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 /* Run a single AUX_CH I2C transaction, writing/reading data as necessary */
  43 static int
  44 i2c_algo_dp_aux_transaction(struct i2c_adapter *adapter, int mode,
  45                             uint8_t write_byte, uint8_t *read_byte)
  46 {
  47         struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
  48         int ret;
  49
  50         ret = (*algo_data->aux_ch)(adapter, mode,
  51                                    write_byte, read_byte);
  52         return ret;
  53 }
  54
  55 /*
  56  * I2C over AUX CH
  57  */
  58
  59 /*
  60  * Send the address. If the I2C link is running, this 'restarts'
  61  * the connection with the new address, this is used for doing
  62  * a write followed by a read (as needed for DDC)
  63  */
  64 static int
  65 i2c_algo_dp_aux_address(struct i2c_adapter *adapter, u16 address, bool reading)
  66 {
  67         struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
  68         int mode = MODE_I2C_START;
  69         int ret;
  70
  71         if (reading)
  72                 mode |= MODE_I2C_READ;
  73         else
  74                 mode |= MODE_I2C_WRITE;
  75         algo_data->address = address;
  76         algo_data->running = true;
  77         ret = i2c_algo_dp_aux_transaction(adapter, mode, 0, NULL);
  78         return ret;
  79 }
  80
  81 /*
  82  * Stop the I2C transaction. This closes out the link, sending
  83  * a bare address packet with the MOT bit turned off
  84  */
  85 static void
  86 i2c_algo_dp_aux_stop(struct i2c_adapter *adapter, bool reading)
  87 {
  88         struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
  89         int mode = MODE_I2C_STOP;
  90
  91         if (reading)
  92                 mode |= MODE_I2C_READ;
  93         else
  94                 mode |= MODE_I2C_WRITE;
  95         if (algo_data->running) {
  96                 (void) i2c_algo_dp_aux_transaction(adapter, mode, 0, NULL);
  97                 algo_data->running = false;
  98         }
  99 }
 100
 101 /*
 102  * Write a single byte to the current I2C address, the
 103  * the I2C link must be running or this returns -EIO
 104  */
 105 static int
 106 i2c_algo_dp_aux_put_byte(struct i2c_adapter *adapter, u8 byte)
 107 {
 108         struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
 109         int ret;
 110
 111         if (!algo_data->running)
 112                 return -EIO;
 113
 114         ret = i2c_algo_dp_aux_transaction(adapter, MODE_I2C_WRITE, byte, NULL);
 115         return ret;
 116 }
 117
 118 /*
 119  * Read a single byte from the current I2C address, the
 120  * I2C link must be running or this returns -EIO
 121  */
 122 static int
 123 i2c_algo_dp_aux_get_byte(struct i2c_adapter *adapter, u8 *byte_ret)
 124 {
 125         struct i2c_algo_dp_aux_data *algo_data = adapter->algo_data;
 126         int ret;
 127
 128         if (!algo_data->running)
 129                 return -EIO;
 130
 131         ret = i2c_algo_dp_aux_transaction(adapter, MODE_I2C_READ, 0, byte_ret);
 132         return ret;
 133 }
 134
 135 static int
 136 i2c_algo_dp_aux_xfer(struct i2c_adapter *adapter,
 137                      struct i2c_msg *msgs,
 138                      int num)
 139 {
 140         int ret = 0;
 141         bool reading = false;
 142         int m;
 143         int b;
 144
 145         for (m = 0; m < num; m++) {
 146                 u16 len = msgs[m].len;
 147                 u8 *buf = msgs[m].buf;
 148                 reading = (msgs[m].flags & I2C_M_RD) != 0;
 149                 ret = i2c_algo_dp_aux_address(adapter, msgs[m].addr, reading);
 150                 if (ret < 0)
 151                         break;
 152                 if (reading) {
 153                         for (b = 0; b < len; b++) {
 154                                 ret = i2c_algo_dp_aux_get_byte(adapter, &buf[b]);
 155                                 if (ret < 0)
 156                                         break;
 157                         }
 158                 } else {
 159                         for (b = 0; b < len; b++) {
 160                                 ret = i2c_algo_dp_aux_put_byte(adapter, buf[b]);
 161                                 if (ret < 0)
 162                                         break;
 163                         }
 164                 }
 165                 if (ret < 0)
 166                         break;
 167         }
 168         if (ret >= 0)
 169                 ret = num;
 170         i2c_algo_dp_aux_stop(adapter, reading);
 171         DRM_DEBUG_KMS("dp_aux_xfer return %d\n", ret);
 172         return ret;
 173 }
 174
 175 static u32
 176 i2c_algo_dp_aux_functionality(struct i2c_adapter *adapter)
 177 {
 178         return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
 179                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 180                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 181                I2C_FUNC_10BIT_ADDR;
 182 }
 183
 184 static const struct i2c_algorithm i2c_dp_aux_algo = {
 185         .master_xfer    = i2c_algo_dp_aux_xfer,
 186         .functionality  = i2c_algo_dp_aux_functionality,
 187 };
 188
 189 static void
 190 i2c_dp_aux_reset_bus(struct i2c_adapter *adapter)
 191 {
 192         (void) i2c_algo_dp_aux_address(adapter, 0, false);
 193         (void) i2c_algo_dp_aux_stop(adapter, false);
 194 }
 195
 196 static int
 197 i2c_dp_aux_prepare_bus(struct i2c_adapter *adapter)
 198 {
 199         adapter->algo = &i2c_dp_aux_algo;
 200         adapter->retries = 3;
 201         i2c_dp_aux_reset_bus(adapter);
 202         return 0;
 203 }
 204
 205 /**
 206  * i2c_dp_aux_add_bus() - register an i2c adapter using the aux ch helper
 207  * @adapter: i2c adapter to register
 208  *
 209  * This registers an i2c adapater that uses dp aux channel as it's underlaying
 210  * transport. The driver needs to fill out the &i2c_algo_dp_aux_data structure
 211  * and store it in the algo_data member of the @adapter argument. This will be
 212  * used by the i2c over dp aux algorithm to drive the hardware.
 213  *
 214  * RETURNS:
 215  * 0 on success, -ERRNO on failure.
 216  */
 217 int
 218 i2c_dp_aux_add_bus(struct i2c_adapter *adapter)
 219 {
 220         int error;
 221
 222         error = i2c_dp_aux_prepare_bus(adapter);
 223         if (error)
 224                 return error;
 225         error = i2c_add_adapter(adapter);
 226         return error;
 227 }
 228 EXPORT_SYMBOL(i2c_dp_aux_add_bus);
 229
 230 /* Helpers for DP link training */
 231 static u8 dp_link_status(const u8 link_status[DP_LINK_STATUS_SIZE], int r)
 232 {
 233         return link_status[r - DP_LANE0_1_STATUS];
 234 }
 235
 236 static u8 dp_get_lane_status(const u8 link_status[DP_LINK_STATUS_SIZE],
 237                              int lane)
 238 {
 239         int i = DP_LANE0_1_STATUS + (lane >> 1);
 240         int s = (lane & 1) * 4;
 241         u8 l = dp_link_status(link_status, i);
 242         return (l >> s) & 0xf;
 243 }
 244
 245 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
 246                           int lane_count)
 247 {
 248         u8 lane_align;
 249         u8 lane_status;
 250         int lane;
 251
 252         lane_align = dp_link_status(link_status,
 253                                     DP_LANE_ALIGN_STATUS_UPDATED);
 254         if ((lane_align & DP_INTERLANE_ALIGN_DONE) == 0)
 255                 return false;
 256         for (lane = 0; lane < lane_count; lane++) {
 257                 lane_status = dp_get_lane_status(link_status, lane);
 258                 if ((lane_status & DP_CHANNEL_EQ_BITS) != DP_CHANNEL_EQ_BITS)
 259                         return false;
 260         }
 261         return true;
 262 }
 263 EXPORT_SYMBOL(drm_dp_channel_eq_ok);
 264
 265 bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
 266                               int lane_count)
 267 {
 268         int lane;
 269         u8 lane_status;
 270
 271         for (lane = 0; lane < lane_count; lane++) {
 272                 lane_status = dp_get_lane_status(link_status, lane);
 273                 if ((lane_status & DP_LANE_CR_DONE) == 0)
 274                         return false;
 275         }
 276         return true;
 277 }
 278 EXPORT_SYMBOL(drm_dp_clock_recovery_ok);
 279
 280 u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE],
 281                                      int lane)
 282 {
 283         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
 284         int s = ((lane & 1) ?
 285                  DP_ADJUST_VOLTAGE_SWING_LANE1_SHIFT :
 286                  DP_ADJUST_VOLTAGE_SWING_LANE0_SHIFT);
 287         u8 l = dp_link_status(link_status, i);
 288
 289         return ((l >> s) & 0x3) << DP_TRAIN_VOLTAGE_SWING_SHIFT;
 290 }
 291 EXPORT_SYMBOL(drm_dp_get_adjust_request_voltage);
 292
 293 u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],
 294                                           int lane)
 295 {
 296         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
 297         int s = ((lane & 1) ?
 298                  DP_ADJUST_PRE_EMPHASIS_LANE1_SHIFT :
 299                  DP_ADJUST_PRE_EMPHASIS_LANE0_SHIFT);
 300         u8 l = dp_link_status(link_status, i);
 301
 302         return ((l >> s) & 0x3) << DP_TRAIN_PRE_EMPHASIS_SHIFT;
 303 }
 304 EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
 305
 306 void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 307         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 308                 udelay(100);
 309         else
 310                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 311 }
 312 EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
 313
 314 void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 315         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 316                 udelay(400);
 317         else
 318                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 319 }
 320 EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
 321
 322 u8 drm_dp_link_rate_to_bw_code(int link_rate)
 323 {
 324         switch (link_rate) {
 325         case 162000:
 326         default:
 327                 return DP_LINK_BW_1_62;
 328         case 270000:
 329                 return DP_LINK_BW_2_7;
 330         case 540000:
 331                 return DP_LINK_BW_5_4;
 332         }
 333 }
 334 EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code);
 335
 336 int drm_dp_bw_code_to_link_rate(u8 link_bw)
 337 {
 338         switch (link_bw) {
 339         case DP_LINK_BW_1_62:
 340         default:
 341                 return 162000;
 342         case DP_LINK_BW_2_7:
 343                 return 270000;
 344         case DP_LINK_BW_5_4:
 345                 return 540000;
 346         }
 347 }
 348 EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
 349
 350 /**
 351  * DOC: dp helpers
 352  *
 353  * The DisplayPort AUX channel is an abstraction to allow generic, driver-
 354  * independent access to AUX functionality. Drivers can take advantage of
 355  * this by filling in the fields of the drm_dp_aux structure.
 356  *
 357  * Transactions are described using a hardware-independent drm_dp_aux_msg
 358  * structure, which is passed into a driver's .transfer() implementation.
 359  * Both native and I2C-over-AUX transactions are supported.
 360  */
 361
 362 static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 363                               unsigned int offset, void *buffer, size_t size)
 364 {
 365         struct drm_dp_aux_msg msg;
 366         unsigned int retry;
 367         int err;
 368
 369         memset(&msg, 0, sizeof(msg));
 370         msg.address = offset;
 371         msg.request = request;
 372         msg.buffer = buffer;
 373         msg.size = size;
 374
 375         /*
 376          * The specification doesn't give any recommendation on how often to
 377          * retry native transactions, so retry 7 times like for I2C-over-AUX
 378          * transactions.
 379          */
 380         for (retry = 0; retry < 7; retry++) {
 381                 err = aux->transfer(aux, &msg);
 382                 if (err < 0) {
 383                         if (err == -EBUSY)
 384                                 continue;
 385
 386                         return err;
 387                 }
 388
 389                 if (err < size)
 390                         return -EPROTO;
 391
 392                 switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
 393                 case DP_AUX_NATIVE_REPLY_ACK:
 394                         return err;
 395
 396                 case DP_AUX_NATIVE_REPLY_NACK:
 397                         return -EIO;
 398
 399                 case DP_AUX_NATIVE_REPLY_DEFER:
 400                         usleep_range(400, 500);
 401                         break;
 402                 }
 403         }
 404
 405         DRM_ERROR("too many retries, giving up\n");
 406         return -EIO;
 407 }
 408
 409 /**
 410  * drm_dp_dpcd_read() - read a series of bytes from the DPCD
 411  * @aux: DisplayPort AUX channel
 412  * @offset: address of the (first) register to read
 413  * @buffer: buffer to store the register values
 414  * @size: number of bytes in @buffer
 415  *
 416  * Returns the number of bytes transferred on success, or a negative error
 417  * code on failure. -EIO is returned if the request was NAKed by the sink or
 418  * if the retry count was exceeded. If not all bytes were transferred, this
 419  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 420  * function, with the exception of -EBUSY (which causes the transaction to
 421  * be retried), are propagated to the caller.
 422  */
 423 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
 424                          void *buffer, size_t size)
 425 {
 426         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer,
 427                                   size);
 428 }
 429 EXPORT_SYMBOL(drm_dp_dpcd_read);
 430
 431 /**
 432  * drm_dp_dpcd_write() - write a series of bytes to the DPCD
 433  * @aux: DisplayPort AUX channel
 434  * @offset: address of the (first) register to write
 435  * @buffer: buffer containing the values to write
 436  * @size: number of bytes in @buffer
 437  *
 438  * Returns the number of bytes transferred on success, or a negative error
 439  * code on failure. -EIO is returned if the request was NAKed by the sink or
 440  * if the retry count was exceeded. If not all bytes were transferred, this
 441  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 442  * function, with the exception of -EBUSY (which causes the transaction to
 443  * be retried), are propagated to the caller.
 444  */
 445 ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
 446                           void *buffer, size_t size)
 447 {
 448         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer,
 449                                   size);
 450 }
 451 EXPORT_SYMBOL(drm_dp_dpcd_write);
 452
 453 /**
 454  * drm_dp_dpcd_read_link_status() - read DPCD link status (bytes 0x202-0x207)
 455  * @aux: DisplayPort AUX channel
 456  * @status: buffer to store the link status in (must be at least 6 bytes)
 457  *
 458  * Returns the number of bytes transferred on success or a negative error
 459  * code on failure.
 460  */
 461 int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 462                                  u8 status[DP_LINK_STATUS_SIZE])
 463 {
 464         return drm_dp_dpcd_read(aux, DP_LANE0_1_STATUS, status,
 465                                 DP_LINK_STATUS_SIZE);
 466 }
 467 EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
 468
 469 /**
 470  * drm_dp_link_probe() - probe a DisplayPort link for capabilities
 471  * @aux: DisplayPort AUX channel
 472  * @link: pointer to structure in which to return link capabilities
 473  *
 474  * The structure filled in by this function can usually be passed directly
 475  * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and
 476  * configure the link based on the link's capabilities.
 477  *
 478  * Returns 0 on success or a negative error code on failure.
 479  */
 480 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 481 {
 482         u8 values[3];
 483         int err;
 484
 485         memset(link, 0, sizeof(*link));
 486
 487         err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));
 488         if (err < 0)
 489                 return err;
 490
 491         link->revision = values[0];
 492         link->rate = drm_dp_bw_code_to_link_rate(values[1]);
 493         link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK;
 494
 495         if (values[2] & DP_ENHANCED_FRAME_CAP)
 496                 link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;
 497
 498         return 0;
 499 }
 500 EXPORT_SYMBOL(drm_dp_link_probe);
 501
 502 /**
 503  * drm_dp_link_power_up() - power up a DisplayPort link
 504  * @aux: DisplayPort AUX channel
 505  * @link: pointer to a structure containing the link configuration
 506  *
 507  * Returns 0 on success or a negative error code on failure.
 508  */
 509 int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
 510 {
 511         u8 value;
 512         int err;
 513
 514         /* DP_SET_POWER register is only available on DPCD v1.1 and later */
 515         if (link->revision < 0x11)
 516                 return 0;
 517
 518         err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
 519         if (err < 0)
 520                 return err;
 521
 522         value &= ~DP_SET_POWER_MASK;
 523         value |= DP_SET_POWER_D0;
 524
 525         err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
 526         if (err < 0)
 527                 return err;
 528
 529         /*
 530          * According to the DP 1.1 specification, a "Sink Device must exit the
 531          * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
 532          * Control Field" (register 0x600).
 533          */
 534         usleep_range(1000, 2000);
 535
 536         return 0;
 537 }
 538 EXPORT_SYMBOL(drm_dp_link_power_up);
 539
 540 /**
 541  * drm_dp_link_configure() - configure a DisplayPort link
 542  * @aux: DisplayPort AUX channel
 543  * @link: pointer to a structure containing the link configuration
 544  *
 545  * Returns 0 on success or a negative error code on failure.
 546  */
 547 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 548 {
 549         u8 values[2];
 550         int err;
 551
 552         values[0] = drm_dp_link_rate_to_bw_code(link->rate);
 553         values[1] = link->num_lanes;
 554
 555         if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)
 556                 values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
 557
 558         err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));
 559         if (err < 0)
 560                 return err;
 561
 562         return 0;
 563 }
 564 EXPORT_SYMBOL(drm_dp_link_configure);
 565
 566 /*
 567  * I2C-over-AUX implementation
 568  */
 569
 570 static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
 571 {
 572         return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
 573                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 574                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 575                I2C_FUNC_10BIT_ADDR;
 576 }
 577
 578 /*
 579  * Transfer a single I2C-over-AUX message and handle various error conditions,
 580  * retrying the transaction as appropriate.
 581  */
 582 static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 583 {
 584         unsigned int retry;
 585         int err;
 586
 587         /*
 588          * DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
 589          * is required to retry at least seven times upon receiving AUX_DEFER
 590          * before giving up the AUX transaction.
 591          */
 592         for (retry = 0; retry < 7; retry++) {
 593                 err = aux->transfer(aux, msg);
 594                 if (err < 0) {
 595                         if (err == -EBUSY)
 596                                 continue;
 597
 598                         DRM_DEBUG_KMS("transaction failed: %d\n", err);
 599                         return err;
 600                 }
 601
 602                 if (err < msg->size)
 603                         return -EPROTO;
 604
 605                 switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
 606                 case DP_AUX_NATIVE_REPLY_ACK:
 607                         /*
 608                          * For I2C-over-AUX transactions this isn't enough, we
 609                          * need to check for the I2C ACK reply.
 610                          */
 611                         break;
 612
 613                 case DP_AUX_NATIVE_REPLY_NACK:
 614                         DRM_DEBUG_KMS("native nack\n");
 615                         return -EREMOTEIO;
 616
 617                 case DP_AUX_NATIVE_REPLY_DEFER:
 618                         DRM_DEBUG_KMS("native defer");
 619                         /*
 620                          * We could check for I2C bit rate capabilities and if
 621                          * available adjust this interval. We could also be
 622                          * more careful with DP-to-legacy adapters where a
 623                          * long legacy cable may force very low I2C bit rates.
 624                          *
 625                          * For now just defer for long enough to hopefully be
 626                          * safe for all use-cases.
 627                          */
 628                         usleep_range(500, 600);
 629                         continue;
 630
 631                 default:
 632                         DRM_ERROR("invalid native reply %#04x\n", msg->reply);
 633                         return -EREMOTEIO;
 634                 }
 635
 636                 switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
 637                 case DP_AUX_I2C_REPLY_ACK:
 638                         /*
 639                          * Both native ACK and I2C ACK replies received. We
 640                          * can assume the transfer was successful.
 641                          */
 642                         return 0;
 643
 644                 case DP_AUX_I2C_REPLY_NACK:
 645                         DRM_DEBUG_KMS("I2C nack\n");
 646                         return -EREMOTEIO;
 647
 648                 case DP_AUX_I2C_REPLY_DEFER:
 649                         DRM_DEBUG_KMS("I2C defer\n");
 650                         usleep_range(400, 500);
 651                         continue;
 652
 653                 default:
 654                         DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
 655                         return -EREMOTEIO;
 656                 }
 657         }
 658
 659         DRM_ERROR("too many retries, giving up\n");
 660         return -EREMOTEIO;
 661 }
 662
 663 static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 664                            int num)
 665 {
 666         struct drm_dp_aux *aux = adapter->algo_data;
 667         unsigned int i, j;
 668
 669         for (i = 0; i < num; i++) {
 670                 struct drm_dp_aux_msg msg;
 671                 int err;
 672
 673                 /*
 674                  * Many hardware implementations support FIFOs larger than a
 675                  * single byte, but it has been empirically determined that
 676                  * transferring data in larger chunks can actually lead to
 677                  * decreased performance. Therefore each message is simply
 678                  * transferred byte-by-byte.
 679                  */
 680                 for (j = 0; j < msgs[i].len; j++) {
 681                         memset(&msg, 0, sizeof(msg));
 682                         msg.address = msgs[i].addr;
 683
 684                         msg.request = (msgs[i].flags & I2C_M_RD) ?
 685                                         DP_AUX_I2C_READ :
 686                                         DP_AUX_I2C_WRITE;
 687
 688                         /*
 689                          * All messages except the last one are middle-of-
 690                          * transfer messages.
 691                          */
 692                         if ((i < num - 1) || (j < msgs[i].len - 1))
 693                                 msg.request |= DP_AUX_I2C_MOT;
 694
 695                         msg.buffer = msgs[i].buf + j;
 696                         msg.size = 1;
 697
 698                         err = drm_dp_i2c_do_msg(aux, &msg);
 699                         if (err < 0)
 700                                 return err;
 701                 }
 702         }
 703
 704         return num;
 705 }
 706
 707 static const struct i2c_algorithm drm_dp_i2c_algo = {
 708         .functionality = drm_dp_i2c_functionality,
 709         .master_xfer = drm_dp_i2c_xfer,
 710 };
 711
 712 /**
 713  * drm_dp_aux_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
 714  * @aux: DisplayPort AUX channel
 715  *
 716  * Returns 0 on success or a negative error code on failure.
 717  */
 718 int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux)
 719 {
 720         aux->ddc.algo = &drm_dp_i2c_algo;
 721         aux->ddc.algo_data = aux;
 722         aux->ddc.retries = 3;
 723
 724         aux->ddc.class = I2C_CLASS_DDC;
 725         aux->ddc.owner = THIS_MODULE;
 726         aux->ddc.dev.parent = aux->dev;
 727         aux->ddc.dev.of_node = aux->dev->of_node;
 728
 729         strncpy(aux->ddc.name, dev_name(aux->dev), sizeof(aux->ddc.name));
 730
 731         return i2c_add_adapter(&aux->ddc);
 732 }
 733 EXPORT_SYMBOL(drm_dp_aux_register_i2c_bus);
 734
 735 /**
 736  * drm_dp_aux_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
 737  * @aux: DisplayPort AUX channel
 738  */
 739 void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux)
 740 {
 741         i2c_del_adapter(&aux->ddc);
 742 }
 743 EXPORT_SYMBOL(drm_dp_aux_unregister_i2c_bus);