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

DEFINITIONS

1. sdalo
2. sdahi
3. scllo
4. sclhi
5. i2c_start
6. i2c_repstart
7. i2c_stop
8. i2c_outb
9. i2c_inb
10. test_bus
11. try_address
12. sendbytes
13. acknak
14. readbytes
15. bit_doAddress
16. bit_xfer
17. bit_xfer_atomic
18. bit_func
19. __i2c_bit_add_bus
20. i2c_bit_add_bus
21. i2c_bit_add_numbered_bus

   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          */
 188         ack = !getsda(adap);    /* ack: sda is pulled low -> success */
 189         bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
 190                 ack ? "A" : "NA");
 191 
 192         scllo(adap);
 193         return ack;
 194         /* assert: scl is low (sda undef) */
 195 }
 196 
 197 
 198 static int i2c_inb(struct i2c_adapter *i2c_adap)
 199 {
 200         /* read byte via i2c port, without start/stop sequence  */
 201         /* acknowledge is sent in i2c_read.                     */
 202         int i;
 203         unsigned char indata = 0;
 204         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 205 
 206         /* assert: scl is low */
 207         sdahi(adap);
 208         for (i = 0; i < 8; i++) {
 209                 if (sclhi(adap) < 0) { /* timeout */
 210                         bit_dbg(1, &i2c_adap->dev,
 211                                 "i2c_inb: timeout at bit #%d\n",
 212                                 7 - i);
 213                         return -ETIMEDOUT;
 214                 }
 215                 indata *= 2;
 216                 if (getsda(adap))
 217                         indata |= 0x01;
 218                 setscl(adap, 0);
 219                 udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
 220         }
 221         /* assert: scl is low */
 222         return indata;
 223 }
 224 
 225 /*
 226  * Sanity check for the adapter hardware - check the reaction of
 227  * the bus lines only if it seems to be idle.
 228  */
 229 static int test_bus(struct i2c_adapter *i2c_adap)
 230 {
 231         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 232         const char *name = i2c_adap->name;
 233         int scl, sda, ret;
 234 
 235         if (adap->pre_xfer) {
 236                 ret = adap->pre_xfer(i2c_adap);
 237                 if (ret < 0)
 238                         return -ENODEV;
 239         }
 240 
 241         if (adap->getscl == NULL)
 242                 pr_info("%s: Testing SDA only, SCL is not readable\n", name);
 243 
 244         sda = getsda(adap);
 245         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 246         if (!scl || !sda) {
 247                 printk(KERN_WARNING
 248                        "%s: bus seems to be busy (scl=%d, sda=%d)\n",
 249                        name, scl, sda);
 250                 goto bailout;
 251         }
 252 
 253         sdalo(adap);
 254         sda = getsda(adap);
 255         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 256         if (sda) {
 257                 printk(KERN_WARNING "%s: SDA stuck high!\n", name);
 258                 goto bailout;
 259         }
 260         if (!scl) {
 261                 printk(KERN_WARNING
 262                        "%s: SCL unexpected low while pulling SDA low!\n",
 263                        name);
 264                 goto bailout;
 265         }
 266 
 267         sdahi(adap);
 268         sda = getsda(adap);
 269         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 270         if (!sda) {
 271                 printk(KERN_WARNING "%s: SDA stuck low!\n", name);
 272                 goto bailout;
 273         }
 274         if (!scl) {
 275                 printk(KERN_WARNING
 276                        "%s: SCL unexpected low while pulling SDA high!\n",
 277                        name);
 278                 goto bailout;
 279         }
 280 
 281         scllo(adap);
 282         sda = getsda(adap);
 283         scl = (adap->getscl == NULL) ? 0 : getscl(adap);
 284         if (scl) {
 285                 printk(KERN_WARNING "%s: SCL stuck high!\n", name);
 286                 goto bailout;
 287         }
 288         if (!sda) {
 289                 printk(KERN_WARNING
 290                        "%s: SDA unexpected low while pulling SCL low!\n",
 291                        name);
 292                 goto bailout;
 293         }
 294 
 295         sclhi(adap);
 296         sda = getsda(adap);
 297         scl = (adap->getscl == NULL) ? 1 : getscl(adap);
 298         if (!scl) {
 299                 printk(KERN_WARNING "%s: SCL stuck low!\n", name);
 300                 goto bailout;
 301         }
 302         if (!sda) {
 303                 printk(KERN_WARNING
 304                        "%s: SDA unexpected low while pulling SCL high!\n",
 305                        name);
 306                 goto bailout;
 307         }
 308 
 309         if (adap->post_xfer)
 310                 adap->post_xfer(i2c_adap);
 311 
 312         pr_info("%s: Test OK\n", name);
 313         return 0;
 314 bailout:
 315         sdahi(adap);
 316         sclhi(adap);
 317 
 318         if (adap->post_xfer)
 319                 adap->post_xfer(i2c_adap);
 320 
 321         return -ENODEV;
 322 }
 323 
 324 /* ----- Utility functions
 325  */
 326 
 327 /* try_address tries to contact a chip for a number of
 328  * times before it gives up.
 329  * return values:
 330  * 1 chip answered
 331  * 0 chip did not answer
 332  * -x transmission error
 333  */
 334 static int try_address(struct i2c_adapter *i2c_adap,
 335                        unsigned char addr, int retries)
 336 {
 337         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 338         int i, ret = 0;
 339 
 340         for (i = 0; i <= retries; i++) {
 341                 ret = i2c_outb(i2c_adap, addr);
 342                 if (ret == 1 || i == retries)
 343                         break;
 344                 bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 345                 i2c_stop(adap);
 346                 udelay(adap->udelay);
 347                 yield();
 348                 bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 349                 i2c_start(adap);
 350         }
 351         if (i && ret)
 352                 bit_dbg(1, &i2c_adap->dev,
 353                         "Used %d tries to %s client at 0x%02x: %s\n", i + 1,
 354                         addr & 1 ? "read from" : "write to", addr >> 1,
 355                         ret == 1 ? "success" : "failed, timeout?");
 356         return ret;
 357 }
 358 
 359 static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 360 {
 361         const unsigned char *temp = msg->buf;
 362         int count = msg->len;
 363         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 364         int retval;
 365         int wrcount = 0;
 366 
 367         while (count > 0) {
 368                 retval = i2c_outb(i2c_adap, *temp);
 369 
 370                 /* OK/ACK; or ignored NAK */
 371                 if ((retval > 0) || (nak_ok && (retval == 0))) {
 372                         count--;
 373                         temp++;
 374                         wrcount++;
 375 
 376                 /* A slave NAKing the master means the slave didn't like
 377                  * something about the data it saw.  For example, maybe
 378                  * the SMBus PEC was wrong.
 379                  */
 380                 } else if (retval == 0) {
 381                         dev_err(&i2c_adap->dev, "sendbytes: NAK bailout.\n");
 382                         return -EIO;
 383 
 384                 /* Timeout; or (someday) lost arbitration
 385                  *
 386                  * FIXME Lost ARB implies retrying the transaction from
 387                  * the first message, after the "winning" master issues
 388                  * its STOP.  As a rule, upper layer code has no reason
 389                  * to know or care about this ... it is *NOT* an error.
 390                  */
 391                 } else {
 392                         dev_err(&i2c_adap->dev, "sendbytes: error %d\n",
 393                                         retval);
 394                         return retval;
 395                 }
 396         }
 397         return wrcount;
 398 }
 399 
 400 static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
 401 {
 402         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 403 
 404         /* assert: sda is high */
 405         if (is_ack)             /* send ack */
 406                 setsda(adap, 0);
 407         udelay((adap->udelay + 1) / 2);
 408         if (sclhi(adap) < 0) {  /* timeout */
 409                 dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
 410                 return -ETIMEDOUT;
 411         }
 412         scllo(adap);
 413         return 0;
 414 }
 415 
 416 static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 417 {
 418         int inval;
 419         int rdcount = 0;        /* counts bytes read */
 420         unsigned char *temp = msg->buf;
 421         int count = msg->len;
 422         const unsigned flags = msg->flags;
 423 
 424         while (count > 0) {
 425                 inval = i2c_inb(i2c_adap);
 426                 if (inval >= 0) {
 427                         *temp = inval;
 428                         rdcount++;
 429                 } else {   /* read timed out */
 430                         break;
 431                 }
 432 
 433                 temp++;
 434                 count--;
 435 
 436                 /* Some SMBus transactions require that we receive the
 437                    transaction length as the first read byte. */
 438                 if (rdcount == 1 && (flags & I2C_M_RECV_LEN)) {
 439                         if (inval <= 0 || inval > I2C_SMBUS_BLOCK_MAX) {
 440                                 if (!(flags & I2C_M_NO_RD_ACK))
 441                                         acknak(i2c_adap, 0);
 442                                 dev_err(&i2c_adap->dev,
 443                                         "readbytes: invalid block length (%d)\n",
 444                                         inval);
 445                                 return -EPROTO;
 446                         }
 447                         /* The original count value accounts for the extra
 448                            bytes, that is, either 1 for a regular transaction,
 449                            or 2 for a PEC transaction. */
 450                         count += inval;
 451                         msg->len += inval;
 452                 }
 453 
 454                 bit_dbg(2, &i2c_adap->dev, "readbytes: 0x%02x %s\n",
 455                         inval,
 456                         (flags & I2C_M_NO_RD_ACK)
 457                                 ? "(no ack/nak)"
 458                                 : (count ? "A" : "NA"));
 459 
 460                 if (!(flags & I2C_M_NO_RD_ACK)) {
 461                         inval = acknak(i2c_adap, count);
 462                         if (inval < 0)
 463                                 return inval;
 464                 }
 465         }
 466         return rdcount;
 467 }
 468 
 469 /* doAddress initiates the transfer by generating the start condition (in
 470  * try_address) and transmits the address in the necessary format to handle
 471  * reads, writes as well as 10bit-addresses.
 472  * returns:
 473  *  0 everything went okay, the chip ack'ed, or IGNORE_NAK flag was set
 474  * -x an error occurred (like: -ENXIO if the device did not answer, or
 475  *      -ETIMEDOUT, for example if the lines are stuck...)
 476  */
 477 static int bit_doAddress(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
 478 {
 479         unsigned short flags = msg->flags;
 480         unsigned short nak_ok = msg->flags & I2C_M_IGNORE_NAK;
 481         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 482 
 483         unsigned char addr;
 484         int ret, retries;
 485 
 486         retries = nak_ok ? 0 : i2c_adap->retries;
 487 
 488         if (flags & I2C_M_TEN) {
 489                 /* a ten bit address */
 490                 addr = 0xf0 | ((msg->addr >> 7) & 0x06);
 491                 bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
 492                 /* try extended address code...*/
 493                 ret = try_address(i2c_adap, addr, retries);
 494                 if ((ret != 1) && !nak_ok)  {
 495                         dev_err(&i2c_adap->dev,
 496                                 "died at extended address code\n");
 497                         return -ENXIO;
 498                 }
 499                 /* the remaining 8 bit address */
 500                 ret = i2c_outb(i2c_adap, msg->addr & 0xff);
 501                 if ((ret != 1) && !nak_ok) {
 502                         /* the chip did not ack / xmission error occurred */
 503                         dev_err(&i2c_adap->dev, "died at 2nd address code\n");
 504                         return -ENXIO;
 505                 }
 506                 if (flags & I2C_M_RD) {
 507                         bit_dbg(3, &i2c_adap->dev,
 508                                 "emitting repeated start condition\n");
 509                         i2c_repstart(adap);
 510                         /* okay, now switch into reading mode */
 511                         addr |= 0x01;
 512                         ret = try_address(i2c_adap, addr, retries);
 513                         if ((ret != 1) && !nak_ok) {
 514                                 dev_err(&i2c_adap->dev,
 515                                         "died at repeated address code\n");
 516                                 return -EIO;
 517                         }
 518                 }
 519         } else {                /* normal 7bit address  */
 520                 addr = i2c_8bit_addr_from_msg(msg);
 521                 if (flags & I2C_M_REV_DIR_ADDR)
 522                         addr ^= 1;
 523                 ret = try_address(i2c_adap, addr, retries);
 524                 if ((ret != 1) && !nak_ok)
 525                         return -ENXIO;
 526         }
 527 
 528         return 0;
 529 }
 530 
 531 static int bit_xfer(struct i2c_adapter *i2c_adap,
 532                     struct i2c_msg msgs[], int num)
 533 {
 534         struct i2c_msg *pmsg;
 535         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 536         int i, ret;
 537         unsigned short nak_ok;
 538 
 539         if (adap->pre_xfer) {
 540                 ret = adap->pre_xfer(i2c_adap);
 541                 if (ret < 0)
 542                         return ret;
 543         }
 544 
 545         bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
 546         i2c_start(adap);
 547         for (i = 0; i < num; i++) {
 548                 pmsg = &msgs[i];
 549                 nak_ok = pmsg->flags & I2C_M_IGNORE_NAK;
 550                 if (!(pmsg->flags & I2C_M_NOSTART)) {
 551                         if (i) {
 552                                 if (msgs[i - 1].flags & I2C_M_STOP) {
 553                                         bit_dbg(3, &i2c_adap->dev,
 554                                                 "emitting enforced stop/start condition\n");
 555                                         i2c_stop(adap);
 556                                         i2c_start(adap);
 557                                 } else {
 558                                         bit_dbg(3, &i2c_adap->dev,
 559                                                 "emitting repeated start condition\n");
 560                                         i2c_repstart(adap);
 561                                 }
 562                         }
 563                         ret = bit_doAddress(i2c_adap, pmsg);
 564                         if ((ret != 0) && !nak_ok) {
 565                                 bit_dbg(1, &i2c_adap->dev,
 566                                         "NAK from device addr 0x%02x msg #%d\n",
 567                                         msgs[i].addr, i);
 568                                 goto bailout;
 569                         }
 570                 }
 571                 if (pmsg->flags & I2C_M_RD) {
 572                         /* read bytes into buffer*/
 573                         ret = readbytes(i2c_adap, pmsg);
 574                         if (ret >= 1)
 575                                 bit_dbg(2, &i2c_adap->dev, "read %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                 } else {
 583                         /* write bytes from buffer */
 584                         ret = sendbytes(i2c_adap, pmsg);
 585                         if (ret >= 1)
 586                                 bit_dbg(2, &i2c_adap->dev, "wrote %d byte%s\n",
 587                                         ret, ret == 1 ? "" : "s");
 588                         if (ret < pmsg->len) {
 589                                 if (ret >= 0)
 590                                         ret = -EIO;
 591                                 goto bailout;
 592                         }
 593                 }
 594         }
 595         ret = i;
 596 
 597 bailout:
 598         bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
 599         i2c_stop(adap);
 600 
 601         if (adap->post_xfer)
 602                 adap->post_xfer(i2c_adap);
 603         return ret;
 604 }
 605 
 606 /*
 607  * We print a warning when we are not flagged to support atomic transfers but
 608  * will try anyhow. That's what the I2C core would do as well. Sadly, we can't
 609  * modify the algorithm struct at probe time because this struct is exported
 610  * 'const'.
 611  */
 612 static int bit_xfer_atomic(struct i2c_adapter *i2c_adap, struct i2c_msg msgs[],
 613                            int num)
 614 {
 615         struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 616 
 617         if (!adap->can_do_atomic)
 618                 dev_warn(&i2c_adap->dev, "not flagged for atomic transfers\n");
 619 
 620         return bit_xfer(i2c_adap, msgs, num);
 621 }
 622 
 623 static u32 bit_func(struct i2c_adapter *adap)
 624 {
 625         return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL |
 626                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
 627                I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
 628                I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
 629 }
 630 
 631 
 632 /* -----exported algorithm data: -------------------------------------  */
 633 
 634 const struct i2c_algorithm i2c_bit_algo = {
 635         .master_xfer = bit_xfer,
 636         .master_xfer_atomic = bit_xfer_atomic,
 637         .functionality = bit_func,
 638 };
 639 EXPORT_SYMBOL(i2c_bit_algo);
 640 
 641 static const struct i2c_adapter_quirks i2c_bit_quirk_no_clk_stretch = {
 642         .flags = I2C_AQ_NO_CLK_STRETCH,
 643 };
 644 
 645 /*
 646  * registering functions to load algorithms at runtime
 647  */
 648 static int __i2c_bit_add_bus(struct i2c_adapter *adap,
 649                              int (*add_adapter)(struct i2c_adapter *))
 650 {
 651         struct i2c_algo_bit_data *bit_adap = adap->algo_data;
 652         int ret;
 653 
 654         if (bit_test) {
 655                 ret = test_bus(adap);
 656                 if (bit_test >= 2 && ret < 0)
 657                         return -ENODEV;
 658         }
 659 
 660         /* register new adapter to i2c module... */
 661         adap->algo = &i2c_bit_algo;
 662         adap->retries = 3;
 663         if (bit_adap->getscl == NULL)
 664                 adap->quirks = &i2c_bit_quirk_no_clk_stretch;
 665 
 666         /*
 667          * We tried forcing SCL/SDA to an initial state here. But that caused a
 668          * regression, sadly. Check Bugzilla #200045 for details.
 669          */
 670 
 671         ret = add_adapter(adap);
 672         if (ret < 0)
 673                 return ret;
 674 
 675         /* Complain if SCL can't be read */
 676         if (bit_adap->getscl == NULL) {
 677                 dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");
 678                 dev_warn(&adap->dev, "Bus may be unreliable\n");
 679         }
 680         return 0;
 681 }
 682 
 683 int i2c_bit_add_bus(struct i2c_adapter *adap)
 684 {
 685         return __i2c_bit_add_bus(adap, i2c_add_adapter);
 686 }
 687 EXPORT_SYMBOL(i2c_bit_add_bus);
 688 
 689 int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
 690 {
 691         return __i2c_bit_add_bus(adap, i2c_add_numbered_adapter);
 692 }
 693 EXPORT_SYMBOL(i2c_bit_add_numbered_bus);
 694 
 695 MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
 696 MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
 697 MODULE_LICENSE("GPL");