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lm70.c

/*
 * lm70.c
 *
 * The LM70 is a temperature sensor chip from National Semiconductor (NS).
 * Copyright (C) 2006 Kaiwan N Billimoria <kaiwan@designergraphix.com>
 *
 * The LM70 communicates with a host processor via an SPI/Microwire Bus
 * interface. The complete datasheet is available at National's website
 * here:
 * http://www.national.com/pf/LM/LM70.html
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/sysfs.h>
#include <linux/hwmon.h>
#include <linux/mutex.h>
#include <linux/spi/spi.h>


#define DRVNAME         "lm70"

struct lm70 {
      struct device *hwmon_dev;
      struct mutex lock;
};

/* sysfs hook function */
static ssize_t lm70_sense_temp(struct device *dev,
            struct device_attribute *attr, char *buf)
{
      struct spi_device *spi = to_spi_device(dev);
      int status, val;
      u8 rxbuf[2];
      s16 raw=0;
      struct lm70 *p_lm70 = dev_get_drvdata(&spi->dev);

      if (mutex_lock_interruptible(&p_lm70->lock))
            return -ERESTARTSYS;

      /*
       * spi_read() requires a DMA-safe buffer; so we use
       * spi_write_then_read(), transmitting 0 bytes.
       */
      status = spi_write_then_read(spi, NULL, 0, &rxbuf[0], 2);
      if (status < 0) {
            printk(KERN_WARNING
            "spi_write_then_read failed with status %d\n", status);
            goto out;
      }
      dev_dbg(dev, "rxbuf[1] : 0x%x rxbuf[0] : 0x%x\n", rxbuf[1], rxbuf[0]);

      raw = (rxbuf[1] << 8) + rxbuf[0];
      dev_dbg(dev, "raw=0x%x\n", raw);

      /*
       * The "raw" temperature read into rxbuf[] is a 16-bit signed 2's
       * complement value. Only the MSB 11 bits (1 sign + 10 temperature
       * bits) are meaningful; the LSB 5 bits are to be discarded.
       * See the datasheet.
       *
       * Further, each bit represents 0.25 degrees Celsius; so, multiply
       * by 0.25. Also multiply by 1000 to represent in millidegrees
       * Celsius.
       * So it's equivalent to multiplying by 0.25 * 1000 = 250.
       */
      val = ((int)raw/32) * 250;
      status = sprintf(buf, "%d\n", val); /* millidegrees Celsius */
out:
      mutex_unlock(&p_lm70->lock);
      return status;
}

static DEVICE_ATTR(temp1_input, S_IRUGO, lm70_sense_temp, NULL);

static ssize_t lm70_show_name(struct device *dev, struct device_attribute
                        *devattr, char *buf)
{
      return sprintf(buf, "lm70\n");
}

static DEVICE_ATTR(name, S_IRUGO, lm70_show_name, NULL);

/*----------------------------------------------------------------------*/

static int __devinit lm70_probe(struct spi_device *spi)
{
      struct lm70 *p_lm70;
      int status;

      /* signaling is SPI_MODE_0 on a 3-wire link (shared SI/SO) */
      if ((spi->mode & (SPI_CPOL|SPI_CPHA)) || !(spi->mode & SPI_3WIRE))
            return -EINVAL;

      p_lm70 = kzalloc(sizeof *p_lm70, GFP_KERNEL);
      if (!p_lm70)
            return -ENOMEM;

      mutex_init(&p_lm70->lock);

      /* sysfs hook */
      p_lm70->hwmon_dev = hwmon_device_register(&spi->dev);
      if (IS_ERR(p_lm70->hwmon_dev)) {
            dev_dbg(&spi->dev, "hwmon_device_register failed.\n");
            status = PTR_ERR(p_lm70->hwmon_dev);
            goto out_dev_reg_failed;
      }
      dev_set_drvdata(&spi->dev, p_lm70);

      if ((status = device_create_file(&spi->dev, &dev_attr_temp1_input))
       || (status = device_create_file(&spi->dev, &dev_attr_name))) {
            dev_dbg(&spi->dev, "device_create_file failure.\n");
            goto out_dev_create_file_failed;
      }

      return 0;

out_dev_create_file_failed:
      device_remove_file(&spi->dev, &dev_attr_temp1_input);
      hwmon_device_unregister(p_lm70->hwmon_dev);
out_dev_reg_failed:
      dev_set_drvdata(&spi->dev, NULL);
      kfree(p_lm70);
      return status;
}

static int __devexit lm70_remove(struct spi_device *spi)
{
      struct lm70 *p_lm70 = dev_get_drvdata(&spi->dev);

      device_remove_file(&spi->dev, &dev_attr_temp1_input);
      device_remove_file(&spi->dev, &dev_attr_name);
      hwmon_device_unregister(p_lm70->hwmon_dev);
      dev_set_drvdata(&spi->dev, NULL);
      kfree(p_lm70);

      return 0;
}

static struct spi_driver lm70_driver = {
      .driver = {
            .name = "lm70",
            .owner      = THIS_MODULE,
      },
      .probe      = lm70_probe,
      .remove     = __devexit_p(lm70_remove),
};

static int __init init_lm70(void)
{
      return spi_register_driver(&lm70_driver);
}

static void __exit cleanup_lm70(void)
{
      spi_unregister_driver(&lm70_driver);
}

module_init(init_lm70);
module_exit(cleanup_lm70);

MODULE_AUTHOR("Kaiwan N Billimoria");
MODULE_DESCRIPTION("National Semiconductor LM70 Linux driver");
MODULE_LICENSE("GPL");

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