drivers/i2c/algos/i2c-algo-bit.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * i2c-algo-bit.c: i2c driver algorithms for bit-shift adapters
   4  *
   5  *   Copyright (C) 1995-2000 Simon G. Vogl
   6  *
   7  * With some changes from Frodo Looijaard <frodol@dds.nl>, Kyösti Mälkki
   8  * <kmalkki@cc.hut.fi> and Jean Delvare <jdelvare@suse.de>
   9  */
  10
  11 #include <linux/kernel.h>
  12 #include <linux/module.h>
  13 #include <linux/delay.h>
  14 #include <linux/errno.h>
  15 #include <linux/sched.h>
  16 #include <linux/i2c.h>
  17 #include <linux/i2c-algo-bit.h>
  18
  19
  20 /* ----- global defines ----------------------------------------------- */
  21
  22 #ifdef DEBUG
  23 #define bit_dbg(level, dev, format, args...) \
  24         do { \
  25                 if (i2c_debug >= level) \
  26                         dev_dbg(dev, format, ##args); \
  27         } while (0)
  28 #else
  29 #define bit_dbg(level, dev, format, args...) \
  30         do {} while (0)
  31 #endif /* DEBUG */
  32
  33 /* ----- global variables --------------------------------------------- */
  34
  35 static int bit_test;    /* see if the line-setting functions work       */
  36 module_param(bit_test, int, S_IRUGO);
  37 MODULE_PARM_DESC(bit_test, "lines testing - 0 off; 1 report; 2 fail if stuck");
  38
  39 #ifdef DEBUG
  40 static int i2c_debug = 1;
  41 module_param(i2c_debug, int, S_IRUGO | S_IWUSR);
  42 MODULE_PARM_DESC(i2c_debug,
  43                  "debug level - 0 off; 1 normal; 2 verbose; 3 very verbose");
  44 #endif
  45
  46 /* --- setting states on the bus with the right timing: --------------- */
  47
  48 #define setsda(adap, val)       adap->setsda(adap->data, val)
  49 #define setscl(adap, val)       adap->setscl(adap->data, val)
  50 #define getsda(adap)            adap->getsda(adap->data)
  51 #define getscl(adap)            adap->getscl(adap->data)
  52
  53 static inline void sdalo(struct i2c_algo_bit_data *adap)
  54 {
  55         setsda(adap, 0);
  56         udelay((adap->udelay + 1) / 2);
  57 }
  58
  59 static inline void sdahi(struct i2c_algo_bit_data *adap)
  60 {
  61         setsda(adap, 1);
  62         udelay((adap->udelay + 1) / 2);
  63 }
  64
  65 static inline void scllo(struct i2c_algo_bit_data *adap)
  66 {
  67         setscl(adap, 0);
  68         udelay(adap->udelay / 2);
  69 }
  70
  71 /*
  72  * Raise scl line, and do checking for delays. This is necessary for slower
  73  * devices.
  74  */
  75 static int sclhi(struct i2c_algo_bit_data *adap)
  76 {
  77         unsigned long start;
  78
  79         setscl(adap, 1);
  80
  81         /* Not all adapters have scl sense line... */
  82         if (!adap->getscl)
  83                 goto done;
  84
  85         start = jiffies;
  86         while (!getscl(adap)) {
  87                 /* This hw knows how to read the clock line, so we wait
  88                  * until it actually gets high.  This is safer as some
  89                  * chips may hold it low ("clock stretching") while they
  90                  * are processing data internally.
  91                  */
  92                 if (time_after(jiffies, start + adap->timeout)) {
  93                         /* Test one last time, as we may have been preempted
  94                          * between last check and timeout test.
  95                          */
  96                         if (getscl(adap))
  97                                 break;
  98                         return -ETIMEDOUT;
  99                 }
 100                 cpu_relax();
 101         }
 102 #ifdef DEBUG
 103         if (jiffies != start && i2c_debug >= 3)
 104                 pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go high\n",
 105                          jiffies - start);
 106 #endif
 107
 108 done:
 109         udelay(adap->udelay);
 110         return 0;
 111 }
 112
 113
 114 /* --- other auxiliary functions -------------------------------------- */
 115 static void i2c_start(struct i2c_algo_bit_data *adap)
 116 {
 117         /* assert: scl, sda are high */
 118         setsda(adap, 0);
 119         udelay(adap->udelay);
 120         scllo(adap);
 121 }
 122
 123 static void i2c_repstart(struct i2c_algo_bit_data *adap)
 124 {
 125         /* assert: scl is low */
 126         sdahi(adap);
 127         sclhi(adap);
 128         setsda(adap, 0);
 129         udelay(adap->udelay);
 130         scllo(adap);
 131 }
 132
 133
 134 static void i2c_stop(struct i2c_algo_bit_data *adap)
 135 {
 136         /* assert: scl is low */
 137         sdalo(adap);
 138         sclhi(adap);
 139         setsda(adap, 1);
 140         udelay(adap->udelay);
 141 }
 142
 143
 144
 145 /* send a byte without start cond., look for arbitration,
 146    check ackn. from slave */
 147 /* returns:
 148  * 1 if the device acknowledged
 149  * 0 if the device did not ack
 150  * -ETIMEDOUT if an error occurred (while raising the scl line)
 151  */
 152 static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c)
 153 {
 154         int i;
 155         int sb;
 156         int ack;
 157         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 158
 159         /* assert: scl is low */
 160         for (i = 7; i >= 0; i--) {
 161                 sb = (c >> i) & 1;
 162                 setsda(adap, sb);
 163                 udelay((adap->udelay + 1) / 2);
 164                 if (sclhi(adap) < 0) { /* timed out */
 165                         bit_dbg(1, &i2c_adap->dev,
 166                                 "i2c_outb: 0x%02x, timeout at bit #%d\n",
 167                                 (int)c, i);
 168                         return -ETIMEDOUT;
 169                 }
 170                 /* FIXME do arbitration here:
 171                  * if (sb && !getsda(adap)) -> ouch! Get out of here.
 172                  *
 173                  * Report a unique code, so higher level code can retry
 174                  * the whole (combined) message and *NOT* issue STOP.
 175                  */
 176                 scllo(adap);
 177         }
 178         sdahi(adap);
 179         if (sclhi(adap) < 0) { /* timeout */
 180                 bit_dbg(1, &i2c_adap->dev,
 181                         "i2c_outb: 0x%02x, timeout at ack\n", (int)c);
 182                 return -ETIMEDOUT;
 183         }
 184
 185         /* read ack: SDA should be pulled down by slave, or it may
 186          * NAK (usually to report problems with the data we wrote).
 187          * Always report ACK if SDA is write-only.
 188          */
 189         ack = !adap->getsda || !getsda(adap);    /* ack: sda is pulled low -> success */
 190         bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
 191                 ack ? "A" : "NA");
 192
 193         scllo(adap);
 194         return ack;
 195         /* assert: scl is low (sda undef) */
 196 }
 197
 198
 199 static int i2c_inb(struct i2c_adapter *i2c_adap)
 200 {
 201         /* read byte via i2c port, without start/stop sequence  */
 202         /* acknowledge is sent in i2c_read.                     */
 203         int i;
 204         unsigned char indata = 0;
 205         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 206
 207         /* assert: scl is low */
 208         sdahi(adap);
 209         for (i = 0; i < 8; i++) {
 210                 if (sclhi(adap) < 0) { /* timeout */
 211                         bit_dbg(1, &i2c_adap->dev,
 212                                 "i2c_inb: timeout at bit #%d\n",
 213                                 7 - i);
 214                         return -ETIMEDOUT;
 215                 }
 216                 indata *= 2;
 217                 if (getsda(adap))
 218                         indata |= 0x01;
 219                 setscl(adap, 0);
 220                 udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
 221         }
 222         /* assert: scl is low */
 223         return indata;
 224 }
 225
 226 /*
 227  * Sanity check for the adapter hardware - check the reaction of
 228  * the bus lines only if it seems to be idle.
 229  */
 230 static int test_bus(struct i2c_adapter *i2c_adap)
 231 {
 232         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 233         const char *name = i2c_adap->name;
 234         int scl, sda, ret;
 235
 236         if (adap->pre_xfer) {
 237                 ret = adap->pre_xfer(i2c_adap);
 238                 if (ret < 0)
 239                         return -ENODEV;
 240         }
 241
 242         if (adap->getsda == NULL)
 243                 pr_info("%s: SDA is write-only, testing not possible\n", name);
 244         if (adap->getscl == NULL)
 245                 pr_info("%s: SCL is write-only, testing not possible\n", name);
 246
 247         sda = adap->getsda ? getsda(adap) : 1;
 248         scl = adap->getscl ? getscl(adap) : 1;
 249         if (!scl || !sda) {
 250                 pr_warn("%s: bus seems to be busy (scl=%d, sda=%d)\n", name, scl, sda);
 251                 goto bailout;
 252         }
 253
 254         sdalo(adap);
 255         if (adap->getsda && getsda(adap)) {
 256                 pr_warn("%s: SDA stuck high!\n", name);
 257                 goto bailout;
 258         }
 259         if (adap->getscl && !getscl(adap)) {
 260                 pr_warn("%s: SCL unexpected low while pulling SDA low!\n", name);
 261                 goto bailout;
 262         }
 263
 264         sdahi(adap);
 265         if (adap->getsda && !getsda(adap)) {
 266                 pr_warn("%s: SDA stuck low!\n", name);
 267                 goto bailout;
 268         }
 269         if (adap->getscl && !getscl(adap)) {
 270                 pr_warn("%s: SCL unexpected low while pulling SDA high!\n", name);
 271                 goto bailout;
 272         }
 273
 274         scllo(adap);
 275         if (adap->getscl && getscl(adap)) {
 276                 pr_warn("%s: SCL stuck high!\n", name);
 277                 goto bailout;
 278         }
 279         if (adap->getsda && !getsda(adap)) {
 280                 pr_warn("%s: SDA unexpected low while pulling SCL low!\n", name);
 281                 goto bailout;
 282         }
 283
 284         sclhi(adap);
 285         if (adap->getscl && !getscl(adap)) {
 286                 pr_warn("%s: SCL stuck low!\n", name);
 287                 goto bailout;
 288         }
 289         if (adap->getsda && !getsda(adap)) {
 290                 pr_warn("%s: SDA unexpected low while pulling SCL high!\n", name);
 291                 goto bailout;
 292         }
 293
 294         if (adap->post_xfer)
 295                 adap->post_xfer(i2c_adap);
 296
 297         pr_info("%s: Test OK\n", name);
 298         return 0;
 299 bailout:
 300         sdahi(adap);
 301         sclhi(adap);
 302
 303         if (adap->post_xfer)
 304                 adap->post_xfer(i2c_adap);
 305
 306         return -ENODEV;
 307 }
 308
 309 /* ----- Utility functions
 310  */
 311
 312 /* try_address tries to contact a chip for a number of
 313  * times before it gives up.
 314  * return values:
 315  * 1 chip answered
 316  * 0 chip did not answer
 317  * -x transmission error
 318  */
 319 static int try_address(struct i2c_adapter *i2c_adap,
 320                        unsigned char addr, int retries)
 321 {
 322         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 323         int i, ret = 0;
 324
 325         for (i = 0; i <= retries; i++) {
 326                 ret = i2c_outb(i2c_adap, addr);
 327                 if (ret == 1 || i == retries)
 328                         break;
 329                 bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 330                 i2c_stop(adap);
 331                 udelay(adap->udelay);
 332                 yield();
 333                 bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 334                 i2c_start(adap);
 335         }
 336         if (i && ret)
 337                 bit_dbg(1, &i2c_adap->dev,
 338                         "Used %d tries to %s client at 0x%02x: %s\n", i + 1,
 339                         addr & 1 ? "read from" : "write to", addr >> 1,
 340                         ret == 1 ? "success" : "failed, timeout?");
 341         return ret;
 342 }
 343
 344 static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 345 {
 346         const unsigned char *temp = msg->buf;
 347         int count = msg->len;
 348         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 349         int retval;
 350         int wrcount = 0;
 351
 352         while (count > 0) {
 353                 retval = i2c_outb(i2c_adap, *temp);
 354
 355                 /* OK/ACK; or ignored NAK */
 356                 if ((retval > 0) || (nak_ok && (retval == 0))) {
 357                         count--;
 358                         temp++;
 359                         wrcount++;
 360
 361                 /* A slave NAKing the master means the slave didn't like
 362                  * something about the data it saw.  For example, maybe
 363                  * the SMBus PEC was wrong.
 364                  */
 365                 } else if (retval == 0) {
 366                         dev_err(&i2c_adap->dev, "sendbytes: NAK bailout.\n");
 367                         return -EIO;
 368
 369                 /* Timeout; or (someday) lost arbitration
 370                  *
 371                  * FIXME Lost ARB implies retrying the transaction from
 372                  * the first message, after the "winning" master issues
 373                  * its STOP.  As a rule, upper layer code has no reason
 374                  * to know or care about this ... it is *NOT* an error.
 375                  */
 376                 } else {
 377                         dev_err(&i2c_adap->dev, "sendbytes: error %d\n",
 378                                         retval);
 379                         return retval;
 380                 }
 381         }
 382         return wrcount;
 383 }
 384
 385 static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
 386 {
 387         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 388
 389         /* assert: sda is high */
 390         if (is_ack)             /* send ack */
 391                 setsda(adap, 0);
 392         udelay((adap->udelay + 1) / 2);
 393         if (sclhi(adap) < 0) {  /* timeout */
 394                 dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
 395                 return -ETIMEDOUT;
 396         }
 397         scllo(adap);
 398         return 0;
 399 }
 400
 401 static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 402 {
 403         int inval;
 404         int rdcount = 0;        /* counts bytes read */
 405         unsigned char *temp = msg->buf;
 406         int count = msg->len;
 407         const unsigned flags = msg->flags;
 408         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 409
 410         if (!adap->getsda)
 411                 return -EOPNOTSUPP;
 412
 413         while (count > 0) {
 414                 inval = i2c_inb(i2c_adap);
 415                 if (inval >= 0) {
 416                         *temp = inval;
 417                         rdcount++;
 418                 } else {   /* read timed out */
 419                         break;
 420                 }
 421
 422                 temp++;
 423                 count--;
 424
 425                 /* Some SMBus transactions require that we receive the
 426                    transaction length as the first read byte. */
 427                 if (rdcount == 1 && (flags & I2C_M_RECV_LEN)) {
 428                         if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
 429                                 if (!(flags & I2C_M_NO_RD_ACK))
 430                                         acknak(i2c_adap, 0);
 431                                 dev_err(&i2c_adap->dev,
 432                                         "readbytes: invalid block length (%d)\n",
 433                                         inval);
 434                                 return -EPROTO;
 435                         }
 436                         /* The original count value accounts for the extra
 437                            bytes, that is, either 1 for a regular transaction,
 438                            or 2 for a PEC transaction. */
 439                         count += inval;
 440                         msg->len += inval;
 441                 }
 442
 443                 bit_dbg(2, &i2c_adap->dev, "readbytes: 0x%02x %s\n",
 444                         inval,
 445                         (flags & I2C_M_NO_RD_ACK)
 446                                 ? "(no ack/nak)"
 447                                 : (count ? "A" : "NA"));
 448
 449                 if (!(flags & I2C_M_NO_RD_ACK)) {
 450                         inval = acknak(i2c_adap, count);
 451                         if (inval < 0)
 452                                 return inval;
 453                 }
 454         }
 455         return rdcount;
 456 }
 457
 458 /* doAddress initiates the transfer by generating the start condition (in
 459  * try_address) and transmits the address in the necessary format to handle
 460  * reads, writes as well as 10bit-addresses.
 461  * returns:
 462  *  0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
 463  * -x an error occurred (like: -ENXIO if the device did not answer, or
 464  *      -ETIMEDOUT, for example if the lines are stuck...)
 465  */
 466 static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 467 {
 468         unsigned short flags = msg->flags;
 469         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 470         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 471
 472         unsigned char addr;
 473         int ret, retries;
 474
 475         retries = nak_ok ? 0 : i2c_adap->retries;
 476
 477         if (flags & I2C_M_TEN) {
 478                 /* a ten bit address */
 479                 addr = 0xf0 | ((msg->addr >> 7) & 0x06);
 480                 bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
 481                 /* try extended address code...*/
 482                 ret = try_address(i2c_adap, addr, retries);
 483                 if ((ret != 1) && !nak_ok)  {
 484                         dev_err(&i2c_adap->dev,
 485                                 "died at extended address code\n");
 486                         return -ENXIO;
 487                 }
 488                 /* the remaining 8 bit address */
 489                 ret = i2c_outb(i2c_adap, msg->addr & 0xff);
 490                 if ((ret != 1) && !nak_ok) {
 491                         /* the chip did not ack / xmission error occurred */
 492                         dev_err(&i2c_adap->dev, "died at 2nd address code\n");
 493                         return -ENXIO;
 494                 }
 495                 if (flags & I2C_M_RD) {
 496                         bit_dbg(3, &i2c_adap->dev,
 497                                 "emitting repeated start condition\n");
 498                         i2c_repstart(adap);
 499                         /* okay, now switch into reading mode */
 500                         addr |= 0x01;
 501                         ret = try_address(i2c_adap, addr, retries);
 502                         if ((ret != 1) && !nak_ok) {
 503                                 dev_err(&i2c_adap->dev,
 504                                         "died at repeated address code\n");
 505                                 return -EIO;
 506                         }
 507                 }
 508         } else {                /* normal 7bit address  */
 509                 addr = i2c_8bit_addr_from_msg(msg);
 510                 if (flags & I2C_M_REV_DIR_ADDR)
 511                         addr ^= 1;
 512                 ret = try_address(i2c_adap, addr, retries);
 513                 if ((ret != 1) && !nak_ok)
 514                         return -ENXIO;
 515         }
 516
 517         return 0;
 518 }
 519
 520 static int bit_xfer(struct i2c_adapter *i2c_adap,
 521                     struct i2c_msg msgs[], int num)
 522 {
 523         struct i2c_msg *pmsg;
 524         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 525         int i, ret;
 526         unsigned short nak_ok;
 527
 528         if (adap->pre_xfer) {
 529                 ret = adap->pre_xfer(i2c_adap);
 530                 if (ret < 0)
 531                         return ret;
 532         }
 533
 534         bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 535         i2c_start(adap);
 536         for (i = 0; i < num; i++) {
 537                 pmsg = &msgs[i];
 538                 nak_ok = pmsg->flags & I2C_M_IGNORE_NAK;
 539                 if (!(pmsg->flags & I2C_M_NOSTART)) {
 540                         if (i) {
 541                                 if (msgs[i - 1].flags & I2C_M_STOP) {
 542                                         bit_dbg(3, &i2c_adap->dev,
 543                                                 "emitting enforced stop/start condition\n");
 544                                         i2c_stop(adap);
 545                                         i2c_start(adap);
 546                                 } else {
 547                                         bit_dbg(3, &i2c_adap->dev,
 548                                                 "emitting repeated start condition\n");
 549                                         i2c_repstart(adap);
 550                                 }
 551                         }
 552                         ret = bit_doAddress(i2c_adap, pmsg);
 553                         if ((ret != 0) && !nak_ok) {
 554                                 bit_dbg(1, &i2c_adap->dev,
 555                                         "NAK from device addr 0x%02x msg #%d\n",
 556                                         msgs[i].addr, i);
 557                                 goto bailout;
 558                         }
 559                 }
 560                 if (pmsg->flags & I2C_M_RD) {
 561                         /* read bytes into buffer*/
 562                         ret = readbytes(i2c_adap, pmsg);
 563                         if (ret >= 1)
 564                                 bit_dbg(2, &i2c_adap->dev, "read %d byte%s\n",
 565                                         ret, ret == 1 ? "" : "s");
 566                         if (ret < pmsg->len) {
 567                                 if (ret >= 0)
 568                                         ret = -EIO;
 569                                 goto bailout;
 570                         }
 571                 } else {
 572                         /* write bytes from buffer */
 573                         ret = sendbytes(i2c_adap, pmsg);
 574                         if (ret >= 1)
 575                                 bit_dbg(2, &i2c_adap->dev, "wrote %d byte%s\n",
 576                                         ret, ret == 1 ? "" : "s");
 577                         if (ret < pmsg->len) {
 578                                 if (ret >= 0)
 579                                         ret = -EIO;
 580                                 goto bailout;
 581                         }
 582                 }
 583         }
 584         ret = i;
 585
 586 bailout:
 587         bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 588         i2c_stop(adap);
 589
 590         if (adap->post_xfer)
 591                 adap->post_xfer(i2c_adap);
 592         return ret;
 593 }
 594
 595 /*
 596  * We print a warning when we are not flagged to support atomic transfers but
 597  * will try anyhow. That's what the I2C core would do as well. Sadly, we can't
 598  * modify the algorithm struct at probe time because this struct is exported
 599  * 'const'.
 600  */
 601 static int bit_xfer_atomic(struct i2c_adapter *i2c_adap, struct i2c_msg msgs[],
 602                            int num)
 603 {
 604         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 605
 606         if (!adap->can_do_atomic)
 607                 dev_warn(&i2c_adap->dev, "not flagged for atomic transfers\n");
 608
 609         return bit_xfer(i2c_adap, msgs, num);
 610 }
 611
 612 static u32 bit_func(struct i2c_adapter *adap)
 613 {
 614         return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL_ALL |
 615                I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
 616 }
 617
 618
 619 /* -----exported algorithm data: -------------------------------------  */
 620
 621 const struct i2c_algorithm i2c_bit_algo = {
 622         .master_xfer = bit_xfer,
 623         .master_xfer_atomic = bit_xfer_atomic,
 624         .functionality = bit_func,
 625 };
 626 EXPORT_SYMBOL(i2c_bit_algo);
 627
 628 static const struct i2c_adapter_quirks i2c_bit_quirk_no_clk_stretch = {
 629         .flags = I2C_AQ_NO_CLK_STRETCH,
 630 };
 631
 632 /*
 633  * registering functions to load algorithms at runtime
 634  */
 635 static int __i2c_bit_add_bus(struct i2c_adapter *adap,
 636                              int (*add_adapter)(struct i2c_adapter *))
 637 {
 638         struct i2c_algo_bit_data *bit_adap = adap->algo_data;
 639         int ret;
 640
 641         if (bit_test) {
 642                 ret = test_bus(adap);
 643                 if (bit_test >= 2 && ret < 0)
 644                         return -ENODEV;
 645         }
 646
 647         /* register new adapter to i2c module... */
 648         adap->algo = &i2c_bit_algo;
 649         adap->retries = 3;
 650         if (bit_adap->getscl == NULL)
 651                 adap->quirks = &i2c_bit_quirk_no_clk_stretch;
 652
 653         /*
 654          * We tried forcing SCL/SDA to an initial state here. But that caused a
 655          * regression, sadly. Check Bugzilla #200045 for details.
 656          */
 657
 658         ret = add_adapter(adap);
 659         if (ret < 0)
 660                 return ret;
 661
 662         if (bit_adap->getsda == NULL)
 663                 dev_warn(&adap->dev, "Not I2C compliant: can't read SDA\n");
 664
 665         if (bit_adap->getscl == NULL)
 666                 dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
 667
 668         if (bit_adap->getsda == NULL || bit_adap->getscl == NULL)
 669                 dev_warn(&adap->dev, "Bus may be unreliable\n");
 670
 671         return 0;
 672 }
 673
 674 int i2c_bit_add_bus(struct i2c_adapter *adap)
 675 {
 676         return __i2c_bit_add_bus(adap, i2c_add_adapter);
 677 }
 678 EXPORT_SYMBOL(i2c_bit_add_bus);
 679
 680 int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
 681 {
 682         return __i2c_bit_add_bus(adap, i2c_add_numbered_adapter);
 683 }
 684 EXPORT_SYMBOL(i2c_bit_add_numbered_bus);
 685
 686 MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
 687 MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
 688 MODULE_LICENSE("GPL");