr;
 569                 msg.request = (msgs[i].flags & I2C_M_RD) ?
 570                         DP_AUX_I2C_READ :
 571                         DP_AUX_I2C_WRITE;
 572                 msg.request |= DP_AUX_I2C_MOT;
 573                 /* Send a bare address packet to start the transaction.
 574                  * Zero sized messages specify an address only (bare
 575                  * address) transaction.
 576                  */
 577                 msg.buffer = NULL;
 578                 msg.size = 0;
 579                 err = drm_dp_i2c_do_msg(aux, &msg);
 580                 if (err < 0)
 581                         break;
 582                 /* We want each transaction to be as large as possible, but
 583                  * we'll go to smaller sizes if the hardware gives us a
 584                  * short reply.
 585                  */
 586                 transfer_size = dp_aux_i2c_transfer_size;
 587                 for (j = 0; j < msgs[i].len; j += msg.size) {
 588                         msg.buffer = msgs[i].buf + j;
 589                         msg.size = min(transfer_size, msgs[i].len - j);
 590
 591                         err = drm_dp_i2c_drain_msg(aux, &msg);
 592                         if (err < 0)
 593                                 break;
 594                         transfer_size = err;
 595                 }
 596                 if (err < 0)
 597                         break;
 598         }
 599         if (err >= 0)
 600                 err = num;
 601         /* Send a bare address packet to close out the transaction.
 602          * Zero sized messages specify an address only (bare
 603          * address) transaction.
 604          */
 605         msg.request &= ~DP_AUX_I2C_MOT;
 606         msg.buffer = NULL;
 607         msg.size = 0;
 608         (void)drm_dp_i2c_do_msg(aux, &msg);
 609
 610         return err;
 611 }
 612
 613 static const struct i2c_algorithm drm_dp_i2c_algo = {
 614         .functionality = drm_dp_i2c_functionality,
 615         .master_xfer = drm_dp_i2c_xfer,
 616 };
 617
 618 /**
 619  * drm_dp_aux_register() - initialise and register aux channel
 620  * @aux: DisplayPort AUX channel
 621  *
 622  * Returns 0 on success or a negative error code on failure.
 623  */
 624 int drm_dp_aux_register(struct drm_dp_aux *aux)
 625 {
 626         mutex_init(&aux->hw_mutex);
 627
 628         aux->ddc.algo = &drm_dp_i2c_algo;
 629         aux->ddc.algo_data = aux;
 630         aux->ddc.retries = 3;
 631
 632         aux->ddc.class = I2C_CLASS_DDC;
 633         aux->ddc.owner = THIS_MODULE;
 634         aux->ddc.dev.parent = aux->dev;
 635         aux->ddc.dev.of_node = aux->dev->of_node;
 636
 637         strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
 638                 sizeof(aux->ddc.name));
 639
 640         return i2c_add_adapter(&aux->ddc);
 641 }
 642 EXPORT_SYMBOL(drm_dp_aux_register);
 643
 644 /**
 645  * drm_dp_aux_unregister() - unregister an AUX adapter
 646  * @aux: DisplayPort AUX channel
 647  */
 648 void drm_dp_aux_unregister(struct drm_dp_aux *aux)
 649 {
 650         i2c_del_adapter(&aux->ddc);
 651 }
 652 EXPORT_SYMBOL(drm_dp_aux_unregister);