rtc-ds13307/rtc-ds13307.c

/*
 * rtc-ds13307.c - RTC driver for the DS1307 and DS13307 I2C chips.
 *
 * Copyright (C) 2018 Helmut Pozimski
 *
 * 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.
 */

#include <linux/module.h>
#include <linux/rtc.h>
#include <linux/i2c.h>

#define M_NAME "rtc-ds13307" /* Module name */

#define DEVICE_DS1307 1
#define DEVICE_DS1337 2

#define DS1307_SEC 0x00
#define DS1307_MAX_ADDR 0x3F

#define DS1337_CTL 0x0E
#define DS1337_STAT 0x0F

static int model_detected;

static const struct rtc_class_ops ds13307_rtc_ops = {
};

/* Reads a single byte via i2c, returns 0 on success */
static int ds13307_read_single_byte(struct i2c_client *client,
		unsigned char *addr, u8 *byte) {
	int r;
	struct i2c_msg msgs[] = {
		{
			.addr = client->addr,
			.len = 1,
			.buf = addr
		},
		{
			.addr = client->addr,
			.flags = I2C_M_RD,
			.len = 1,
			.buf = byte
		}
	};
	r = i2c_transfer(client->adapter, msgs, 2);
	if (r == 2) {
		return 0;
	} else {
		return r;
	}
}

/* Performs the device detection to distinguish between the
 * DS1307 and DS1337 chips. Returns the defined device ID or
 * -1 on failure
 */
static int ds13307_detect_device(struct i2c_client *client) {
	u8 data;
	int result;
	unsigned char addr = DS1307_MAX_ADDR;
	result = ds13307_read_single_byte(client, &addr, &data);
	if (!result) {
		printk(KERN_INFO "%s: Detected device DS1307\n", M_NAME);
		return DEVICE_DS1307;
	}
        addr = DS1337_CTL;
	result = ds13307_read_single_byte(client, &addr, &data);
	if (!result) {	
		printk(KERN_INFO "%s: Detected device DS1337\n", M_NAME);
 		return DEVICE_DS1337;
	}
	printk(KERN_ERR "%s: Could not talk to I2C device at addr %x, is it connected?\n",
			M_NAME, client->addr);
	return -1;
}

/* The oscillator is stopped for both chips when power is first applied,
 * therefore this function checks its status and clears the stop bit.
 */
static int ds13307_start_oscillator(struct i2c_client *client) {
	u8 data;
	int r, v;
       	unsigned char addr;
	char buf[2];
	if (model_detected == DEVICE_DS1307) {
		addr = DS1307_SEC;
	} else {
		addr = DS1337_STAT;
	}
	r = ds13307_read_single_byte(client, &addr, &data);
	if (data & 0x80) {
		buf[0] = addr;
		buf[1] = data ^ 0x80;
		v = i2c_master_send(client, buf, 2);
	} else {
		v = 2;
	}
	if ((r<0) || (v!=2)) {
		return -EIO;
	}
	return 0;	
}

static int ds13307_probe(struct i2c_client *client,
		const struct i2c_device_id *id) {
	model_detected = ds13307_detect_device(client);
	if ((model_detected != DEVICE_DS1307) && (model_detected != DEVICE_DS1337)) {
		return -EIO;
	}
	if (ds13307_start_oscillator(client)) {
		printk(KERN_ERR "%s: failed to initialize the oscillator\n", M_NAME);
		return -EIO;
	} else {
		printk(KERN_DEBUG "%s: oscillator stop bit successfully cleared\n", M_NAME);
	}
	return 0;
}

static struct i2c_device_id ds13307_idtable[] = {
	{ "ds1307", 0 }, {}
};
MODULE_DEVICE_TABLE(i2c, ds13307_idtable);

static struct of_device_id ds13307_of_match[] = {
	{ .compatible = "dallas,ds1307" },
	{}
};
MODULE_DEVICE_TABLE(of, ds13307_of_match);

static struct i2c_driver ds13307_driver = {
	.driver = {
		.name = "rtc-ds13307",
		.of_match_table = of_match_ptr(ds13307_of_match),
	},
	.id_table = ds13307_idtable,
	.probe = ds13307_probe,
};

module_i2c_driver(ds13307_driver);

MODULE_AUTHOR("Helmut Pozimski <helmut@pozimski.eu>");
MODULE_DESCRIPTION("DS1307 and DS1337 RTC driver");
MODULE_LICENSE("GPL");