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

   1 /* -------------------------------------------------------------------------
   2  * i2c-algo-bit.c i2c driver algorithms for bit-shift adapters
   3  * -------------------------------------------------------------------------
   4  *   Copyright (C) 1995-2000 Simon G. Vogl
   5
   6     This program is free software; you can redistribute it and/or modify
   7     it under the terms of the GNU General Public License as published by
   8     the Free Software Foundation; either version 2 of the License, or
   9     (at your option) any later version.
  10
  11     This program is distributed in the hope that it will be useful,
  12     but WITHOUT ANY WARRANTY; without even the implied warranty of
  13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14     GNU General Public License for more details.
  15  * ------------------------------------------------------------------------- */
  16
  17 /* With some changes from Frodo Looijaard <[email protected]>, Kyösti Mälkki
  18    <[email protected]> and Jean Delvare <[email protected]> */
  19
  20 #include <linux/kernel.h>
  21 #include <linux/module.h>
  22 #include <linux/delay.h>
  23 #include <linux/errno.h>
  24 #include <linux/sched.h>
  25 #include <linux/i2c.h>
  26 #include <linux/i2c-algo-bit.h>
  27
  28
  29 /* ----- global defines ----------------------------------------------- */
  30
  31 #ifdef DEBUG
  32 #define bit_dbg(level, dev, format, args...) \
  33         do { \
  34                 if (i2c_debug >= level) \
  35                         dev_dbg(dev, format, ##args); \
  36         } while (0)
  37 #else
  38 #define bit_dbg(level, dev, format, args...) \
  39         do {} while (0)
  40 #endif /* DEBUG */
  41
  42 /* ----- global variables --------------------------------------------- */
  43
  44 static int bit_test;    /* see if the line-setting functions work       */
  45 module_param(bit_test, int, S_IRUGO);
  46 MODULE_PARM_DESC(bit_test, "lines testing - 0 off; 1 report; 2 fail if stuck");
  47
  48 #ifdef DEBUG
  49 static int i2c_debug = 1;
  50 module_param(i2c_debug, int, S_IRUGO | S_IWUSR);
  51 MODULE_PARM_DESC(i2c_debug,
  52                  "debug level - 0 off; 1 normal; 2 verbose; 3 very verbose");
  53 #endif
  54
  55 /* --- setting states on the bus with the right timing: --------------- */
  56
  57 #define setsda(adap, val)       adap->setsda(adap->data, val)
  58 #define setscl(adap, val)       adap->setscl(adap->data, val)
  59 #define getsda(adap)            adap->getsda(adap->data)
  60 #define getscl(adap)            adap->getscl(adap->data)
  61
  62 static inline void sdalo(struct i2c_algo_bit_data *adap)
  63 {
  64         setsda(adap, 0);
  65         udelay((adap->udelay + 1) / 2);
  66 }
  67
  68 static inline void sdahi(struct i2c_algo_bit_data *adap)
  69 {
  70         setsda(adap, 1);
  71         udelay((adap->udelay + 1) / 2);
  72 }
  73
  74 static inline void scllo(struct i2c_algo_bit_data *adap)
  75 {
  76         setscl(adap, 0);
  77         udelay(adap->udelay / 2);
  78 }
  79
  80 /*
  81  * Raise scl line, and do checking for delays. This is necessary for slower
  82  * devices.
  83  */
  84 static int sclhi(struct i2c_algo_bit_data *adap)
  85 {
  86         unsigned long start;
  87
  88         setscl(adap, 1);
  89
  90         /* Not all adapters have scl sense line... */
  91         if (!adap->getscl)
  92                 goto done;
  93
  94         start = jiffies;
  95         while (!getscl(adap)) {
  96                 /* This hw knows how to read the clock line, so we wait
  97                  * until it actually gets high.  This is safer as some
  98                  * chips may hold it low ("clock stretching") while they
  99                  * are processing data internally.
 100                  */
 101                 if (time_after(jiffies, start + adap->timeout)) {
 102                         /* Test one last time, as we may have been preempted
 103                          * between last check and timeout test.
 104                          */
 105                         if (getscl(adap))
 106                                 break;
 107                         return -ETIMEDOUT;
 108                 }
 109                 cpu_relax();
 110         }
 111 #ifdef DEBUG
 112         if (jiffies != start && i2c_debug >= 3)
 113                 pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go high\n",
 114                          jiffies - start);
 115 #endif
 116
 117 done:
 118         udelay(adap->udelay);
 119         return 0;
 120 }
 121
 122
 123 /* --- other auxiliary functions -------------------------------------- */
 124 static void i2c_start(struct i2c_algo_bit_data *adap)
 125 {
 126         /* assert: scl, sda are high */
 127         setsda(adap, 0);
 128         udelay(adap->udelay);
 129         scllo(adap);
 130 }
 131
 132 static void i2c_repstart(struct i2c_algo_bit_data *adap)
 133 {
 134         /* assert: scl is low */
 135         sdahi(adap);
 136         sclhi(adap);
 137         setsda(adap, 0);
 138         udelay(adap->udelay);
 139         scllo(adap);
 140 }
 141
 142
 143 static void i2c_stop(struct i2c_algo_bit_data *adap)
 144 {
 145         /* assert: scl is low */
 146         sdalo(adap);
 147         sclhi(adap);
 148         setsda(adap, 1);
 149         udelay(adap->udelay);
 150 }
 151
 152
 153
 154 /* send a byte without start cond., look for arbitration,
 155    check ackn. from slave */
 156 /* returns:
 157  * 1 if the device acknowledged
 158  * 0 if the device did not ack
 159  * -ETIMEDOUT if an error occurred (while raising the scl line)
 160  */
 161 static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c)
 162 {
 163         int i;
 164         int sb;
 165         int ack;
 166         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 167
 168         /* assert: scl is low */
 169         for (i = 7; i >= 0; i--) {
 170                 sb = (c >> i) & 1;
 171                 setsda(adap, sb);
 172                 udelay((adap->udelay + 1) / 2);
 173                 if (sclhi(adap) < 0) { /* timed out */
 174                         bit_dbg(1, &i2c_adap->dev,
 175                                 "i2c_outb: 0x%02x, timeout at bit #%d\n",
 176                                 (int)c, i);
 177                         return -ETIMEDOUT;
 178                 }
 179                 /* FIXME do arbitration here:
 180                  * if (sb && !getsda(adap)) -> ouch! Get out of here.
 181                  *
 182                  * Report a unique code, so higher level code can retry
 183                  * the whole (combined) message and *NOT* issue STOP.
 184                  */
 185                 scllo(adap);
 186         }
 187         sdahi(adap);
 188         if (sclhi(adap) < 0) { /* timeout */
 189                 bit_dbg(1, &i2c_adap->dev,
 190                         "i2c_outb: 0x%02x, timeout at ack\n", (int)c);
 191                 return -ETIMEDOUT;
 192         }
 193
 194         /* read ack: SDA should be pulled down by slave, or it may
 195          * NAK (usually to report problems with the data we wrote).
 196          */
 197         ack = !getsda(adap);    /* ack: sda is pulled low -> success */
 198         bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
 199                 ack ? "A" : "NA");
 200
 201         scllo(adap);
 202         return ack;
 203         /* assert: scl is low (sda undef) */
 204 }
 205
 206
 207 static int i2c_inb(struct i2c_adapter *i2c_adap)
 208 {
 209         /* read byte via i2c port, without start/stop sequence  */
 210         /* acknowledge is sent in i2c_read.                     */
 211         int i;
 212         unsigned char indata = 0;
 213         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 214
 215         /* assert: scl is low */
 216         sdahi(adap);
 217         for (i = 0; i < 8; i++) {
 218                 if (sclhi(adap) < 0) { /* timeout */
 219                         bit_dbg(1, &i2c_adap->dev,
 220                                 "i2c_inb: timeout at bit #%d\n",
 221                                 7 - i);
 222                         return -ETIMEDOUT;
 223                 }
 224                 indata *= 2;
 225                 if (getsda(adap))
 226                         indata |= 0x01;
 227                 setscl(adap, 0);
 228                 udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
 229         }
 230         /* assert: scl is low */
 231         return indata;
 232 }
 233
 234 /*
 235  * Sanity check for the adapter hardware - check the reaction of
 236  * the bus lines only if it seems to be idle.
 237  */
 238 static int test_bus(struct i2c_adapter *i2c_adap)
 239 {
 240         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 241         const char *name = i2c_adap->name;
 242         int scl, sda, ret;
 243
 244         if (adap->pre_xfer) {
 245                 ret = adap->pre_xfer(i2c_adap);
 246                 if (ret < 0)
 247                         return -ENODEV;
 248         }
 249
 250         if (adap->getscl == NULL)
 251                 pr_info("%s: Testing SDA only, SCL is not readable\n", name);
 252
 253         sda = getsda(adap);
 254         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 255         if (!scl || !sda) {
 256                 printk(KERN_WARNING
 257                        "%s: bus seems to be busy (scl=%d, sda=%d)\n",
 258                        name, scl, sda);
 259                 goto bailout;
 260         }
 261
 262         sdalo(adap);
 263         sda = getsda(adap);
 264         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 265         if (sda) {
 266                 printk(KERN_WARNING "%s: SDA stuck high!\n", name);
 267                 goto bailout;
 268         }
 269         if (!scl) {
 270                 printk(KERN_WARNING
 271                        "%s: SCL unexpected low while pulling SDA low!\n",
 272                        name);
 273                 goto bailout;
 274         }
 275
 276         sdahi(adap);
 277         sda = getsda(adap);
 278         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 279         if (!sda) {
 280                 printk(KERN_WARNING "%s: SDA stuck low!\n", name);
 281                 goto bailout;
 282         }
 283         if (!scl) {
 284                 printk(KERN_WARNING
 285                        "%s: SCL unexpected low while pulling SDA high!\n",
 286                        name);
 287                 goto bailout;
 288         }
 289
 290         scllo(adap);
 291         sda = getsda(adap);
 292         scl = (adap->getscl == NULL) ? 0 : getscl(adap);
 293         if (scl) {
 294                 printk(KERN_WARNING "%s: SCL stuck high!\n", name);
 295                 goto bailout;
 296         }
 297         if (!sda) {
 298                 printk(KERN_WARNING
 299                        "%s: SDA unexpected low while pulling SCL low!\n",
 300                        name);
 301                 goto bailout;
 302         }
 303
 304         sclhi(adap);
 305         sda = getsda(adap);
 306         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 307         if (!scl) {
 308                 printk(KERN_WARNING "%s: SCL stuck low!\n", name);
 309                 goto bailout;
 310         }
 311         if (!sda) {
 312                 printk(KERN_WARNING
 313                        "%s: SDA unexpected low while pulling SCL high!\n",
 314                        name);
 315                 goto bailout;
 316         }
 317
 318         if (adap->post_xfer)
 319                 adap->post_xfer(i2c_adap);
 320
 321         pr_info("%s: Test OK\n", name);
 322         return 0;
 323 bailout:
 324         sdahi(adap);
 325         sclhi(adap);
 326
 327         if (adap->post_xfer)
 328                 adap->post_xfer(i2c_adap);
 329
 330         return -ENODEV;
 331 }
 332
 333 /* ----- Utility functions
 334  */
 335
 336 /* try_address tries to contact a chip for a number of
 337  * times before it gives up.
 338  * return values:
 339  * 1 chip answered
 340  * 0 chip did not answer
 341  * -x transmission error
 342  */
 343 static int try_address(struct i2c_adapter *i2c_adap,
 344                        unsigned char addr, int retries)
 345 {
 346         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 347         int i, ret = 0;
 348
 349         for (i = 0; i <= retries; i++) {
 350                 ret = i2c_outb(i2c_adap, addr);
 351                 if (ret == 1 || i == retries)
 352                         break;
 353                 bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 354                 i2c_stop(adap);
 355                 udelay(adap->udelay);
 356                 yield();
 357                 bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 358                 i2c_start(adap);
 359         }
 360         if (i && ret)
 361                 bit_dbg(1, &i2c_adap->dev,
 362                         "Used %d tries to %s client at 0x%02x: %s\n", i + 1,
 363                         addr & 1 ? "read from" : "write to", addr >> 1,
 364                         ret == 1 ? "success" : "failed, timeout?");
 365         return ret;
 366 }
 367
 368 static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 369 {
 370         const unsigned char *temp = msg->buf;
 371         int count = msg->len;
 372         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 373         int retval;
 374         int wrcount = 0;
 375
 376         while (count > 0) {
 377                 retval = i2c_outb(i2c_adap, *temp);
 378
 379                 /* OK/ACK; or ignored NAK */
 380                 if ((retval > 0) || (nak_ok && (retval == 0))) {
 381                         count--;
 382                         temp++;
 383                         wrcount++;
 384
 385                 /* A slave NAKing the master means the slave didn't like
 386                  * something about the data it saw.  For example, maybe
 387                  * the SMBus PEC was wrong.
 388                  */
 389                 } else if (retval == 0) {
 390                         dev_err(&i2c_adap->dev, "sendbytes: NAK bailout.\n");
 391                         return -EIO;
 392
 393                 /* Timeout; or (someday) lost arbitration
 394                  *
 395                  * FIXME Lost ARB implies retrying the transaction from
 396                  * the first message, after the "winning" master issues
 397                  * its STOP.  As a rule, upper layer code has no reason
 398                  * to know or care about this ... it is *NOT* an error.
 399                  */
 400                 } else {
 401                         dev_err(&i2c_adap->dev, "sendbytes: error %d\n",
 402                                         retval);
 403                         return retval;
 404                 }
 405         }
 406         return wrcount;
 407 }
 408
 409 static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
 410 {
 411         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 412
 413         /* assert: sda is high */
 414         if (is_ack)             /* send ack */
 415                 setsda(adap, 0);
 416         udelay((adap->udelay + 1) / 2);
 417         if (sclhi(adap) < 0) {  /* timeout */
 418                 dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
 419                 return -ETIMEDOUT;
 420         }
 421         scllo(adap);
 422         return 0;
 423 }
 424
 425 static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 426 {
 427         int inval;
 428         int rdcount = 0;        /* counts bytes read */
 429         unsigned char *temp = msg->buf;
 430         int count = msg->len;
 431         const unsigned flags = msg->flags;
 432
 433         while (count > 0) {
 434                 inval = i2c_inb(i2c_adap);
 435                 if (inval >= 0) {
 436                         *temp = inval;
 437                         rdcount++;
 438                 } else {   /* read timed out */
 439                         break;
 440                 }
 441
 442                 temp++;
 443                 count--;
 444
 445                 /* Some SMBus transactions require that we receive the
 446                    transaction length as the first read byte. */
 447                 if (rdcount == 1 && (flags & I2C_M_RECV_LEN)) {
 448                         if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
 449                                 if (!(flags & I2C_M_NO_RD_ACK))
 450                                         acknak(i2c_adap, 0);
 451                                 dev_err(&i2c_adap->dev,
 452                                         "readbytes: invalid block length (%d)\n",
 453                                         inval);
 454                                 return -EPROTO;
 455                         }
 456                         /* The original count value accounts for the extra
 457                            bytes, that is, either 1 for a regular transaction,
 458                            or 2 for a PEC transaction. */
 459                         count += inval;
 460                         msg->len += inval;
 461                 }
 462
 463                 bit_dbg(2, &i2c_adap->dev, "readbytes: 0x%02x %s\n",
 464                         inval,
 465                         (flags & I2C_M_NO_RD_ACK)
 466                                 ? "(no ack/nak)"
 467                                 : (count ? "A" : "NA"));
 468
 469                 if (!(flags & I2C_M_NO_RD_ACK)) {
 470                         inval = acknak(i2c_adap, count);
 471                         if (inval < 0)
 472                                 return inval;
 473                 }
 474         }
 475         return rdcount;
 476 }
 477
 478 /* doAddress initiates the transfer by generating the start condition (in
 479  * try_address) and transmits the address in the necessary format to handle
 480  * reads, writes as well as 10bit-addresses.
 481  * returns:
 482  *  0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
 483  * -x an error occurred (like: -ENXIO if the device did not answer, or
 484  *      -ETIMEDOUT, for example if the lines are stuck...)
 485  */
 486 static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 487 {
 488         unsigned short flags = msg->flags;
 489         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 490         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 491
 492         unsigned char addr;
 493         int ret, retries;
 494
 495         retries = nak_ok ? 0 : i2c_adap->retries;
 496
 497         if (flags & I2C_M_TEN) {
 498                 /* a ten bit address */
 499                 addr = 0xf0 | ((msg->addr >> 7) & 0x06);
 500                 bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
 501                 /* try extended address code...*/
 502                 ret = try_address(i2c_adap, addr, retries);
 503                 if ((ret != 1) && !nak_ok)  {
 504                         dev_err(&i2c_adap->dev,
 505                                 "died at extended address code\n");
 506                         return -ENXIO;
 507                 }
 508                 /* the remaining 8 bit address */
 509                 ret = i2c_outb(i2c_adap, msg->addr & 0xff);
 510                 if ((ret != 1) && !nak_ok) {
 511                         /* the chip did not ack / xmission error occurred */
 512                         dev_err(&i2c_adap->dev, "died at 2nd address code\n");
 513                         return -ENXIO;
 514                 }
 515                 if (flags & I2C_M_RD) {
 516                         bit_dbg(3, &i2c_adap->dev,
 517                                 "emitting repeated start condition\n");
 518                         i2c_repstart(adap);
 519                         /* okay, now switch into reading mode */
 520                         addr |= 0x01;
 521                         ret = try_address(i2c_adap, addr, retries);
 522                         if ((ret != 1) && !nak_ok) {
 523                                 dev_err(&i2c_adap->dev,
 524                                         "died at repeated address code\n");
 525                                 return -EIO;
 526                         }
 527                 }
 528         } else {                /* normal 7bit address  */
 529                 addr = i2c_8bit_addr_from_msg(msg);
 530                 if (flags & I2C_M_REV_DIR_ADDR)
 531                         addr ^= 1;
 532                 ret = try_address(i2c_adap, addr, retries);
 533                 if ((ret != 1) && !nak_ok)
 534                         return -ENXIO;
 535         }
 536
 537         return 0;
 538 }
 539
 540 static int bit_xfer(struct i2c_adapter *i2c_adap,
 541                     struct i2c_msg msgs[], int num)
 542 {
 543         struct i2c_msg *pmsg;
 544         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 545         int i, ret;
 546         unsigned short nak_ok;
 547
 548         if (adap->pre_xfer) {
 549                 ret = adap->pre_xfer(i2c_adap);
 550                 if (ret < 0)
 551                         return ret;
 552         }
 553
 554         bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 555         i2c_start(adap);
 556         for (i = 0; i < num; i++) {
 557                 pmsg = &msgs[i];
 558                 nak_ok = pmsg->flags & I2C_M_IGNORE_NAK;
 559                 if (!(pmsg->flags & I2C_M_NOSTART)) {
 560                         if (i) {
 561                                 if (msgs[i - 1].flags & I2C_M_STOP) {
 562                                         bit_dbg(3, &i2c_adap->dev,
 563                                                 "emitting enforced stop/start condition\n");
 564                                         i2c_stop(adap);
 565                                         i2c_start(adap);
 566                                 } else {
 567                                         bit_dbg(3, &i2c_adap->dev,
 568                                                 "emitting repeated start condition\n");
 569                                         i2c_repstart(adap);
 570                                 }
 571                         }
 572                         ret = bit_doAddress(i2c_adap, pmsg);
 573                         if ((ret != 0) && !nak_ok) {
 574                                 bit_dbg(1, &i2c_adap->dev,
 575                                         "NAK from device addr 0x%02x msg #%d\n",
 576                                         msgs[i].addr, i);
 577                                 goto bailout;
 578                         }
 579                 }
 580                 if (pmsg->flags & I2C_M_RD) {
 581                         /* read bytes into buffer*/
 582                         ret = readbytes(i2c_adap, pmsg);
 583                         if (ret >= 1)
 584                                 bit_dbg(2, &i2c_adap->dev, "read %d byte%s\n",
 585                                         ret, ret == 1 ? "" : "s");
 586                         if (ret < pmsg->len) {
 587                                 if (ret >= 0)
 588                                         ret = -EIO;
 589                                 goto bailout;
 590                         }
 591                 } else {
 592                         /* write bytes from buffer */
 593                         ret = sendbytes(i2c_adap, pmsg);
 594                         if (ret >= 1)
 595                                 bit_dbg(2, &i2c_adap->dev, "wrote %d byte%s\n",
 596                                         ret, ret == 1 ? "" : "s");
 597                         if (ret < pmsg->len) {
 598                                 if (ret >= 0)
 599                                         ret = -EIO;
 600                                 goto bailout;
 601                         }
 602                 }
 603         }
 604         ret = i;
 605
 606 bailout:
 607         bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 608         i2c_stop(adap);
 609
 610         if (adap->post_xfer)
 611                 adap->post_xfer(i2c_adap);
 612         return ret;
 613 }
 614
 615 static u32 bit_func(struct i2c_adapter *adap)
 616 {
 617         return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
 618                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 619                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 620                I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
 621 }
 622
 623
 624 /* -----exported algorithm data: -------------------------------------  */
 625
 626 const struct i2c_algorithm i2c_bit_algo = {
 627         .master_xfer    = bit_xfer,
 628         .functionality  = bit_func,
 629 };
 630 EXPORT_SYMBOL(i2c_bit_algo);
 631
 632 static const struct i2c_adapter_quirks i2c_bit_quirk_no_clk_stretch = {
 633         .flags = I2C_AQ_NO_CLK_STRETCH,
 634 };
 635
 636 /*
 637  * registering functions to load algorithms at runtime
 638  */
 639 static int __i2c_bit_add_bus(struct i2c_adapter *adap,
 640                              int (*add_adapter)(struct i2c_adapter *))
 641 {
 642         struct i2c_algo_bit_data *bit_adap = adap->algo_data;
 643         int ret;
 644
 645         if (bit_test) {
 646                 ret = test_bus(adap);
 647                 if (bit_test >= 2 && ret < 0)
 648                         return -ENODEV;
 649         }
 650
 651         /* register new adapter to i2c module... */
 652         adap->algo = &i2c_bit_algo;
 653         adap->retries = 3;
 654         if (bit_adap->getscl == NULL)
 655                 adap->quirks = &i2c_bit_quirk_no_clk_stretch;
 656
 657         /*
 658          * We tried forcing SCL/SDA to an initial state here. But that caused a
 659          * regression, sadly. Check Bugzilla #200045 for details.
 660          */
 661
 662         ret = add_adapter(adap);
 663         if (ret < 0)
 664                 return ret;
 665
 666         /* Complain if SCL can't be read */
 667         if (bit_adap->getscl == NULL) {
 668                 dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
 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 <[email protected]>");
 687 MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
 688 MODULE_LICENSE("GPL");