summaryrefslogtreecommitdiff
path: root/drivers/i2c/chips/at24.c
blob: d4775528abc69b2d4c4d580d712e48862ef7d1d7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
/*
 * at24.c - handle most I2C EEPROMs
 *
 * Copyright (C) 2005-2007 David Brownell
 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/mutex.h>
#include <linux/sysfs.h>
#include <linux/mod_devicetable.h>
#include <linux/log2.h>
#include <linux/bitops.h>
#include <linux/jiffies.h>
#include <linux/i2c.h>
#include <linux/i2c/at24.h>

/*
 * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
 * Differences between different vendor product lines (like Atmel AT24C or
 * MicroChip 24LC, etc) won't much matter for typical read/write access.
 * There are also I2C RAM chips, likewise interchangeable. One example
 * would be the PCF8570, which acts like a 24c02 EEPROM (256 bytes).
 *
 * However, misconfiguration can lose data. "Set 16-bit memory address"
 * to a part with 8-bit addressing will overwrite data. Writing with too
 * big a page size also loses data. And it's not safe to assume that the
 * conventional addresses 0x50..0x57 only hold eeproms; a PCF8563 RTC
 * uses 0x51, for just one example.
 *
 * Accordingly, explicit board-specific configuration data should be used
 * in almost all cases. (One partial exception is an SMBus used to access
 * "SPD" data for DRAM sticks. Those only use 24c02 EEPROMs.)
 *
 * So this driver uses "new style" I2C driver binding, expecting to be
 * told what devices exist. That may be in arch/X/mach-Y/board-Z.c or
 * similar kernel-resident tables; or, configuration data coming from
 * a bootloader.
 *
 * Other than binding model, current differences from "eeprom" driver are
 * that this one handles write access and isn't restricted to 24c02 devices.
 * It also handles larger devices (32 kbit and up) with two-byte addresses,
 * which won't work on pure SMBus systems.
 */

struct at24_data {
	struct at24_platform_data chip;
	bool use_smbus;

	/*
	 * Lock protects against activities from other Linux tasks,
	 * but not from changes by other I2C masters.
	 */
	struct mutex lock;
	struct bin_attribute bin;

	u8 *writebuf;
	unsigned write_max;
	unsigned num_addresses;

	/*
	 * Some chips tie up multiple I2C addresses; dummy devices reserve
	 * them for us, and we'll use them with SMBus calls.
	 */
	struct i2c_client *client[];
};

/*
 * This parameter is to help this driver avoid blocking other drivers out
 * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
 * clock, one 256 byte read takes about 1/43 second which is excessive;
 * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
 * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
 *
 * This value is forced to be a power of two so that writes align on pages.
 */
static unsigned io_limit = 128;
module_param(io_limit, uint, 0);
MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");

/*
 * Specs often allow 5 msec for a page write, sometimes 20 msec;
 * it's important to recover from write timeouts.
 */
static unsigned write_timeout = 25;
module_param(write_timeout, uint, 0);
MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");

#define AT24_SIZE_BYTELEN 5
#define AT24_SIZE_FLAGS 8

#define AT24_BITMASK(x) (BIT(x) - 1)

/* create non-zero magic value for given eeprom parameters */
#define AT24_DEVICE_MAGIC(_len, _flags) 		\
	((1 << AT24_SIZE_FLAGS | (_flags)) 		\
	    << AT24_SIZE_BYTELEN | ilog2(_len))

static const struct i2c_device_id at24_ids[] = {
	/* needs 8 addresses as A0-A2 are ignored */
	{ "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },
	/* old variants can't be handled with this generic entry! */
	{ "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
	{ "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
	/* spd is a 24c02 in memory DIMMs */
	{ "spd", AT24_DEVICE_MAGIC(2048 / 8,
		AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
	{ "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },
	/* 24rf08 quirk is handled at i2c-core */
	{ "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },
	{ "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },
	{ "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },
	{ "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },
	{ "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },
	{ "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },
	{ "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },
	{ "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },
	{ "at24", 0 },
	{ /* END OF LIST */ }
};
MODULE_DEVICE_TABLE(i2c, at24_ids);

/*-------------------------------------------------------------------------*/

/*
 * This routine supports chips which consume multiple I2C addresses. It
 * computes the addressing information to be used for a given r/w request.
 * Assumes that sanity checks for offset happened at sysfs-layer.
 */
static struct i2c_client *at24_translate_offset(struct at24_data *at24,
		unsigned *offset)
{
	unsigned i;

	if (at24->chip.flags & AT24_FLAG_ADDR16) {
		i = *offset >> 16;
		*offset &= 0xffff;
	} else {
		i = *offset >> 8;
		*offset &= 0xff;
	}

	return at24->client[i];
}

static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
		unsigned offset, size_t count)
{
	struct i2c_msg msg[2];
	u8 msgbuf[2];
	struct i2c_client *client;
	int status, i;

	memset(msg, 0, sizeof(msg));

	/*
	 * REVISIT some multi-address chips don't rollover page reads to
	 * the next slave address, so we may need to truncate the count.
	 * Those chips might need another quirk flag.
	 *
	 * If the real hardware used four adjacent 24c02 chips and that
	 * were misconfigured as one 24c08, that would be a similar effect:
	 * one "eeprom" file not four, but larger reads would fail when
	 * they crossed certain pages.
	 */

	/*
	 * Slave address and byte offset derive from the offset. Always
	 * set the byte address; on a multi-master board, another master
	 * may have changed the chip's "current" address pointer.
	 */
	client = at24_translate_offset(at24, &offset);

	if (count > io_limit)
		count = io_limit;

	/* Smaller eeproms can work given some SMBus extension calls */
	if (at24->use_smbus) {
		if (count > I2C_SMBUS_BLOCK_MAX)
			count = I2C_SMBUS_BLOCK_MAX;
		status = i2c_smbus_read_i2c_block_data(client, offset,
				count, buf);
		dev_dbg(&client->dev, "smbus read %zu@%d --> %d\n",
				count, offset, status);
		return (status < 0) ? -EIO : status;
	}

	/*
	 * When we have a better choice than SMBus calls, use a combined
	 * I2C message. Write address; then read up to io_limit data bytes.
	 * Note that read page rollover helps us here (unlike writes).
	 * msgbuf is u8 and will cast to our needs.
	 */
	i = 0;
	if (at24->chip.flags & AT24_FLAG_ADDR16)
		msgbuf[i++] = offset >> 8;
	msgbuf[i++] = offset;

	msg[0].addr = client->addr;
	msg[0].buf = msgbuf;
	msg[0].len = i;

	msg[1].addr = client->addr;
	msg[1].flags = I2C_M_RD;
	msg[1].buf = buf;
	msg[1].len = count;

	status = i2c_transfer(client->adapter, msg, 2);
	dev_dbg(&client->dev, "i2c read %zu@%d --> %d\n",
			count, offset, status);

	if (status == 2)
		return count;
	else if (status >= 0)
		return -EIO;
	else
		return status;
}

static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
		char *buf, loff_t off, size_t count)
{
	struct at24_data *at24;
	ssize_t retval = 0;

	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));

	if (unlikely(!count))
		return count;

	/*
	 * Read data from chip, protecting against concurrent updates
	 * from this host, but not from other I2C masters.
	 */
	mutex_lock(&at24->lock);

	while (count) {
		ssize_t	status;

		status = at24_eeprom_read(at24, buf, off, count);
		if (status <= 0) {
			if (retval == 0)
				retval = status;
			break;
		}
		buf += status;
		off += status;
		count -= status;
		retval += status;
	}

	mutex_unlock(&at24->lock);

	return retval;
}


/*
 * REVISIT: export at24_bin{read,write}() to let other kernel code use
 * eeprom data. For example, it might hold a board's Ethernet address, or
 * board-specific calibration data generated on the manufacturing floor.
 */


/*
 * Note that if the hardware write-protect pin is pulled high, the whole
 * chip is normally write protected. But there are plenty of product
 * variants here, including OTP fuses and partial chip protect.
 *
 * We only use page mode writes; the alternative is sloooow. This routine
 * writes at most one page.
 */
static ssize_t at24_eeprom_write(struct at24_data *at24, char *buf,
		unsigned offset, size_t count)
{
	struct i2c_client *client;
	struct i2c_msg msg;
	ssize_t status;
	unsigned long timeout, write_time;
	unsigned next_page;

	/* Get corresponding I2C address and adjust offset */
	client = at24_translate_offset(at24, &offset);

	/* write_max is at most a page */
	if (count > at24->write_max)
		count = at24->write_max;

	/* Never roll over backwards, to the start of this page */
	next_page = roundup(offset + 1, at24->chip.page_size);
	if (offset + count > next_page)
		count = next_page - offset;

	/* If we'll use I2C calls for I/O, set up the message */
	if (!at24->use_smbus) {
		int i = 0;

		msg.addr = client->addr;
		msg.flags = 0;

		/* msg.buf is u8 and casts will mask the values */
		msg.buf = at24->writebuf;
		if (at24->chip.flags & AT24_FLAG_ADDR16)
			msg.buf[i++] = offset >> 8;

		msg.buf[i++] = offset;
		memcpy(&msg.buf[i], buf, count);
		msg.len = i + count;
	}

	/*
	 * Writes fail if the previous one didn't complete yet. We may
	 * loop a few times until this one succeeds, waiting at least
	 * long enough for one entire page write to work.
	 */
	timeout = jiffies + msecs_to_jiffies(write_timeout);
	do {
		write_time = jiffies;
		if (at24->use_smbus) {
			status = i2c_smbus_write_i2c_block_data(client,
					offset, count, buf);
			if (status == 0)
				status = count;
		} else {
			status = i2c_transfer(client->adapter, &msg, 1);
			if (status == 1)
				status = count;
		}
		dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
				count, offset, status, jiffies);

		if (status == count)
			return count;

		/* REVISIT: at HZ=100, this is sloooow */
		msleep(1);
	} while (time_before(write_time, timeout));

	return -ETIMEDOUT;
}

static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
		char *buf, loff_t off, size_t count)
{
	struct at24_data *at24;
	ssize_t retval = 0;

	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));

	if (unlikely(!count))
		return count;

	/*
	 * Write data to chip, protecting against concurrent updates
	 * from this host, but not from other I2C masters.
	 */
	mutex_lock(&at24->lock);

	while (count) {
		ssize_t	status;

		status = at24_eeprom_write(at24, buf, off, count);
		if (status <= 0) {
			if (retval == 0)
				retval = status;
			break;
		}
		buf += status;
		off += status;
		count -= status;
		retval += status;
	}

	mutex_unlock(&at24->lock);

	return retval;
}

/*-------------------------------------------------------------------------*/

static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
	struct at24_platform_data chip;
	bool writable;
	bool use_smbus = false;
	struct at24_data *at24;
	int err;
	unsigned i, num_addresses;
	kernel_ulong_t magic;

	if (client->dev.platform_data) {
		chip = *(struct at24_platform_data *)client->dev.platform_data;
	} else {
		if (!id->driver_data) {
			err = -ENODEV;
			goto err_out;
		}
		magic = id->driver_data;
		chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
		magic >>= AT24_SIZE_BYTELEN;
		chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
		/*
		 * This is slow, but we can't know all eeproms, so we better
		 * play safe. Specifying custom eeprom-types via platform_data
		 * is recommended anyhow.
		 */
		chip.page_size = 1;
	}

	if (!is_power_of_2(chip.byte_len))
		dev_warn(&client->dev,
			"byte_len looks suspicious (no power of 2)!\n");
	if (!is_power_of_2(chip.page_size))
		dev_warn(&client->dev,
			"page_size looks suspicious (no power of 2)!\n");

	/* Use I2C operations unless we're stuck with SMBus extensions. */
	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
		if (chip.flags & AT24_FLAG_ADDR16) {
			err = -EPFNOSUPPORT;
			goto err_out;
		}
		if (!i2c_check_functionality(client->adapter,
				I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
			err = -EPFNOSUPPORT;
			goto err_out;
		}
		use_smbus = true;
	}

	if (chip.flags & AT24_FLAG_TAKE8ADDR)
		num_addresses = 8;
	else
		num_addresses =	DIV_ROUND_UP(chip.byte_len,
			(chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);

	at24 = kzalloc(sizeof(struct at24_data) +
		num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
	if (!at24) {
		err = -ENOMEM;
		goto err_out;
	}

	mutex_init(&at24->lock);
	at24->use_smbus = use_smbus;
	at24->chip = chip;
	at24->num_addresses = num_addresses;

	/*
	 * Export the EEPROM bytes through sysfs, since that's convenient.
	 * By default, only root should see the data (maybe passwords etc)
	 */
	at24->bin.attr.name = "eeprom";
	at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
	at24->bin.read = at24_bin_read;
	at24->bin.size = chip.byte_len;

	writable = !(chip.flags & AT24_FLAG_READONLY);
	if (writable) {
		if (!use_smbus || i2c_check_functionality(client->adapter,
				I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {

			unsigned write_max = chip.page_size;

			at24->bin.write = at24_bin_write;
			at24->bin.attr.mode |= S_IWUSR;

			if (write_max > io_limit)
				write_max = io_limit;
			if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
				write_max = I2C_SMBUS_BLOCK_MAX;
			at24->write_max = write_max;

			/* buffer (data + address at the beginning) */
			at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
			if (!at24->writebuf) {
				err = -ENOMEM;
				goto err_struct;
			}
		} else {
			dev_warn(&client->dev,
				"cannot write due to controller restrictions.");
		}
	}

	at24->client[0] = client;

	/* use dummy devices for multiple-address chips */
	for (i = 1; i < num_addresses; i++) {
		at24->client[i] = i2c_new_dummy(client->adapter,
					client->addr + i);
		if (!at24->client[i]) {
			dev_err(&client->dev, "address 0x%02x unavailable\n",
					client->addr + i);
			err = -EADDRINUSE;
			goto err_clients;
		}
	}

	err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
	if (err)
		goto err_clients;

	i2c_set_clientdata(client, at24);

	dev_info(&client->dev, "%zu byte %s EEPROM %s\n",
		at24->bin.size, client->name,
		writable ? "(writable)" : "(read-only)");
	dev_dbg(&client->dev,
		"page_size %d, num_addresses %d, write_max %d%s\n",
		chip.page_size, num_addresses,
		at24->write_max,
		use_smbus ? ", use_smbus" : "");

	return 0;

err_clients:
	for (i = 1; i < num_addresses; i++)
		if (at24->client[i])
			i2c_unregister_device(at24->client[i]);

	kfree(at24->writebuf);
err_struct:
	kfree(at24);
err_out:
	dev_dbg(&client->dev, "probe error %d\n", err);
	return err;
}

static int __devexit at24_remove(struct i2c_client *client)
{
	struct at24_data *at24;
	int i;

	at24 = i2c_get_clientdata(client);
	sysfs_remove_bin_file(&client->dev.kobj, &at24->bin);

	for (i = 1; i < at24->num_addresses; i++)
		i2c_unregister_device(at24->client[i]);

	kfree(at24->writebuf);
	kfree(at24);
	i2c_set_clientdata(client, NULL);
	return 0;
}

/*-------------------------------------------------------------------------*/

static struct i2c_driver at24_driver = {
	.driver = {
		.name = "at24",
		.owner = THIS_MODULE,
	},
	.probe = at24_probe,
	.remove = __devexit_p(at24_remove),
	.id_table = at24_ids,
};

static int __init at24_init(void)
{
	io_limit = rounddown_pow_of_two(io_limit);
	return i2c_add_driver(&at24_driver);
}
module_init(at24_init);

static void __exit at24_exit(void)
{
	i2c_del_driver(&at24_driver);
}
module_exit(at24_exit);

MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
MODULE_AUTHOR("David Brownell and Wolfram Sang");
MODULE_LICENSE("GPL");