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ds1374.c

/*
 * drivers/i2c/chips/ds1374.c
 *
 * I2C client/driver for the Maxim/Dallas DS1374 Real-Time Clock
 *
 * Author: Randy Vinson <rvinson@mvista.com>
 *
 * Based on the m41t00.c by Mark Greer <mgreer@mvista.com>
 *
 * 2005 (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.
 */
/*
 * This i2c client/driver wedges between the drivers/char/genrtc.c RTC
 * interface and the SMBus interface of the i2c subsystem.
 * It would be more efficient to use i2c msgs/i2c_transfer directly but, as
 * recommened in .../Documentation/i2c/writing-clients section
 * "Sending and receiving", using SMBus level communication is preferred.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/i2c.h>
#include <linux/rtc.h>
#include <linux/bcd.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>

#define DS1374_REG_TOD0       0x00
#define DS1374_REG_TOD1       0x01
#define DS1374_REG_TOD2       0x02
#define DS1374_REG_TOD3       0x03
#define DS1374_REG_WDALM0     0x04
#define DS1374_REG_WDALM1     0x05
#define DS1374_REG_WDALM2     0x06
#define DS1374_REG_CR         0x07
#define DS1374_REG_SR         0x08
#define DS1374_REG_SR_OSF     0x80
#define DS1374_REG_TCR        0x09

#define     DS1374_DRV_NAME         "ds1374"

static DEFINE_MUTEX(ds1374_mutex);

static struct i2c_driver ds1374_driver;
static struct i2c_client *save_client;

static unsigned short ignore[] = { I2C_CLIENT_END };
static unsigned short normal_addr[] = { 0x68, I2C_CLIENT_END };

static struct i2c_client_address_data addr_data = {
      .normal_i2c = normal_addr,
      .probe = ignore,
      .ignore = ignore,
};

static ulong ds1374_read_rtc(void)
{
      ulong time = 0;
      int reg = DS1374_REG_WDALM0;

      while (reg--) {
            s32 tmp;
            if ((tmp = i2c_smbus_read_byte_data(save_client, reg)) < 0) {
                  dev_warn(&save_client->dev,
                         "can't read from rtc chip\n");
                  return 0;
            }
            time = (time << 8) | (tmp & 0xff);
      }
      return time;
}

static void ds1374_write_rtc(ulong time)
{
      int reg;

      for (reg = DS1374_REG_TOD0; reg < DS1374_REG_WDALM0; reg++) {
            if (i2c_smbus_write_byte_data(save_client, reg, time & 0xff)
                < 0) {
                  dev_warn(&save_client->dev,
                         "can't write to rtc chip\n");
                  break;
            }
            time = time >> 8;
      }
}

static void ds1374_check_rtc_status(void)
{
      s32 tmp;

      tmp = i2c_smbus_read_byte_data(save_client, DS1374_REG_SR);
      if (tmp < 0) {
            dev_warn(&save_client->dev,
                   "can't read status from rtc chip\n");
            return;
      }
      if (tmp & DS1374_REG_SR_OSF) {
            dev_warn(&save_client->dev,
                   "oscillator discontinuity flagged, time unreliable\n");
            tmp &= ~DS1374_REG_SR_OSF;
            tmp = i2c_smbus_write_byte_data(save_client, DS1374_REG_SR,
                                    tmp & 0xff);
            if (tmp < 0)
                  dev_warn(&save_client->dev,
                         "can't clear discontinuity notification\n");
      }
}

ulong ds1374_get_rtc_time(void)
{
      ulong t1, t2;
      int limit = 10;         /* arbitrary retry limit */

      mutex_lock(&ds1374_mutex);

      /*
       * Since the reads are being performed one byte at a time using
       * the SMBus vs a 4-byte i2c transfer, there is a chance that a
       * carry will occur during the read. To detect this, 2 reads are
       * performed and compared.
       */
      do {
            t1 = ds1374_read_rtc();
            t2 = ds1374_read_rtc();
      } while (t1 != t2 && limit--);

      mutex_unlock(&ds1374_mutex);

      if (t1 != t2) {
            dev_warn(&save_client->dev,
                   "can't get consistent time from rtc chip\n");
            t1 = 0;
      }

      return t1;
}

static ulong new_time;

static void ds1374_set_work(struct work_struct *work)
{
      ulong t1, t2;
      int limit = 10;         /* arbitrary retry limit */

      t1 = new_time;

      mutex_lock(&ds1374_mutex);

      /*
       * Since the writes are being performed one byte at a time using
       * the SMBus vs a 4-byte i2c transfer, there is a chance that a
       * carry will occur during the write. To detect this, the write
       * value is read back and compared.
       */
      do {
            ds1374_write_rtc(t1);
            t2 = ds1374_read_rtc();
      } while (t1 != t2 && limit--);

      mutex_unlock(&ds1374_mutex);

      if (t1 != t2)
            dev_warn(&save_client->dev,
                   "can't confirm time set from rtc chip\n");
}

static struct workqueue_struct *ds1374_workqueue;

static DECLARE_WORK(ds1374_work, ds1374_set_work);

int ds1374_set_rtc_time(ulong nowtime)
{
      new_time = nowtime;

      if (in_interrupt())
            queue_work(ds1374_workqueue, &ds1374_work);
      else
            ds1374_set_work(NULL);

      return 0;
}

/*
 *****************************************************************************
 *
 *    Driver Interface
 *
 *****************************************************************************
 */
static int ds1374_probe(struct i2c_adapter *adap, int addr, int kind)
{
      struct i2c_client *client;
      int rc;

      client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
      if (!client)
            return -ENOMEM;

      strncpy(client->name, DS1374_DRV_NAME, I2C_NAME_SIZE);
      client->addr = addr;
      client->adapter = adap;
      client->driver = &ds1374_driver;

      ds1374_workqueue = create_singlethread_workqueue("ds1374");
      if (!ds1374_workqueue) {
            kfree(client);
            return -ENOMEM;   /* most expected reason */
      }

      if ((rc = i2c_attach_client(client)) != 0) {
            kfree(client);
            return rc;
      }

      save_client = client;

      ds1374_check_rtc_status();

      return 0;
}

static int ds1374_attach(struct i2c_adapter *adap)
{
      return i2c_probe(adap, &addr_data, ds1374_probe);
}

static int ds1374_detach(struct i2c_client *client)
{
      int rc;

      if ((rc = i2c_detach_client(client)) == 0) {
            kfree(i2c_get_clientdata(client));
            destroy_workqueue(ds1374_workqueue);
      }
      return rc;
}

static struct i2c_driver ds1374_driver = {
      .driver = {
            .name = DS1374_DRV_NAME,
      },
      .id = I2C_DRIVERID_DS1374,
      .attach_adapter = ds1374_attach,
      .detach_client = ds1374_detach,
};

static int __init ds1374_init(void)
{
      return i2c_add_driver(&ds1374_driver);
}

static void __exit ds1374_exit(void)
{
      i2c_del_driver(&ds1374_driver);
}

module_init(ds1374_init);
module_exit(ds1374_exit);

MODULE_AUTHOR("Randy Vinson <rvinson@mvista.com>");
MODULE_DESCRIPTION("Maxim/Dallas DS1374 RTC I2C Client Driver");
MODULE_LICENSE("GPL");

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