rtc-max6900.c

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/*
 * rtc class driver for the Maxim MAX6900 chip
 *
 * Author: Dale Farnsworth <[email protected]>
 *
 * based on previously existing rtc class drivers
 *
 * 2007 (c) MontaVista, Software, Inc.  This file is licensed under
 * the terms of the GNU General Public License version 2.  This program
 * is licensed "as is" without any warranty of any kind, whether express
 * or implied.
 */

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

#define DRV_VERSION "0.2"

/*
 * register indices
 */
#define MAX6900_REG_SC          0   /* seconds      00-59 */
#define MAX6900_REG_MN          1   /* minutes      00-59 */
#define MAX6900_REG_HR          2   /* hours        00-23 */
#define MAX6900_REG_DT          3   /* day of month 00-31 */
#define MAX6900_REG_MO          4   /* month        01-12 */
#define MAX6900_REG_DW          5   /* day of week   1-7  */
#define MAX6900_REG_YR          6   /* year         00-99 */
#define MAX6900_REG_CT          7   /* control */
                        /* register 8 is undocumented */
#define MAX6900_REG_CENTURY     9   /* century */
#define MAX6900_REG_LEN         10

#define MAX6900_BURST_LEN       8   /* can burst r/w first 8 regs */

#define MAX6900_REG_CT_WP       (1 << 7)    /* Write Protect */

/*
 * register read/write commands
 */
#define MAX6900_REG_CONTROL_WRITE   0x8e
#define MAX6900_REG_CENTURY_WRITE   0x92
#define MAX6900_REG_CENTURY_READ    0x93
#define MAX6900_REG_RESERVED_READ   0x96
#define MAX6900_REG_BURST_WRITE     0xbe
#define MAX6900_REG_BURST_READ      0xbf

#define MAX6900_IDLE_TIME_AFTER_WRITE   3   /* specification says 2.5 mS */

static struct i2c_driver max6900_driver;

static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
{
    u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
    u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
    struct i2c_msg msgs[4] = {
        {
         .addr = client->addr,
         .flags = 0,    /* write */
         .len = sizeof(reg_burst_read),
         .buf = reg_burst_read}
        ,
        {
         .addr = client->addr,
         .flags = I2C_M_RD,
         .len = MAX6900_BURST_LEN,
         .buf = buf}
        ,
        {
         .addr = client->addr,
         .flags = 0,    /* write */
         .len = sizeof(reg_century_read),
         .buf = reg_century_read}
        ,
        {
         .addr = client->addr,
         .flags = I2C_M_RD,
         .len = sizeof(buf[MAX6900_REG_CENTURY]),
         .buf = &buf[MAX6900_REG_CENTURY]
         }
    };
    int rc;

    rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
    if (rc != ARRAY_SIZE(msgs)) {
        dev_err(&client->dev, "%s: register read failed\n", __func__);
        return -EIO;
    }
    return 0;
}

static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
{
    u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
    struct i2c_msg century_msgs[1] = {
        {
         .addr = client->addr,
         .flags = 0,    /* write */
         .len = sizeof(i2c_century_buf),
         .buf = i2c_century_buf}
    };
    u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
    struct i2c_msg burst_msgs[1] = {
        {
         .addr = client->addr,
         .flags = 0,    /* write */
         .len = sizeof(i2c_burst_buf),
         .buf = i2c_burst_buf}
    };
    int rc;

    /*
     * We have to make separate calls to i2c_transfer because of
     * the need to delay after each write to the chip.  Also,
     * we write the century byte first, since we set the write-protect
     * bit as part of the burst write.
     */
    i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];

    rc = i2c_transfer(client->adapter, century_msgs,
              ARRAY_SIZE(century_msgs));
    if (rc != ARRAY_SIZE(century_msgs))
        goto write_failed;

    msleep(MAX6900_IDLE_TIME_AFTER_WRITE);

    memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);

    rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
    if (rc != ARRAY_SIZE(burst_msgs))
        goto write_failed;
    msleep(MAX6900_IDLE_TIME_AFTER_WRITE);

    return 0;

 write_failed:
    dev_err(&client->dev, "%s: register write failed\n", __func__);
    return -EIO;
}

static int max6900_i2c_read_time(struct i2c_client *client, struct rtc_time *tm)
{
    int rc;
    u8 regs[MAX6900_REG_LEN];

    rc = max6900_i2c_read_regs(client, regs);
    if (rc < 0)
        return rc;

    tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
    tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
    tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
    tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
    tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
    tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
              bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
    tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);

    return rtc_valid_tm(tm);
}

static int max6900_i2c_clear_write_protect(struct i2c_client *client)
{
    int rc;
    rc = i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
    if (rc < 0) {
        dev_err(&client->dev, "%s: control register write failed\n",
            __func__);
        return -EIO;
    }
    return 0;
}

static int
max6900_i2c_set_time(struct i2c_client *client, struct rtc_time const *tm)
{
    u8 regs[MAX6900_REG_LEN];
    int rc;

    rc = max6900_i2c_clear_write_protect(client);
    if (rc < 0)
        return rc;

    regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
    regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
    regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
    regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
    regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
    regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
    regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
    regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
    /* set write protect */
    regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;

    rc = max6900_i2c_write_regs(client, regs);
    if (rc < 0)
        return rc;

    return 0;
}

static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
{
    return max6900_i2c_read_time(to_i2c_client(dev), tm);
}

static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
{
    return max6900_i2c_set_time(to_i2c_client(dev), tm);
}

static int max6900_remove(struct i2c_client *client)
{
    struct rtc_device *rtc = i2c_get_clientdata(client);

    if (rtc)
        rtc_device_unregister(rtc);

    return 0;
}

static const struct rtc_class_ops max6900_rtc_ops = {
    .read_time = max6900_rtc_read_time,
    .set_time = max6900_rtc_set_time,
};

static int
max6900_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
    struct rtc_device *rtc;

    if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
        return -ENODEV;

    dev_info(&client->dev, "chip found, driver version " DRV_VERSION "\n");

    rtc = rtc_device_register(max6900_driver.driver.name,
                  &client->dev, &max6900_rtc_ops, THIS_MODULE);
    if (IS_ERR(rtc))
        return PTR_ERR(rtc);

    i2c_set_clientdata(client, rtc);

    return 0;
}

static struct i2c_device_id max6900_id[] = {
    { "max6900", 0 },
    { }
};

static struct i2c_driver max6900_driver = {
    .driver = {
           .name = "rtc-max6900",
           },
    .probe = max6900_probe,
    .remove = max6900_remove,
    .id_table = max6900_id,
};

module_i2c_driver(max6900_driver);

MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
MODULE_AUTHOR("Dale Farnsworth <[email protected]>");
MODULE_LICENSE("GPL");
MODULE_VERSION(DRV_VERSION);