aboutsummaryrefslogtreecommitdiff
path: root/drivers/hwmon/sht15.c
blob: bfe326e896dfd6d277ed22aec18ff9431ae8b8c1 (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
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
/*
 * sht15.c - support for the SHT15 Temperature and Humidity Sensor
 *
 * Portions Copyright (c) 2010-2012 Savoir-faire Linux Inc.
 *          Jerome Oufella <jerome.oufella@savoirfairelinux.com>
 *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>
 *
 * Copyright (c) 2009 Jonathan Cameron
 *
 * Copyright (c) 2007 Wouter Horre
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * For further information, see the Documentation/hwmon/sht15 file.
 */

#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/gpio.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/mutex.h>
#include <linux/platform_data/sht15.h>
#include <linux/platform_device.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/err.h>
#include <linux/regulator/consumer.h>
#include <linux/slab.h>
#include <linux/atomic.h>

/* Commands */
#define SHT15_MEASURE_TEMP		0x03
#define SHT15_MEASURE_RH		0x05
#define SHT15_WRITE_STATUS		0x06
#define SHT15_READ_STATUS		0x07
#define SHT15_SOFT_RESET		0x1E

/* Min timings */
#define SHT15_TSCKL			100	/* (nsecs) clock low */
#define SHT15_TSCKH			100	/* (nsecs) clock high */
#define SHT15_TSU			150	/* (nsecs) data setup time */
#define SHT15_TSRST			11	/* (msecs) soft reset time */

/* Status Register Bits */
#define SHT15_STATUS_LOW_RESOLUTION	0x01
#define SHT15_STATUS_NO_OTP_RELOAD	0x02
#define SHT15_STATUS_HEATER		0x04
#define SHT15_STATUS_LOW_BATTERY	0x40

/* List of supported chips */
enum sht15_chips { sht10, sht11, sht15, sht71, sht75 };

/* Actions the driver may be doing */
enum sht15_state {
	SHT15_READING_NOTHING,
	SHT15_READING_TEMP,
	SHT15_READING_HUMID
};

/**
 * struct sht15_temppair - elements of voltage dependent temp calc
 * @vdd:	supply voltage in microvolts
 * @d1:		see data sheet
 */
struct sht15_temppair {
	int vdd; /* microvolts */
	int d1;
};

/* Table 9 from datasheet - relates temperature calculation to supply voltage */
static const struct sht15_temppair temppoints[] = {
	{ 2500000, -39400 },
	{ 3000000, -39600 },
	{ 3500000, -39700 },
	{ 4000000, -39800 },
	{ 5000000, -40100 },
};

/* Table from CRC datasheet, section 2.4 */
static const u8 sht15_crc8_table[] = {
	0,	49,	98,	83,	196,	245,	166,	151,
	185,	136,	219,	234,	125,	76,	31,	46,
	67,	114,	33,	16,	135,	182,	229,	212,
	250,	203,	152,	169,	62,	15,	92,	109,
	134,	183,	228,	213,	66,	115,	32,	17,
	63,	14,	93,	108,	251,	202,	153,	168,
	197,	244,	167,	150,	1,	48,	99,	82,
	124,	77,	30,	47,	184,	137,	218,	235,
	61,	12,	95,	110,	249,	200,	155,	170,
	132,	181,	230,	215,	64,	113,	34,	19,
	126,	79,	28,	45,	186,	139,	216,	233,
	199,	246,	165,	148,	3,	50,	97,	80,
	187,	138,	217,	232,	127,	78,	29,	44,
	2,	51,	96,	81,	198,	247,	164,	149,
	248,	201,	154,	171,	60,	13,	94,	111,
	65,	112,	35,	18,	133,	180,	231,	214,
	122,	75,	24,	41,	190,	143,	220,	237,
	195,	242,	161,	144,	7,	54,	101,	84,
	57,	8,	91,	106,	253,	204,	159,	174,
	128,	177,	226,	211,	68,	117,	38,	23,
	252,	205,	158,	175,	56,	9,	90,	107,
	69,	116,	39,	22,	129,	176,	227,	210,
	191,	142,	221,	236,	123,	74,	25,	40,
	6,	55,	100,	85,	194,	243,	160,	145,
	71,	118,	37,	20,	131,	178,	225,	208,
	254,	207,	156,	173,	58,	11,	88,	105,
	4,	53,	102,	87,	192,	241,	162,	147,
	189,	140,	223,	238,	121,	72,	27,	42,
	193,	240,	163,	146,	5,	52,	103,	86,
	120,	73,	26,	43,	188,	141,	222,	239,
	130,	179,	224,	209,	70,	119,	36,	21,
	59,	10,	89,	104,	255,	206,	157,	172
};

/**
 * struct sht15_data - device instance specific data
 * @pdata:		platform data (gpio's etc).
 * @read_work:		bh of interrupt handler.
 * @wait_queue:		wait queue for getting values from device.
 * @val_temp:		last temperature value read from device.
 * @val_humid:		last humidity value read from device.
 * @val_status:		last status register value read from device.
 * @checksum_ok:	last value read from the device passed CRC validation.
 * @checksumming:	flag used to enable the data validation with CRC.
 * @state:		state identifying the action the driver is doing.
 * @measurements_valid:	are the current stored measures valid (start condition).
 * @status_valid:	is the current stored status valid (start condition).
 * @last_measurement:	time of last measure.
 * @last_status:	time of last status reading.
 * @read_lock:		mutex to ensure only one read in progress at a time.
 * @dev:		associate device structure.
 * @hwmon_dev:		device associated with hwmon subsystem.
 * @reg:		associated regulator (if specified).
 * @nb:			notifier block to handle notifications of voltage
 *                      changes.
 * @supply_uv:		local copy of supply voltage used to allow use of
 *                      regulator consumer if available.
 * @supply_uv_valid:	indicates that an updated value has not yet been
 *			obtained from the regulator and so any calculations
 *			based upon it will be invalid.
 * @update_supply_work:	work struct that is used to update the supply_uv.
 * @interrupt_handled:	flag used to indicate a handler has been scheduled.
 */
struct sht15_data {
	struct sht15_platform_data	*pdata;
	struct work_struct		read_work;
	wait_queue_head_t		wait_queue;
	uint16_t			val_temp;
	uint16_t			val_humid;
	u8				val_status;
	bool				checksum_ok;
	bool				checksumming;
	enum sht15_state		state;
	bool				measurements_valid;
	bool				status_valid;
	unsigned long			last_measurement;
	unsigned long			last_status;
	struct mutex			read_lock;
	struct device			*dev;
	struct device			*hwmon_dev;
	struct regulator		*reg;
	struct notifier_block		nb;
	int				supply_uv;
	bool				supply_uv_valid;
	struct work_struct		update_supply_work;
	atomic_t			interrupt_handled;
};

/**
 * sht15_reverse() - reverse a byte
 * @byte:    byte to reverse.
 */
static u8 sht15_reverse(u8 byte)
{
	u8 i, c;

	for (c = 0, i = 0; i < 8; i++)
		c |= (!!(byte & (1 << i))) << (7 - i);
	return c;
}

/**
 * sht15_crc8() - compute crc8
 * @data:	sht15 specific data.
 * @value:	sht15 retrieved data.
 *
 * This implements section 2 of the CRC datasheet.
 */
static u8 sht15_crc8(struct sht15_data *data,
		const u8 *value,
		int len)
{
	u8 crc = sht15_reverse(data->val_status & 0x0F);

	while (len--) {
		crc = sht15_crc8_table[*value ^ crc];
		value++;
	}

	return crc;
}

/**
 * sht15_connection_reset() - reset the comms interface
 * @data:	sht15 specific data
 *
 * This implements section 3.4 of the data sheet
 */
static int sht15_connection_reset(struct sht15_data *data)
{
	int i, err;

	err = gpio_direction_output(data->pdata->gpio_data, 1);
	if (err)
		return err;
	ndelay(SHT15_TSCKL);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	for (i = 0; i < 9; ++i) {
		gpio_set_value(data->pdata->gpio_sck, 1);
		ndelay(SHT15_TSCKH);
		gpio_set_value(data->pdata->gpio_sck, 0);
		ndelay(SHT15_TSCKL);
	}
	return 0;
}

/**
 * sht15_send_bit() - send an individual bit to the device
 * @data:	device state data
 * @val:	value of bit to be sent
 */
static inline void sht15_send_bit(struct sht15_data *data, int val)
{
	gpio_set_value(data->pdata->gpio_data, val);
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSCKH);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL); /* clock low time */
}

/**
 * sht15_transmission_start() - specific sequence for new transmission
 * @data:	device state data
 *
 * Timings for this are not documented on the data sheet, so very
 * conservative ones used in implementation. This implements
 * figure 12 on the data sheet.
 */
static int sht15_transmission_start(struct sht15_data *data)
{
	int err;

	/* ensure data is high and output */
	err = gpio_direction_output(data->pdata->gpio_data, 1);
	if (err)
		return err;
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSCKH);
	gpio_set_value(data->pdata->gpio_data, 0);
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSCKH);
	gpio_set_value(data->pdata->gpio_data, 1);
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	return 0;
}

/**
 * sht15_send_byte() - send a single byte to the device
 * @data:	device state
 * @byte:	value to be sent
 */
static void sht15_send_byte(struct sht15_data *data, u8 byte)
{
	int i;

	for (i = 0; i < 8; i++) {
		sht15_send_bit(data, !!(byte & 0x80));
		byte <<= 1;
	}
}

/**
 * sht15_wait_for_response() - checks for ack from device
 * @data:	device state
 */
static int sht15_wait_for_response(struct sht15_data *data)
{
	int err;

	err = gpio_direction_input(data->pdata->gpio_data);
	if (err)
		return err;
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSCKH);
	if (gpio_get_value(data->pdata->gpio_data)) {
		gpio_set_value(data->pdata->gpio_sck, 0);
		dev_err(data->dev, "Command not acknowledged\n");
		err = sht15_connection_reset(data);
		if (err)
			return err;
		return -EIO;
	}
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	return 0;
}

/**
 * sht15_send_cmd() - Sends a command to the device.
 * @data:	device state
 * @cmd:	command byte to be sent
 *
 * On entry, sck is output low, data is output pull high
 * and the interrupt disabled.
 */
static int sht15_send_cmd(struct sht15_data *data, u8 cmd)
{
	int err;

	err = sht15_transmission_start(data);
	if (err)
		return err;
	sht15_send_byte(data, cmd);
	return sht15_wait_for_response(data);
}

/**
 * sht15_soft_reset() - send a soft reset command
 * @data:	sht15 specific data.
 *
 * As described in section 3.2 of the datasheet.
 */
static int sht15_soft_reset(struct sht15_data *data)
{
	int ret;

	ret = sht15_send_cmd(data, SHT15_SOFT_RESET);
	if (ret)
		return ret;
	msleep(SHT15_TSRST);
	/* device resets default hardware status register value */
	data->val_status = 0;

	return ret;
}

/**
 * sht15_ack() - send a ack
 * @data:	sht15 specific data.
 *
 * Each byte of data is acknowledged by pulling the data line
 * low for one clock pulse.
 */
static int sht15_ack(struct sht15_data *data)
{
	int err;

	err = gpio_direction_output(data->pdata->gpio_data, 0);
	if (err)
		return err;
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_data, 1);

	return gpio_direction_input(data->pdata->gpio_data);
}

/**
 * sht15_end_transmission() - notify device of end of transmission
 * @data:	device state.
 *
 * This is basically a NAK (single clock pulse, data high).
 */
static int sht15_end_transmission(struct sht15_data *data)
{
	int err;

	err = gpio_direction_output(data->pdata->gpio_data, 1);
	if (err)
		return err;
	ndelay(SHT15_TSU);
	gpio_set_value(data->pdata->gpio_sck, 1);
	ndelay(SHT15_TSCKH);
	gpio_set_value(data->pdata->gpio_sck, 0);
	ndelay(SHT15_TSCKL);
	return 0;
}

/**
 * sht15_read_byte() - Read a byte back from the device
 * @data:	device state.
 */
static u8 sht15_read_byte(struct sht15_data *data)
{
	int i;
	u8 byte = 0;

	for (i = 0; i < 8; ++i) {
		byte <<= 1;
		gpio_set_value(data->pdata->gpio_sck, 1);
		ndelay(SHT15_TSCKH);
		byte |= !!gpio_get_value(data->pdata->gpio_data);
		gpio_set_value(data->pdata->gpio_sck, 0);
		ndelay(SHT15_TSCKL);
	}
	return byte;
}

/**
 * sht15_send_status() - write the status register byte
 * @data:	sht15 specific data.
 * @status:	the byte to set the status register with.
 *
 * As described in figure 14 and table 5 of the datasheet.
 */
static int sht15_send_status(struct sht15_data *data, u8 status)
{
	int err;

	err = sht15_send_cmd(data, SHT15_WRITE_STATUS);
	if (err)
		return err;
	err = gpio_direction_output(data->pdata->gpio_data, 1);
	if (err)
		return err;
	ndelay(SHT15_TSU);
	sht15_send_byte(data, status);
	err = sht15_wait_for_response(data);
	if (err)
		return err;

	data->val_status = status;
	return 0;
}

/**
 * sht15_update_status() - get updated status register from device if too old
 * @data:	device instance specific data.
 *
 * As described in figure 15 and table 5 of the datasheet.
 */
static int sht15_update_status(struct sht15_data *data)
{
	int ret = 0;
	u8 status;
	u8 previous_config;
	u8 dev_checksum = 0;
	u8 checksum_vals[2];
	int timeout = HZ;

	mutex_lock(&data->read_lock);
	if (time_after(jiffies, data->last_status + timeout)
			|| !data->status_valid) {
		ret = sht15_send_cmd(data, SHT15_READ_STATUS);
		if (ret)
			goto unlock;
		status = sht15_read_byte(data);

		if (data->checksumming) {
			sht15_ack(data);
			dev_checksum = sht15_reverse(sht15_read_byte(data));
			checksum_vals[0] = SHT15_READ_STATUS;
			checksum_vals[1] = status;
			data->checksum_ok = (sht15_crc8(data, checksum_vals, 2)
					== dev_checksum);
		}

		ret = sht15_end_transmission(data);
		if (ret)
			goto unlock;

		/*
		 * Perform checksum validation on the received data.
		 * Specification mentions that in case a checksum verification
		 * fails, a soft reset command must be sent to the device.
		 */
		if (data->checksumming && !data->checksum_ok) {
			previous_config = data->val_status & 0x07;
			ret = sht15_soft_reset(data);
			if (ret)
				goto unlock;
			if (previous_config) {
				ret = sht15_send_status(data, previous_config);
				if (ret) {
					dev_err(data->dev,
						"CRC validation failed, unable "
						"to restore device settings\n");
					goto unlock;
				}
			}
			ret = -EAGAIN;
			goto unlock;
		}

		data->val_status = status;
		data->status_valid = true;
		data->last_status = jiffies;
	}

unlock:
	mutex_unlock(&data->read_lock);
	return ret;
}

/**
 * sht15_measurement() - get a new value from device
 * @data:		device instance specific data
 * @command:		command sent to request value
 * @timeout_msecs:	timeout after which comms are assumed
 *			to have failed are reset.
 */
static int sht15_measurement(struct sht15_data *data,
			     int command,
			     int timeout_msecs)
{
	int ret;
	u8 previous_config;

	ret = sht15_send_cmd(data, command);
	if (ret)
		return ret;

	ret = gpio_direction_input(data->pdata->gpio_data);
	if (ret)
		return ret;
	atomic_set(&data->interrupt_handled, 0);

	enable_irq(gpio_to_irq(data->pdata->gpio_data));
	if (gpio_get_value(data->pdata->gpio_data) == 0) {
		disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));
		/* Only relevant if the interrupt hasn't occurred. */
		if (!atomic_read(&data->interrupt_handled))
			schedule_work(&data->read_work);
	}
	ret = wait_event_timeout(data->wait_queue,
				 (data->state == SHT15_READING_NOTHING),
				 msecs_to_jiffies(timeout_msecs));
	if (data->state != SHT15_READING_NOTHING) { /* I/O error occurred */
		data->state = SHT15_READING_NOTHING;
		return -EIO;
	} else if (ret == 0) { /* timeout occurred */
		disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));
		ret = sht15_connection_reset(data);
		if (ret)
			return ret;
		return -ETIME;
	}

	/*
	 *  Perform checksum validation on the received data.
	 *  Specification mentions that in case a checksum verification fails,
	 *  a soft reset command must be sent to the device.
	 */
	if (data->checksumming && !data->checksum_ok) {
		previous_config = data->val_status & 0x07;
		ret = sht15_soft_reset(data);
		if (ret)
			return ret;
		if (previous_config) {
			ret = sht15_send_status(data, previous_config);
			if (ret) {
				dev_err(data->dev,
					"CRC validation failed, unable "
					"to restore device settings\n");
				return ret;
			}
		}
		return -EAGAIN;
	}

	return 0;
}

/**
 * sht15_update_measurements() - get updated measures from device if too old
 * @data:	device state
 */
static int sht15_update_measurements(struct sht15_data *data)
{
	int ret = 0;
	int timeout = HZ;

	mutex_lock(&data->read_lock);
	if (time_after(jiffies, data->last_measurement + timeout)
	    || !data->measurements_valid) {
		data->state = SHT15_READING_HUMID;
		ret = sht15_measurement(data, SHT15_MEASURE_RH, 160);
		if (ret)
			goto unlock;
		data->state = SHT15_READING_TEMP;
		ret = sht15_measurement(data, SHT15_MEASURE_TEMP, 400);
		if (ret)
			goto unlock;
		data->measurements_valid = true;
		data->last_measurement = jiffies;
	}

unlock:
	mutex_unlock(&data->read_lock);
	return ret;
}

/**
 * sht15_calc_temp() - convert the raw reading to a temperature
 * @data:	device state
 *
 * As per section 4.3 of the data sheet.
 */
static inline int sht15_calc_temp(struct sht15_data *data)
{
	int d1 = temppoints[0].d1;
	int d2 = (data->val_status & SHT15_STATUS_LOW_RESOLUTION) ? 40 : 10;
	int i;

	for (i = ARRAY_SIZE(temppoints) - 1; i > 0; i--)
		/* Find pointer to interpolate */
		if (data->supply_uv > temppoints[i - 1].vdd) {
			d1 = (data->supply_uv - temppoints[i - 1].vdd)
				* (temppoints[i].d1 - temppoints[i - 1].d1)
				/ (temppoints[i].vdd - temppoints[i - 1].vdd)
				+ temppoints[i - 1].d1;
			break;
		}

	return data->val_temp * d2 + d1;
}

/**
 * sht15_calc_humid() - using last temperature convert raw to humid
 * @data:	device state
 *
 * This is the temperature compensated version as per section 4.2 of
 * the data sheet.
 *
 * The sensor is assumed to be V3, which is compatible with V4.
 * Humidity conversion coefficients are shown in table 7 of the datasheet.
 */
static inline int sht15_calc_humid(struct sht15_data *data)
{
	int rh_linear; /* milli percent */
	int temp = sht15_calc_temp(data);
	int c2, c3;
	int t2;
	const int c1 = -4;

	if (data->val_status & SHT15_STATUS_LOW_RESOLUTION) {
		c2 = 648000; /* x 10 ^ -6 */
		c3 = -7200;  /* x 10 ^ -7 */
		t2 = 1280;
	} else {
		c2 = 40500;  /* x 10 ^ -6 */
		c3 = -28;    /* x 10 ^ -7 */
		t2 = 80;
	}

	rh_linear = c1 * 1000
		+ c2 * data->val_humid / 1000
		+ (data->val_humid * data->val_humid * c3) / 10000;
	return (temp - 25000) * (10000 + t2 * data->val_humid)
		/ 1000000 + rh_linear;
}

/**
 * sht15_show_status() - show status information in sysfs
 * @dev:	device.
 * @attr:	device attribute.
 * @buf:	sysfs buffer where information is written to.
 *
 * Will be called on read access to temp1_fault, humidity1_fault
 * and heater_enable sysfs attributes.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht15_show_status(struct device *dev,
				 struct device_attribute *attr,
				 char *buf)
{
	int ret;
	struct sht15_data *data = dev_get_drvdata(dev);
	u8 bit = to_sensor_dev_attr(attr)->index;

	ret = sht15_update_status(data);

	return ret ? ret : sprintf(buf, "%d\n", !!(data->val_status & bit));
}

/**
 * sht15_store_heater() - change heater state via sysfs
 * @dev:	device.
 * @attr:	device attribute.
 * @buf:	sysfs buffer to read the new heater state from.
 * @count:	length of the data.
 *
 * Will be called on write access to heater_enable sysfs attribute.
 * Returns number of bytes actually decoded, negative errno on error.
 */
static ssize_t sht15_store_heater(struct device *dev,
				  struct device_attribute *attr,
				  const char *buf, size_t count)
{
	int ret;
	struct sht15_data *data = dev_get_drvdata(dev);
	long value;
	u8 status;

	if (kstrtol(buf, 10, &value))
		return -EINVAL;

	mutex_lock(&data->read_lock);
	status = data->val_status & 0x07;
	if (!!value)
		status |= SHT15_STATUS_HEATER;
	else
		status &= ~SHT15_STATUS_HEATER;

	ret = sht15_send_status(data, status);
	mutex_unlock(&data->read_lock);

	return ret ? ret : count;
}

/**
 * sht15_show_temp() - show temperature measurement value in sysfs
 * @dev:	device.
 * @attr:	device attribute.
 * @buf:	sysfs buffer where measurement values are written to.
 *
 * Will be called on read access to temp1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht15_show_temp(struct device *dev,
			       struct device_attribute *attr,
			       char *buf)
{
	int ret;
	struct sht15_data *data = dev_get_drvdata(dev);

	/* Technically no need to read humidity as well */
	ret = sht15_update_measurements(data);

	return ret ? ret : sprintf(buf, "%d\n",
				   sht15_calc_temp(data));
}

/**
 * sht15_show_humidity() - show humidity measurement value in sysfs
 * @dev:	device.
 * @attr:	device attribute.
 * @buf:	sysfs buffer where measurement values are written to.
 *
 * Will be called on read access to humidity1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht15_show_humidity(struct device *dev,
				   struct device_attribute *attr,
				   char *buf)
{
	int ret;
	struct sht15_data *data = dev_get_drvdata(dev);

	ret = sht15_update_measurements(data);

	return ret ? ret : sprintf(buf, "%d\n", sht15_calc_humid(data));
}

static ssize_t show_name(struct device *dev,
			 struct device_attribute *attr,
			 char *buf)
{
	struct platform_device *pdev = to_platform_device(dev);
	return sprintf(buf, "%s\n", pdev->name);
}

static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
			  sht15_show_temp, NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
			  sht15_show_humidity, NULL, 0);
static SENSOR_DEVICE_ATTR(temp1_fault, S_IRUGO, sht15_show_status, NULL,
			  SHT15_STATUS_LOW_BATTERY);
static SENSOR_DEVICE_ATTR(humidity1_fault, S_IRUGO, sht15_show_status, NULL,
			  SHT15_STATUS_LOW_BATTERY);
static SENSOR_DEVICE_ATTR(heater_enable, S_IRUGO | S_IWUSR, sht15_show_status,
			  sht15_store_heater, SHT15_STATUS_HEATER);
static DEVICE_ATTR(name, S_IRUGO, show_name, NULL);
static struct attribute *sht15_attrs[] = {
	&sensor_dev_attr_temp1_input.dev_attr.attr,
	&sensor_dev_attr_humidity1_input.dev_attr.attr,
	&sensor_dev_attr_temp1_fault.dev_attr.attr,
	&sensor_dev_attr_humidity1_fault.dev_attr.attr,
	&sensor_dev_attr_heater_enable.dev_attr.attr,
	&dev_attr_name.attr,
	NULL,
};

static const struct attribute_group sht15_attr_group = {
	.attrs = sht15_attrs,
};

static irqreturn_t sht15_interrupt_fired(int irq, void *d)
{
	struct sht15_data *data = d;

	/* First disable the interrupt */
	disable_irq_nosync(irq);
	atomic_inc(&data->interrupt_handled);
	/* Then schedule a reading work struct */
	if (data->state != SHT15_READING_NOTHING)
		schedule_work(&data->read_work);
	return IRQ_HANDLED;
}

static void sht15_bh_read_data(struct work_struct *work_s)
{
	uint16_t val = 0;
	u8 dev_checksum = 0;
	u8 checksum_vals[3];
	struct sht15_data *data
		= container_of(work_s, struct sht15_data,
			       read_work);

	/* Firstly, verify the line is low */
	if (gpio_get_value(data->pdata->gpio_data)) {
		/*
		 * If not, then start the interrupt again - care here as could
		 * have gone low in meantime so verify it hasn't!
		 */
		atomic_set(&data->interrupt_handled, 0);
		enable_irq(gpio_to_irq(data->pdata->gpio_data));
		/* If still not occurred or another handler was scheduled */
		if (gpio_get_value(data->pdata->gpio_data)
		    || atomic_read(&data->interrupt_handled))
			return;
	}

	/* Read the data back from the device */
	val = sht15_read_byte(data);
	val <<= 8;
	if (sht15_ack(data))
		goto wakeup;
	val |= sht15_read_byte(data);

	if (data->checksumming) {
		/*
		 * Ask the device for a checksum and read it back.
		 * Note: the device sends the checksum byte reversed.
		 */
		if (sht15_ack(data))
			goto wakeup;
		dev_checksum = sht15_reverse(sht15_read_byte(data));
		checksum_vals[0] = (data->state == SHT15_READING_TEMP) ?
			SHT15_MEASURE_TEMP : SHT15_MEASURE_RH;
		checksum_vals[1] = (u8) (val >> 8);
		checksum_vals[2] = (u8) val;
		data->checksum_ok
			= (sht15_crc8(data, checksum_vals, 3) == dev_checksum);
	}

	/* Tell the device we are done */
	if (sht15_end_transmission(data))
		goto wakeup;

	switch (data->state) {
	case SHT15_READING_TEMP:
		data->val_temp = val;
		break;
	case SHT15_READING_HUMID:
		data->val_humid = val;
		break;
	default:
		break;
	}

	data->state = SHT15_READING_NOTHING;
wakeup:
	wake_up(&data->wait_queue);
}

static void sht15_update_voltage(struct work_struct *work_s)
{
	struct sht15_data *data
		= container_of(work_s, struct sht15_data,
			       update_supply_work);
	data->supply_uv = regulator_get_voltage(data->reg);
}

/**
 * sht15_invalidate_voltage() - mark supply voltage invalid when notified by reg
 * @nb:		associated notification structure
 * @event:	voltage regulator state change event code
 * @ignored:	function parameter - ignored here
 *
 * Note that as the notification code holds the regulator lock, we have
 * to schedule an update of the supply voltage rather than getting it directly.
 */
static int sht15_invalidate_voltage(struct notifier_block *nb,
				    unsigned long event,
				    void *ignored)
{
	struct sht15_data *data = container_of(nb, struct sht15_data, nb);

	if (event == REGULATOR_EVENT_VOLTAGE_CHANGE)
		data->supply_uv_valid = false;
	schedule_work(&data->update_supply_work);

	return NOTIFY_OK;
}

static int sht15_probe(struct platform_device *pdev)
{
	int ret;
	struct sht15_data *data;
	u8 status = 0;

	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
	if (!data)
		return -ENOMEM;

	INIT_WORK(&data->read_work, sht15_bh_read_data);
	INIT_WORK(&data->update_supply_work, sht15_update_voltage);
	platform_set_drvdata(pdev, data);
	mutex_init(&data->read_lock);
	data->dev = &pdev->dev;
	init_waitqueue_head(&data->wait_queue);

	if (pdev->dev.platform_data == NULL) {
		dev_err(&pdev->dev, "no platform data supplied\n");
		return -EINVAL;
	}
	data->pdata = pdev->dev.platform_data;
	data->supply_uv = data->pdata->supply_mv * 1000;
	if (data->pdata->checksum)
		data->checksumming = true;
	if (data->pdata->no_otp_reload)
		status |= SHT15_STATUS_NO_OTP_RELOAD;
	if (data->pdata->low_resolution)
		status |= SHT15_STATUS_LOW_RESOLUTION;

	/*
	 * If a regulator is available,
	 * query what the supply voltage actually is!
	 */
	data->reg = devm_regulator_get(data->dev, "vcc");
	if (!IS_ERR(data->reg)) {
		int voltage;

		voltage = regulator_get_voltage(data->reg);
		if (voltage)
			data->supply_uv = voltage;

		regulator_enable(data->reg);
		/*
		 * Setup a notifier block to update this if another device
		 * causes the voltage to change
		 */
		data->nb.notifier_call = &sht15_invalidate_voltage;
		ret = regulator_register_notifier(data->reg, &data->nb);
		if (ret) {
			dev_err(&pdev->dev,
				"regulator notifier request failed\n");
			regulator_disable(data->reg);
			return ret;
		}
	}

	/* Try requesting the GPIOs */
	ret = devm_gpio_request_one(&pdev->dev, data->pdata->gpio_sck,
			GPIOF_OUT_INIT_LOW, "SHT15 sck");
	if (ret) {
		dev_err(&pdev->dev, "clock line GPIO request failed\n");
		goto err_release_reg;
	}

	ret = devm_gpio_request(&pdev->dev, data->pdata->gpio_data,
				"SHT15 data");
	if (ret) {
		dev_err(&pdev->dev, "data line GPIO request failed\n");
		goto err_release_reg;
	}

	ret = devm_request_irq(&pdev->dev, gpio_to_irq(data->pdata->gpio_data),
			       sht15_interrupt_fired,
			       IRQF_TRIGGER_FALLING,
			       "sht15 data",
			       data);
	if (ret) {
		dev_err(&pdev->dev, "failed to get irq for data line\n");
		goto err_release_reg;
	}
	disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));
	ret = sht15_connection_reset(data);
	if (ret)
		goto err_release_reg;
	ret = sht15_soft_reset(data);
	if (ret)
		goto err_release_reg;

	/* write status with platform data options */
	if (status) {
		ret = sht15_send_status(data, status);
		if (ret)
			goto err_release_reg;
	}

	ret = sysfs_create_group(&pdev->dev.kobj, &sht15_attr_group);
	if (ret) {
		dev_err(&pdev->dev, "sysfs create failed\n");
		goto err_release_reg;
	}

	data->hwmon_dev = hwmon_device_register(data->dev);
	if (IS_ERR(data->hwmon_dev)) {
		ret = PTR_ERR(data->hwmon_dev);
		goto err_release_sysfs_group;
	}

	return 0;

err_release_sysfs_group:
	sysfs_remove_group(&pdev->dev.kobj, &sht15_attr_group);
err_release_reg:
	if (!IS_ERR(data->reg)) {
		regulator_unregister_notifier(data->reg, &data->nb);
		regulator_disable(data->reg);
	}
	return ret;
}

static int sht15_remove(struct platform_device *pdev)
{
	struct sht15_data *data = platform_get_drvdata(pdev);

	/*
	 * Make sure any reads from the device are done and
	 * prevent new ones beginning
	 */
	mutex_lock(&data->read_lock);
	if (sht15_soft_reset(data)) {
		mutex_unlock(&data->read_lock);
		return -EFAULT;
	}
	hwmon_device_unregister(data->hwmon_dev);
	sysfs_remove_group(&pdev->dev.kobj, &sht15_attr_group);
	if (!IS_ERR(data->reg)) {
		regulator_unregister_notifier(data->reg, &data->nb);
		regulator_disable(data->reg);
	}

	mutex_unlock(&data->read_lock);

	return 0;
}

static struct platform_device_id sht15_device_ids[] = {
	{ "sht10", sht10 },
	{ "sht11", sht11 },
	{ "sht15", sht15 },
	{ "sht71", sht71 },
	{ "sht75", sht75 },
	{ }
};
MODULE_DEVICE_TABLE(platform, sht15_device_ids);

static struct platform_driver sht15_driver = {
	.driver = {
		.name = "sht15",
		.owner = THIS_MODULE,
	},
	.probe = sht15_probe,
	.remove = sht15_remove,
	.id_table = sht15_device_ids,
};
module_platform_driver(sht15_driver);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Sensirion SHT15 temperature and humidity sensor driver");