path: root/drivers/hwmon/sht15.c

/*
 * sht15.c - support for the SHT15 Temperature and Humidity Sensor
 *
 * Portions Copyright (c) 2010-2011 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_device.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/err.h>
#include <linux/sht15.h>
#include <linux/regulator/consumer.h>
#include <linux/slab.h>
#include <asm/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

/* 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