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 adapter 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  * IMPORTANT:
 218  * This interface is deprecated, please switch to the new dp aux helpers and
 219  * drm_dp_aux_register().
 220  */
 221 int
 222 i2c_dp_aux_add_bus(struct i2c_adapter *adapter)
 223 {
 224         int error;
 225
 226         error = i2c_dp_aux_prepare_bus(adapter);
 227         if (error)
 228                 return error;
 229         error = i2c_add_adapter(adapter);
 230         return error;
 231 }
 232 EXPORT_SYMBOL(i2c_dp_aux_add_bus);
 233
 234 /* Helpers for DP link training */
 235 static u8 dp_link_status(const u8 link_status[DP_LINK_STATUS_SIZE], int r)
 236 {
 237         return link_status[r - DP_LANE0_1_STATUS];
 238 }
 239
 240 static u8 dp_get_lane_status(const u8 link_status[DP_LINK_STATUS_SIZE],
 241                              int lane)
 242 {
 243         int i = DP_LANE0_1_STATUS + (lane >> 1);
 244         int s = (lane & 1) * 4;
 245         u8 l = dp_link_status(link_status, i);
 246         return (l >> s) & 0xf;
 247 }
 248
 249 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
 250                           int lane_count)
 251 {
 252         u8 lane_align;
 253         u8 lane_status;
 254         int lane;
 255
 256         lane_align = dp_link_status(link_status,
 257                                     DP_LANE_ALIGN_STATUS_UPDATED);
 258         if ((lane_align & DP_INTERLANE_ALIGN_DONE) == 0)
 259                 return false;
 260         for (lane = 0; lane < lane_count; lane++) {
 261                 lane_status = dp_get_lane_status(link_status, lane);
 262                 if ((lane_status & DP_CHANNEL_EQ_BITS) != DP_CHANNEL_EQ_BITS)
 263                         return false;
 264         }
 265         return true;
 266 }
 267 EXPORT_SYMBOL(drm_dp_channel_eq_ok);
 268
 269 bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
 270                               int lane_count)
 271 {
 272         int lane;
 273         u8 lane_status;
 274
 275         for (lane = 0; lane < lane_count; lane++) {
 276                 lane_status = dp_get_lane_status(link_status, lane);
 277                 if ((lane_status & DP_LANE_CR_DONE) == 0)
 278                         return false;
 279         }
 280         return true;
 281 }
 282 EXPORT_SYMBOL(drm_dp_clock_recovery_ok);
 283
 284 u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE],
 285                                      int lane)
 286 {
 287         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
 288         int s = ((lane & 1) ?
 289                  DP_ADJUST_VOLTAGE_SWING_LANE1_SHIFT :
 290                  DP_ADJUST_VOLTAGE_SWING_LANE0_SHIFT);
 291         u8 l = dp_link_status(link_status, i);
 292
 293         return ((l >> s) & 0x3) << DP_TRAIN_VOLTAGE_SWING_SHIFT;
 294 }
 295 EXPORT_SYMBOL(drm_dp_get_adjust_request_voltage);
 296
 297 u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],
 298                                           int lane)
 299 {
 300         int i = DP_ADJUST_REQUEST_LANE0_1 + (lane >> 1);
 301         int s = ((lane & 1) ?
 302                  DP_ADJUST_PRE_EMPHASIS_LANE1_SHIFT :
 303                  DP_ADJUST_PRE_EMPHASIS_LANE0_SHIFT);
 304         u8 l = dp_link_status(link_status, i);
 305
 306         return ((l >> s) & 0x3) << DP_TRAIN_PRE_EMPHASIS_SHIFT;
 307 }
 308 EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
 309
 310 void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 311         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 312                 udelay(100);
 313         else
 314                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 315 }
 316 EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
 317
 318 void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
 319         if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
 320                 udelay(400);
 321         else
 322                 mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
 323 }
 324 EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
 325
 326 u8 drm_dp_link_rate_to_bw_code(int link_rate)
 327 {
 328         switch (link_rate) {
 329         case 162000:
 330         default:
 331                 return DP_LINK_BW_1_62;
 332         case 270000:
 333                 return DP_LINK_BW_2_7;
 334         case 540000:
 335                 return DP_LINK_BW_5_4;
 336         }
 337 }
 338 EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code);
 339
 340 int drm_dp_bw_code_to_link_rate(u8 link_bw)
 341 {
 342         switch (link_bw) {
 343         case DP_LINK_BW_1_62:
 344         default:
 345                 return 162000;
 346         case DP_LINK_BW_2_7:
 347                 return 270000;
 348         case DP_LINK_BW_5_4:
 349                 return 540000;
 350         }
 351 }
 352 EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
 353
 354 /**
 355  * DOC: dp helpers
 356  *
 357  * The DisplayPort AUX channel is an abstraction to allow generic, driver-
 358  * independent access to AUX functionality. Drivers can take advantage of
 359  * this by filling in the fields of the drm_dp_aux structure.
 360  *
 361  * Transactions are described using a hardware-independent drm_dp_aux_msg
 362  * structure, which is passed into a driver's .transfer() implementation.
 363  * Both native and I2C-over-AUX transactions are supported.
 364  */
 365
 366 static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 367                               unsigned int offset, void *buffer, size_t size)
 368 {
 369         struct drm_dp_aux_msg msg;
 370         unsigned int retry;
 371         int err;
 372
 373         memset(&msg, 0, sizeof(msg));
 374         msg.address = offset;
 375         msg.request = request;
 376         msg.buffer = buffer;
 377         msg.size = size;
 378
 379         /*
 380          * The specification doesn't give any recommendation on how often to
 381          * retry native transactions, so retry 7 times like for I2C-over-AUX
 382          * transactions.
 383          */
 384         for (retry = 0; retry < 7; retry++) {
 385
 386                 mutex_lock(&aux->hw_mutex);
 387                 err = aux->transfer(aux, &msg);
 388                 mutex_unlock(&aux->hw_mutex);
 389                 if (err < 0) {
 390                         if (err == -EBUSY)
 391                                 continue;
 392
 393                         return err;
 394                 }
 395
 396
 397                 switch (msg.reply & DP_AUX_NATIVE_REPLY_MASK) {
 398                 case DP_AUX_NATIVE_REPLY_ACK:
 399                         if (err < size)
 400                                 return -EPROTO;
 401                         return err;
 402
 403                 case DP_AUX_NATIVE_REPLY_NACK:
 404                         return -EIO;
 405
 406                 case DP_AUX_NATIVE_REPLY_DEFER:
 407                         usleep_range(400, 500);
 408                         break;
 409                 }
 410         }
 411
 412         DRM_DEBUG_KMS("too many retries, giving up\n");
 413         return -EIO;
 414 }
 415
 416 /**
 417  * drm_dp_dpcd_read() - read a series of bytes from the DPCD
 418  * @aux: DisplayPort AUX channel
 419  * @offset: address of the (first) register to read
 420  * @buffer: buffer to store the register values
 421  * @size: number of bytes in @buffer
 422  *
 423  * Returns the number of bytes transferred on success, or a negative error
 424  * code on failure. -EIO is returned if the request was NAKed by the sink or
 425  * if the retry count was exceeded. If not all bytes were transferred, this
 426  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 427  * function, with the exception of -EBUSY (which causes the transaction to
 428  * be retried), are propagated to the caller.
 429  */
 430 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
 431                          void *buffer, size_t size)
 432 {
 433         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_READ, offset, buffer,
 434                                   size);
 435 }
 436 EXPORT_SYMBOL(drm_dp_dpcd_read);
 437
 438 /**
 439  * drm_dp_dpcd_write() - write a series of bytes to the DPCD
 440  * @aux: DisplayPort AUX channel
 441  * @offset: address of the (first) register to write
 442  * @buffer: buffer containing the values to write
 443  * @size: number of bytes in @buffer
 444  *
 445  * Returns the number of bytes transferred on success, or a negative error
 446  * code on failure. -EIO is returned if the request was NAKed by the sink or
 447  * if the retry count was exceeded. If not all bytes were transferred, this
 448  * function returns -EPROTO. Errors from the underlying AUX channel transfer
 449  * function, with the exception of -EBUSY (which causes the transaction to
 450  * be retried), are propagated to the caller.
 451  */
 452 ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
 453                           void *buffer, size_t size)
 454 {
 455         return drm_dp_dpcd_access(aux, DP_AUX_NATIVE_WRITE, offset, buffer,
 456                                   size);
 457 }
 458 EXPORT_SYMBOL(drm_dp_dpcd_write);
 459
 460 /**
 461  * drm_dp_dpcd_read_link_status() - read DPCD link status (bytes 0x202-0x207)
 462  * @aux: DisplayPort AUX channel
 463  * @status: buffer to store the link status in (must be at least 6 bytes)
 464  *
 465  * Returns the number of bytes transferred on success or a negative error
 466  * code on failure.
 467  */
 468 int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux,
 469                                  u8 status[DP_LINK_STATUS_SIZE])
 470 {
 471         return drm_dp_dpcd_read(aux, DP_LANE0_1_STATUS, status,
 472                                 DP_LINK_STATUS_SIZE);
 473 }
 474 EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
 475
 476 /**
 477  * drm_dp_link_probe() - probe a DisplayPort link for capabilities
 478  * @aux: DisplayPort AUX channel
 479  * @link: pointer to structure in which to return link capabilities
 480  *
 481  * The structure filled in by this function can usually be passed directly
 482  * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and
 483  * configure the link based on the link's capabilities.
 484  *
 485  * Returns 0 on success or a negative error code on failure.
 486  */
 487 int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
 488 {
 489         u8 values[3];
 490         int err;
 491
 492         memset(link, 0, sizeof(*link));
 493
 494         err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));
 495         if (err < 0)
 496                 return err;
 497
 498         link->revision = values[0];
 499         link->rate = drm_dp_bw_code_to_link_rate(values[1]);
 500         link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK;
 501
 502         if (values[2] & DP_ENHANCED_FRAME_CAP)
 503                 link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;
 504
 505         return 0;
 506 }
 507 EXPORT_SYMBOL(drm_dp_link_probe);
 508
 509 /**
 510  * drm_dp_link_power_up() - power up a DisplayPort link
 511  * @aux: DisplayPort AUX channel
 512  * @link: pointer to a structure containing the link configuration
 513  *
 514  * Returns 0 on success or a negative error code on failure.
 515  */
 516 int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
 517 {
 518         u8 value;
 519         int err;
 520
 521         /* DP_SET_POWER register is only available on DPCD v1.1 and later */
 522         if (link->revision < 0x11)
 523                 return 0;
 524
 525         err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
 526         if (err < 0)
 527                 return err;
 528
 529         value &= ~DP_SET_POWER_MASK;
 530         value |= DP_SET_POWER_D0;
 531
 532         err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
 533         if (err < 0)
 534                 return err;
 535
 536         /*
 537          * According to the DP 1.1 specification, a "Sink Device must exit the
 538          * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
 539          * Control Field" (register 0x600).
 540          */
 541         usleep_range(1000, 2000);
 542
 543         return 0;
 544 }
 545 EXPORT_SYMBOL(drm_dp_link_power_up);
 546
 547 /**
 548  * drm_dp_link_configure() - configure a DisplayPort link
 549  * @aux: DisplayPort AUX channel
 550  * @link: pointer to a structure containing the link configuration
 551  *
 552  * Returns 0 on success or a negative error code on failure.
 553  */
 554 int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
 555 {
 556         u8 values[2];
 557         int err;
 558
 559         values[0] = drm_dp_link_rate_to_bw_code(link->rate);
 560         values[1] = link->num_lanes;
 561
 562         if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)
 563                 values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
 564
 565         err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));
 566         if (err < 0)
 567                 return err;
 568
 569         return 0;
 570 }
 571 EXPORT_SYMBOL(drm_dp_link_configure);
 572
 573 /*
 574  * I2C-over-AUX implementation
 575  */
 576
 577 static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
 578 {
 579         return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
 580                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 581                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 582                I2C_FUNC_10BIT_ADDR;
 583 }
 584
 585 /*
 586  * Transfer a single I2C-over-AUX message and handle various error conditions,
 587  * retrying the transaction as appropriate.  It is assumed that the
 588  * aux->transfer function does not modify anything in the msg other than the
 589  * reply field.
 590  */
 591 static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 592 {
 593         unsigned int retry;
 594         int err;
 595
 596         /*
 597          * DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
 598          * is required to retry at least seven times upon receiving AUX_DEFER
 599          * before giving up the AUX transaction.
 600          */
 601         for (retry = 0; retry < 7; retry++) {
 602                 mutex_lock(&aux->hw_mutex);
 603                 err = aux->transfer(aux, msg);
 604                 mutex_unlock(&aux->hw_mutex);
 605                 if (err < 0) {
 606                         if (err == -EBUSY)
 607                                 continue;
 608
 609                         DRM_DEBUG_KMS("transaction failed: %d\n", err);
 610                         return err;
 611                 }
 612
 613
 614                 switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
 615                 case DP_AUX_NATIVE_REPLY_ACK:
 616                         /*
 617                          * For I2C-over-AUX transactions this isn't enough, we
 618                          * need to check for the I2C ACK reply.
 619                          */
 620                         break;
 621
 622                 case DP_AUX_NATIVE_REPLY_NACK:
 623                         DRM_DEBUG_KMS("native nack\n");
 624                         return -EREMOTEIO;
 625
 626                 case DP_AUX_NATIVE_REPLY_DEFER:
 627                         DRM_DEBUG_KMS("native defer");
 628                         /*
 629                          * We could check for I2C bit rate capabilities and if
 630                          * available adjust this interval. We could also be
 631                          * more careful with DP-to-legacy adapters where a
 632                          * long legacy cable may force very low I2C bit rates.
 633                          *
 634                          * For now just defer for long enough to hopefully be
 635                          * safe for all use-cases.
 636                          */
 637                         usleep_range(500, 600);
 638                         continue;
 639
 640                 default:
 641                         DRM_ERROR("invalid native reply %#04x\n", msg->reply);
 642                         return -EREMOTEIO;
 643                 }
 644
 645                 switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
 646                 case DP_AUX_I2C_REPLY_ACK:
 647                         /*
 648                          * Both native ACK and I2C ACK replies received. We
 649                          * can assume the transfer was successful.
 650                          */
 651                         if (err < msg->size)
 652                                 return -EPROTO;
 653                         return 0;
 654
 655                 case DP_AUX_I2C_REPLY_NACK:
 656                         DRM_DEBUG_KMS("I2C nack\n");
 657                         return -EREMOTEIO;
 658
 659                 case DP_AUX_I2C_REPLY_DEFER:
 660                         DRM_DEBUG_KMS("I2C defer\n");
 661                         usleep_range(400, 500);
 662                         continue;
 663
 664                 default:
 665                         DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
 666                         return -EREMOTEIO;
 667                 }
 668         }
 669
 670         DRM_DEBUG_KMS("too many retries, giving up\n");
 671         return -EREMOTEIO;
 672 }
 673
 674 static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 675                            int num)
 676 {
 677         struct drm_dp_aux *aux = adapter->algo_data;
 678         unsigned int i, j;
 679         struct drm_dp_aux_msg msg;
 680         int err = 0;
 681
 682         memset(&msg, 0, sizeof(msg));
 683
 684         for (i = 0; i < num; i++) {
 685                 msg.address = msgs[i].addr;
 686                 msg.request = (msgs[i].flags & I2C_M_RD) ?
 687                         DP_AUX_I2C_READ :
 688                         DP_AUX_I2C_WRITE;
 689                 msg.request |= DP_AUX_I2C_MOT;
 690                 /* Send a bare address packet to start the transaction.
 691                  * Zero sized messages specify an address only (bare
 692                  * address) transaction.
 693                  */
 694                 msg.buffer = NULL;
 695                 msg.size = 0;
 696                 err = drm_dp_i2c_do_msg(aux, &msg);
 697                 if (err < 0)
 698                         break;
 699                 /*
 700                  * Many hardware implementations support FIFOs larger than a
 701                  * single byte, but it has been empirically determined that
 702                  * transferring data in larger chunks can actually lead to
 703                  * decreased performance. Therefore each message is simply
 704                  * transferred byte-by-byte.
 705                  */
 706                 for (j = 0; j < msgs[i].len; j++) {
 707                         msg.buffer = msgs[i].buf + j;
 708                         msg.size = 1;
 709
 710                         err = drm_dp_i2c_do_msg(aux, &msg);
 711                         if (err < 0)
 712                                 break;
 713                 }
 714                 if (err < 0)
 715                         break;
 716         }
 717         if (err >= 0)
 718                 err = num;
 719         /* Send a bare address packet to close out the transaction.
 720          * Zero sized messages specify an address only (bare
 721          * address) transaction.
 722          */
 723         msg.request &= ~DP_AUX_I2C_MOT;
 724         msg.buffer = NULL;
 725         msg.size = 0;
 726         (void)drm_dp_i2c_do_msg(aux, &msg);
 727
 728         return err;
 729 }
 730
 731 static const struct i2c_algorithm drm_dp_i2c_algo = {
 732         .functionality = drm_dp_i2c_functionality,
 733         .master_xfer = drm_dp_i2c_xfer,
 734 };
 735
 736 /**
 737  * drm_dp_aux_register() - initialise and register aux channel
 738  * @aux: DisplayPort AUX channel
 739  *
 740  * Returns 0 on success or a negative error code on failure.
 741  */
 742 int drm_dp_aux_register(struct drm_dp_aux *aux)
 743 {
 744         mutex_init(&aux->hw_mutex);
 745
 746         aux->ddc.algo = &drm_dp_i2c_algo;
 747         aux->ddc.algo_data = aux;
 748         aux->ddc.retries = 3;
 749
 750         aux->ddc.class = I2C_CLASS_DDC;
 751         aux->ddc.owner = THIS_MODULE;
 752         aux->ddc.dev.parent = aux->dev;
 753         aux->ddc.dev.of_node = aux->dev->of_node;
 754
 755         strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
 756                 sizeof(aux->ddc.name));
 757
 758         return i2c_add_adapter(&aux->ddc);
 759 }
 760 EXPORT_SYMBOL(drm_dp_aux_register);
 761
 762 /**
 763  * drm_dp_aux_unregister() - unregister an AUX adapter
 764  * @aux: DisplayPort AUX channel
 765  */
 766 void drm_dp_aux_unregister(struct drm_dp_aux *aux)
 767 {
 768         i2c_del_adapter(&aux->ddc);
 769 }
 770 EXPORT_SYMBOL(drm_dp_aux_unregister);