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
35static int bit_test; /* see if the line-setting functions work */
36module_param(bit_test, int, S_IRUGO);
37MODULE_PARM_DESC(bit_test, "lines testing - 0 off; 1 report; 2 fail if stuck");
38
39#ifdef DEBUG
40static int i2c_debug = 1;
41module_param(i2c_debug, int, S_IRUGO | S_IWUSR);
42MODULE_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
53static inline void sdalo(struct i2c_algo_bit_data *adap)
54{
55 setsda(adap, 0);
56 udelay(usec: (adap->udelay + 1) / 2);
57}
58
59static inline void sdahi(struct i2c_algo_bit_data *adap)
60{
61 setsda(adap, 1);
62 udelay(usec: (adap->udelay + 1) / 2);
63}
64
65static inline void scllo(struct i2c_algo_bit_data *adap)
66{
67 setscl(adap, 0);
68 udelay(usec: adap->udelay / 2);
69}
70
71/*
72 * Raise scl line, and do checking for delays. This is necessary for slower
73 * devices.
74 */
75static 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
108done:
109 udelay(usec: adap->udelay);
110 return 0;
111}
112
113
114/* --- other auxiliary functions -------------------------------------- */
115static void i2c_start(struct i2c_algo_bit_data *adap)
116{
117 /* assert: scl, sda are high */
118 setsda(adap, 0);
119 udelay(usec: adap->udelay);
120 scllo(adap);
121}
122
123static 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(usec: adap->udelay);
130 scllo(adap);
131}
132
133
134static 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(usec: 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 */
152static 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(usec: (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
199static 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(usec: 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 */
230static 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;
299bailout:
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 */
319static 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, c: 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(usec: 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
344static 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, c: *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
385static 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(usec: (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
401static 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, is_ack: 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, is_ack: 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 */
466static 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, c: 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
520static 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, msg: 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, msg: 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, msg: 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
586bailout:
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 */
601static 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
612static 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
621const struct i2c_algorithm i2c_bit_algo = {
622 .xfer = bit_xfer,
623 .xfer_atomic = bit_xfer_atomic,
624 .functionality = bit_func,
625};
626EXPORT_SYMBOL(i2c_bit_algo);
627
628static 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 */
635static 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(i2c_adap: 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
674int i2c_bit_add_bus(struct i2c_adapter *adap)
675{
676 return __i2c_bit_add_bus(adap, add_adapter: i2c_add_adapter);
677}
678EXPORT_SYMBOL(i2c_bit_add_bus);
679
680int i2c_bit_add_numbered_bus(struct i2c_adapter *adap)
681{
682 return __i2c_bit_add_bus(adap, add_adapter: i2c_add_numbered_adapter);
683}
684EXPORT_SYMBOL(i2c_bit_add_numbered_bus);
685
686MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
687MODULE_DESCRIPTION("I2C-Bus bit-banging algorithm");
688MODULE_LICENSE("GPL");
689