drivers/iio/magnetometer/ak8975.c - kernel/msm-4.9 - Gitiles

 /*
  * A sensor driver for the magnetometer AK8975.
  *
  * Magnetic compass sensor driver for monitoring magnetic flux information.
  *
  * Copyright (c) 2010, NVIDIA Corporation.
  *
  * 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.,
  * 51 Franklin Street, Fifth Floor, Boston, MA	02110-1301, USA.
  */

 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/i2c.h>
 #include <linux/err.h>
 #include <linux/mutex.h>
 #include <linux/delay.h>

 #include <linux/gpio.h>

 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 /*
  * Register definitions, as well as various shifts and masks to get at the
  * individual fields of the registers.
  */
 #define AK8975_REG_WIA			0x00
 #define AK8975_DEVICE_ID		0x48

 #define AK8975_REG_INFO			0x01

 #define AK8975_REG_ST1			0x02
 #define AK8975_REG_ST1_DRDY_SHIFT	0
 #define AK8975_REG_ST1_DRDY_MASK	(1 << AK8975_REG_ST1_DRDY_SHIFT)

 #define AK8975_REG_HXL			0x03
 #define AK8975_REG_HXH			0x04
 #define AK8975_REG_HYL			0x05
 #define AK8975_REG_HYH			0x06
 #define AK8975_REG_HZL			0x07
 #define AK8975_REG_HZH			0x08
 #define AK8975_REG_ST2			0x09
 #define AK8975_REG_ST2_DERR_SHIFT	2
 #define AK8975_REG_ST2_DERR_MASK	(1 << AK8975_REG_ST2_DERR_SHIFT)

 #define AK8975_REG_ST2_HOFL_SHIFT	3
 #define AK8975_REG_ST2_HOFL_MASK	(1 << AK8975_REG_ST2_HOFL_SHIFT)

 #define AK8975_REG_CNTL			0x0A
 #define AK8975_REG_CNTL_MODE_SHIFT	0
 #define AK8975_REG_CNTL_MODE_MASK	(0xF << AK8975_REG_CNTL_MODE_SHIFT)
 #define AK8975_REG_CNTL_MODE_POWER_DOWN	0
 #define AK8975_REG_CNTL_MODE_ONCE	1
 #define AK8975_REG_CNTL_MODE_SELF_TEST	8
 #define AK8975_REG_CNTL_MODE_FUSE_ROM	0xF

 #define AK8975_REG_RSVC			0x0B
 #define AK8975_REG_ASTC			0x0C
 #define AK8975_REG_TS1			0x0D
 #define AK8975_REG_TS2			0x0E
 #define AK8975_REG_I2CDIS		0x0F
 #define AK8975_REG_ASAX			0x10
 #define AK8975_REG_ASAY			0x11
 #define AK8975_REG_ASAZ			0x12

 #define AK8975_MAX_REGS			AK8975_REG_ASAZ

 /*
  * Miscellaneous values.
  */
 #define AK8975_MAX_CONVERSION_TIMEOUT	500
 #define AK8975_CONVERSION_DONE_POLL_TIME 10

 /*
  * Per-instance context data for the device.
  */
 struct ak8975_data {
 	struct i2c_client	*client;
 	struct attribute_group	attrs;
 	struct mutex		lock;
 	u8			asa[3];
 	long			raw_to_gauss[3];
 	u8			reg_cache[AK8975_MAX_REGS];
 	int			eoc_gpio;
 };

 static const int ak8975_index_to_reg[] = {
 	AK8975_REG_HXL, AK8975_REG_HYL, AK8975_REG_HZL,
 };

 /*
  * Helper function to write to the I2C device's registers.
  */
 static int ak8975_write_data(struct i2c_client *client,
 			     u8 reg, u8 val, u8 mask, u8 shift)
 {
 	struct iio_dev *indio_dev = i2c_get_clientdata(client);
 	struct ak8975_data *data = iio_priv(indio_dev);
 	u8 regval;
 	int ret;

 	regval = (data->reg_cache[reg] & ~mask) | (val << shift);
 	ret = i2c_smbus_write_byte_data(client, reg, regval);
 	if (ret < 0) {
 		dev_err(&client->dev, "Write to device fails status %x\n", ret);
 		return ret;
 	}
 	data->reg_cache[reg] = regval;

 	return 0;
 }

 /*
  * Perform some start-of-day setup, including reading the asa calibration
  * values and caching them.
  */
 static int ak8975_setup(struct i2c_client *client)
 {
 	struct iio_dev *indio_dev = i2c_get_clientdata(client);
 	struct ak8975_data *data = iio_priv(indio_dev);
 	u8 device_id;
 	int ret;

 	/* Confirm that the device we're talking to is really an AK8975. */
 	ret = i2c_smbus_read_byte_data(client, AK8975_REG_WIA);
 	if (ret < 0) {
 		dev_err(&client->dev, "Error reading WIA\n");
 		return ret;
 	}
 	device_id = ret;
 	if (device_id != AK8975_DEVICE_ID) {
 		dev_err(&client->dev, "Device ak8975 not found\n");
 		return -ENODEV;
 	}

 	/* Write the fused rom access mode. */
 	ret = ak8975_write_data(client,
 				AK8975_REG_CNTL,
 				AK8975_REG_CNTL_MODE_FUSE_ROM,
 				AK8975_REG_CNTL_MODE_MASK,
 				AK8975_REG_CNTL_MODE_SHIFT);
 	if (ret < 0) {
 		dev_err(&client->dev, "Error in setting fuse access mode\n");
 		return ret;
 	}

 	/* Get asa data and store in the device data. */
 	ret = i2c_smbus_read_i2c_block_data(client, AK8975_REG_ASAX,
 					    3, data->asa);
 	if (ret < 0) {
 		dev_err(&client->dev, "Not able to read asa data\n");
 		return ret;
 	}

 	/* After reading fuse ROM data set power-down mode */
 	ret = ak8975_write_data(client,
 				AK8975_REG_CNTL,
 				AK8975_REG_CNTL_MODE_POWER_DOWN,
 				AK8975_REG_CNTL_MODE_MASK,
 				AK8975_REG_CNTL_MODE_SHIFT);
 	if (ret < 0) {
 		dev_err(&client->dev, "Error in setting power-down mode\n");
 		return ret;
 	}

 /*
  * Precalculate scale factor (in Gauss units) for each axis and
  * store in the device data.
  *
  * This scale factor is axis-dependent, and is derived from 3 calibration
  * factors ASA(x), ASA(y), and ASA(z).
  *
  * These ASA values are read from the sensor device at start of day, and
  * cached in the device context struct.
  *
  * Adjusting the flux value with the sensitivity adjustment value should be
  * done via the following formula:
  *
  * Hadj = H * ( ( ( (ASA-128)*0.5 ) / 128 ) + 1 )
  *
  * where H is the raw value, ASA is the sensitivity adjustment, and Hadj
  * is the resultant adjusted value.
  *
  * We reduce the formula to:
  *
  * Hadj = H * (ASA + 128) / 256
  *
  * H is in the range of -4096 to 4095.  The magnetometer has a range of
  * +-1229uT.  To go from the raw value to uT is:
  *
  * HuT = H * 1229/4096, or roughly, 3/10.
  *
  * Since 1uT = 100 gauss, our final scale factor becomes:
  *
  * Hadj = H * ((ASA + 128) / 256) * 3/10 * 100
  * Hadj = H * ((ASA + 128) * 30 / 256
  *
  * Since ASA doesn't change, we cache the resultant scale factor into the
  * device context in ak8975_setup().
  */
 	data->raw_to_gauss[0] = ((data->asa[0] + 128) * 30) >> 8;
 	data->raw_to_gauss[1] = ((data->asa[1] + 128) * 30) >> 8;
 	data->raw_to_gauss[2] = ((data->asa[2] + 128) * 30) >> 8;

 	return 0;
 }

 static int wait_conversion_complete_gpio(struct ak8975_data *data)
 {
 	struct i2c_client *client = data->client;
 	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
 	int ret;

 	/* Wait for the conversion to complete. */
 	while (timeout_ms) {
 		msleep(AK8975_CONVERSION_DONE_POLL_TIME);
 		if (gpio_get_value(data->eoc_gpio))
 			break;
 		timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
 	}
 	if (!timeout_ms) {
 		dev_err(&client->dev, "Conversion timeout happened\n");
 		return -EINVAL;
 	}

 	ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST1);
 	if (ret < 0)
 		dev_err(&client->dev, "Error in reading ST1\n");

 	return ret;
 }

 static int wait_conversion_complete_polled(struct ak8975_data *data)
 {
 	struct i2c_client *client = data->client;
 	u8 read_status;
 	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
 	int ret;

 	/* Wait for the conversion to complete. */
 	while (timeout_ms) {
 		msleep(AK8975_CONVERSION_DONE_POLL_TIME);
 		ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST1);
 		if (ret < 0) {
 			dev_err(&client->dev, "Error in reading ST1\n");
 			return ret;
 		}
 		read_status = ret;
 		if (read_status)
 			break;
 		timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
 	}
 	if (!timeout_ms) {
 		dev_err(&client->dev, "Conversion timeout happened\n");
 		return -EINVAL;
 	}
 	return read_status;
 }

 /*
  * Emits the raw flux value for the x, y, or z axis.
  */
 static int ak8975_read_axis(struct iio_dev *indio_dev, int index, int *val)
 {
 	struct ak8975_data *data = iio_priv(indio_dev);
 	struct i2c_client *client = data->client;
 	u16 meas_reg;
 	s16 raw;
 	int ret;

 	mutex_lock(&data->lock);

 	/* Set up the device for taking a sample. */
 	ret = ak8975_write_data(client,
 				AK8975_REG_CNTL,
 				AK8975_REG_CNTL_MODE_ONCE,
 				AK8975_REG_CNTL_MODE_MASK,
 				AK8975_REG_CNTL_MODE_SHIFT);
 	if (ret < 0) {
 		dev_err(&client->dev, "Error in setting operating mode\n");
 		goto exit;
 	}

 	/* Wait for the conversion to complete. */
 	if (gpio_is_valid(data->eoc_gpio))
 		ret = wait_conversion_complete_gpio(data);
 	else
 		ret = wait_conversion_complete_polled(data);
 	if (ret < 0)
 		goto exit;

 	if (ret & AK8975_REG_ST1_DRDY_MASK) {
 		ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST2);
 		if (ret < 0) {
 			dev_err(&client->dev, "Error in reading ST2\n");
 			goto exit;
 		}
 		if (ret & (AK8975_REG_ST2_DERR_MASK |
 			   AK8975_REG_ST2_HOFL_MASK)) {
 			dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
 			ret = -EINVAL;
 			goto exit;
 		}
 	}

 	/* Read the flux value from the appropriate register
 	   (the register is specified in the iio device attributes). */
 	ret = i2c_smbus_read_word_data(client, ak8975_index_to_reg[index]);
 	if (ret < 0) {
 		dev_err(&client->dev, "Read axis data fails\n");
 		goto exit;
 	}
 	meas_reg = ret;

 	mutex_unlock(&data->lock);

 	/* Endian conversion of the measured values. */
 	raw = (s16) (le16_to_cpu(meas_reg));

 	/* Clamp to valid range. */
 	raw = clamp_t(s16, raw, -4096, 4095);
 	*val = raw;
 	return IIO_VAL_INT;

 exit:
 	mutex_unlock(&data->lock);
 	return ret;
 }

 static int ak8975_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan,
 			   int *val, int *val2,
 			   long mask)
 {
 	struct ak8975_data *data = iio_priv(indio_dev);

 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
 		return ak8975_read_axis(indio_dev, chan->address, val);
 	case IIO_CHAN_INFO_SCALE:
 		*val = data->raw_to_gauss[chan->address];
 		return IIO_VAL_INT;
 	}
 	return -EINVAL;
 }

 #define AK8975_CHANNEL(axis, index)					\
 	{								\
 		.type = IIO_MAGN,					\
 		.modified = 1,						\
 		.channel2 = IIO_MOD_##axis,				\
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |		\
 			     BIT(IIO_CHAN_INFO_SCALE),			\
 		.address = index,					\
 	}

 static const struct iio_chan_spec ak8975_channels[] = {
 	AK8975_CHANNEL(X, 0), AK8975_CHANNEL(Y, 1), AK8975_CHANNEL(Z, 2),
 };

 static const struct iio_info ak8975_info = {
 	.read_raw = &ak8975_read_raw,
 	.driver_module = THIS_MODULE,
 };

 static int ak8975_probe(struct i2c_client *client,
 			const struct i2c_device_id *id)
 {
 	struct ak8975_data *data;
 	struct iio_dev *indio_dev;
 	int eoc_gpio;
 	int err;

 	/* Grab and set up the supplied GPIO. */
 	if (client->dev.platform_data == NULL)
 		eoc_gpio = -1;
 	else
 		eoc_gpio = *(int *)(client->dev.platform_data);

 	/* We may not have a GPIO based IRQ to scan, that is fine, we will
 	   poll if so */
 	if (gpio_is_valid(eoc_gpio)) {
 		err = gpio_request_one(eoc_gpio, GPIOF_IN, "ak_8975");
 		if (err < 0) {
 			dev_err(&client->dev,
 				"failed to request GPIO %d, error %d\n",
 							eoc_gpio, err);
 			goto exit;
 		}
 	}

 	/* Register with IIO */
 	indio_dev = iio_device_alloc(sizeof(*data));
 	if (indio_dev == NULL) {
 		err = -ENOMEM;
 		goto exit_gpio;
 	}
 	data = iio_priv(indio_dev);
 	i2c_set_clientdata(client, indio_dev);
 	/* Perform some basic start-of-day setup of the device. */
 	err = ak8975_setup(client);
 	if (err < 0) {
 		dev_err(&client->dev, "AK8975 initialization fails\n");
 		goto exit_free_iio;
 	}

 	data->client = client;
 	mutex_init(&data->lock);
 	data->eoc_gpio = eoc_gpio;
 	indio_dev->dev.parent = &client->dev;
 	indio_dev->channels = ak8975_channels;
 	indio_dev->num_channels = ARRAY_SIZE(ak8975_channels);
 	indio_dev->info = &ak8975_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;

 	err = iio_device_register(indio_dev);
 	if (err < 0)
 		goto exit_free_iio;

 	return 0;

 exit_free_iio:
 	iio_device_free(indio_dev);
 exit_gpio:
 	if (gpio_is_valid(eoc_gpio))
 		gpio_free(eoc_gpio);
 exit:
 	return err;
 }

 static int ak8975_remove(struct i2c_client *client)
 {
 	struct iio_dev *indio_dev = i2c_get_clientdata(client);
 	struct ak8975_data *data = iio_priv(indio_dev);

 	iio_device_unregister(indio_dev);

 	if (gpio_is_valid(data->eoc_gpio))
 		gpio_free(data->eoc_gpio);

 	iio_device_free(indio_dev);

 	return 0;
 }

 static const struct i2c_device_id ak8975_id[] = {
 	{"ak8975", 0},
 	{}
 };

 MODULE_DEVICE_TABLE(i2c, ak8975_id);

 static const struct of_device_id ak8975_of_match[] = {
 	{ .compatible = "asahi-kasei,ak8975", },
 	{ .compatible = "ak8975", },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, ak8975_of_match);

 static struct i2c_driver ak8975_driver = {
 	.driver = {
 		.name	= "ak8975",
 		.of_match_table = ak8975_of_match,
 	},
 	.probe		= ak8975_probe,
 	.remove		= ak8975_remove,
 	.id_table	= ak8975_id,
 };
 module_i2c_driver(ak8975_driver);

 MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
 MODULE_DESCRIPTION("AK8975 magnetometer driver");
 MODULE_LICENSE("GPL");
	/*
	* A sensor driver for the magnetometer AK8975.
	*
	* Magnetic compass sensor driver for monitoring magnetic flux information.
	*
	* Copyright (c) 2010, NVIDIA Corporation.
	*
	* 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.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	*/

	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/i2c.h>
	#include <linux/err.h>
	#include <linux/mutex.h>
	#include <linux/delay.h>

	#include <linux/gpio.h>

	#include <linux/iio/iio.h>
	#include <linux/iio/sysfs.h>
	/*
	* Register definitions, as well as various shifts and masks to get at the
	* individual fields of the registers.
	*/
	#define AK8975_REG_WIA 0x00
	#define AK8975_DEVICE_ID 0x48

	#define AK8975_REG_INFO 0x01

	#define AK8975_REG_ST1 0x02
	#define AK8975_REG_ST1_DRDY_SHIFT 0
	#define AK8975_REG_ST1_DRDY_MASK (1 << AK8975_REG_ST1_DRDY_SHIFT)

	#define AK8975_REG_HXL 0x03
	#define AK8975_REG_HXH 0x04
	#define AK8975_REG_HYL 0x05
	#define AK8975_REG_HYH 0x06
	#define AK8975_REG_HZL 0x07
	#define AK8975_REG_HZH 0x08
	#define AK8975_REG_ST2 0x09
	#define AK8975_REG_ST2_DERR_SHIFT 2
	#define AK8975_REG_ST2_DERR_MASK (1 << AK8975_REG_ST2_DERR_SHIFT)

	#define AK8975_REG_ST2_HOFL_SHIFT 3
	#define AK8975_REG_ST2_HOFL_MASK (1 << AK8975_REG_ST2_HOFL_SHIFT)

	#define AK8975_REG_CNTL 0x0A
	#define AK8975_REG_CNTL_MODE_SHIFT 0
	#define AK8975_REG_CNTL_MODE_MASK (0xF << AK8975_REG_CNTL_MODE_SHIFT)
	#define AK8975_REG_CNTL_MODE_POWER_DOWN 0
	#define AK8975_REG_CNTL_MODE_ONCE 1
	#define AK8975_REG_CNTL_MODE_SELF_TEST 8
	#define AK8975_REG_CNTL_MODE_FUSE_ROM 0xF

	#define AK8975_REG_RSVC 0x0B
	#define AK8975_REG_ASTC 0x0C
	#define AK8975_REG_TS1 0x0D
	#define AK8975_REG_TS2 0x0E
	#define AK8975_REG_I2CDIS 0x0F
	#define AK8975_REG_ASAX 0x10
	#define AK8975_REG_ASAY 0x11
	#define AK8975_REG_ASAZ 0x12

	#define AK8975_MAX_REGS AK8975_REG_ASAZ

	/*
	* Miscellaneous values.
	*/
	#define AK8975_MAX_CONVERSION_TIMEOUT 500
	#define AK8975_CONVERSION_DONE_POLL_TIME 10

	/*
	* Per-instance context data for the device.
	*/
	struct ak8975_data {
	struct i2c_client *client;
	struct attribute_group attrs;
	struct mutex lock;
	u8 asa[3];
	long raw_to_gauss[3];
	u8 reg_cache[AK8975_MAX_REGS];
	int eoc_gpio;
	};

	static const int ak8975_index_to_reg[] = {
	AK8975_REG_HXL, AK8975_REG_HYL, AK8975_REG_HZL,
	};

	/*
	* Helper function to write to the I2C device's registers.
	*/
	static int ak8975_write_data(struct i2c_client *client,
	u8 reg, u8 val, u8 mask, u8 shift)
	{
	struct iio_dev *indio_dev = i2c_get_clientdata(client);
	struct ak8975_data *data = iio_priv(indio_dev);
	u8 regval;
	int ret;

	regval = (data->reg_cache[reg] & ~mask) \| (val << shift);
	ret = i2c_smbus_write_byte_data(client, reg, regval);
	if (ret < 0) {
	dev_err(&client->dev, "Write to device fails status %x\n", ret);
	return ret;
	}
	data->reg_cache[reg] = regval;

	return 0;
	}

	/*
	* Perform some start-of-day setup, including reading the asa calibration
	* values and caching them.
	*/
	static int ak8975_setup(struct i2c_client *client)
	{
	struct iio_dev *indio_dev = i2c_get_clientdata(client);
	struct ak8975_data *data = iio_priv(indio_dev);
	u8 device_id;
	int ret;

	/* Confirm that the device we're talking to is really an AK8975. */
	ret = i2c_smbus_read_byte_data(client, AK8975_REG_WIA);
	if (ret < 0) {
	dev_err(&client->dev, "Error reading WIA\n");
	return ret;
	}
	device_id = ret;
	if (device_id != AK8975_DEVICE_ID) {
	dev_err(&client->dev, "Device ak8975 not found\n");
	return -ENODEV;
	}

	/* Write the fused rom access mode. */
	ret = ak8975_write_data(client,
	AK8975_REG_CNTL,
	AK8975_REG_CNTL_MODE_FUSE_ROM,
	AK8975_REG_CNTL_MODE_MASK,
	AK8975_REG_CNTL_MODE_SHIFT);
	if (ret < 0) {
	dev_err(&client->dev, "Error in setting fuse access mode\n");
	return ret;
	}

	/* Get asa data and store in the device data. */
	ret = i2c_smbus_read_i2c_block_data(client, AK8975_REG_ASAX,
	3, data->asa);
	if (ret < 0) {
	dev_err(&client->dev, "Not able to read asa data\n");
	return ret;
	}

	/* After reading fuse ROM data set power-down mode */
	ret = ak8975_write_data(client,
	AK8975_REG_CNTL,
	AK8975_REG_CNTL_MODE_POWER_DOWN,
	AK8975_REG_CNTL_MODE_MASK,
	AK8975_REG_CNTL_MODE_SHIFT);
	if (ret < 0) {
	dev_err(&client->dev, "Error in setting power-down mode\n");
	return ret;
	}

	/*
	* Precalculate scale factor (in Gauss units) for each axis and
	* store in the device data.
	*
	* This scale factor is axis-dependent, and is derived from 3 calibration
	* factors ASA(x), ASA(y), and ASA(z).
	*
	* These ASA values are read from the sensor device at start of day, and
	* cached in the device context struct.
	*
	* Adjusting the flux value with the sensitivity adjustment value should be
	* done via the following formula:
	*
	* Hadj = H * ( ( ( (ASA-128)*0.5 ) / 128 ) + 1 )
	*
	* where H is the raw value, ASA is the sensitivity adjustment, and Hadj
	* is the resultant adjusted value.
	*
	* We reduce the formula to:
	*
	* Hadj = H * (ASA + 128) / 256
	*
	* H is in the range of -4096 to 4095. The magnetometer has a range of
	* +-1229uT. To go from the raw value to uT is:
	*
	* HuT = H * 1229/4096, or roughly, 3/10.
	*
	* Since 1uT = 100 gauss, our final scale factor becomes:
	*
	* Hadj = H * ((ASA + 128) / 256) * 3/10 * 100
	* Hadj = H * ((ASA + 128) * 30 / 256
	*
	* Since ASA doesn't change, we cache the resultant scale factor into the
	* device context in ak8975_setup().
	*/
	data->raw_to_gauss[0] = ((data->asa[0] + 128) * 30) >> 8;
	data->raw_to_gauss[1] = ((data->asa[1] + 128) * 30) >> 8;
	data->raw_to_gauss[2] = ((data->asa[2] + 128) * 30) >> 8;

	return 0;
	}

	static int wait_conversion_complete_gpio(struct ak8975_data *data)
	{
	struct i2c_client *client = data->client;
	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
	int ret;

	/* Wait for the conversion to complete. */
	while (timeout_ms) {
	msleep(AK8975_CONVERSION_DONE_POLL_TIME);
	if (gpio_get_value(data->eoc_gpio))
	break;
	timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
	}
	if (!timeout_ms) {
	dev_err(&client->dev, "Conversion timeout happened\n");
	return -EINVAL;
	}

	ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST1);
	if (ret < 0)
	dev_err(&client->dev, "Error in reading ST1\n");

	return ret;
	}

	static int wait_conversion_complete_polled(struct ak8975_data *data)
	{
	struct i2c_client *client = data->client;
	u8 read_status;
	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
	int ret;

	/* Wait for the conversion to complete. */
	while (timeout_ms) {
	msleep(AK8975_CONVERSION_DONE_POLL_TIME);
	ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST1);
	if (ret < 0) {
	dev_err(&client->dev, "Error in reading ST1\n");
	return ret;
	}
	read_status = ret;
	if (read_status)
	break;
	timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
	}
	if (!timeout_ms) {
	dev_err(&client->dev, "Conversion timeout happened\n");
	return -EINVAL;
	}
	return read_status;
	}

	/*
	* Emits the raw flux value for the x, y, or z axis.
	*/
	static int ak8975_read_axis(struct iio_dev indio_dev, int index, int val)
	{
	struct ak8975_data *data = iio_priv(indio_dev);
	struct i2c_client *client = data->client;
	u16 meas_reg;
	s16 raw;
	int ret;

	mutex_lock(&data->lock);

	/* Set up the device for taking a sample. */
	ret = ak8975_write_data(client,
	AK8975_REG_CNTL,
	AK8975_REG_CNTL_MODE_ONCE,
	AK8975_REG_CNTL_MODE_MASK,
	AK8975_REG_CNTL_MODE_SHIFT);
	if (ret < 0) {
	dev_err(&client->dev, "Error in setting operating mode\n");
	goto exit;
	}

	/* Wait for the conversion to complete. */
	if (gpio_is_valid(data->eoc_gpio))
	ret = wait_conversion_complete_gpio(data);
	else
	ret = wait_conversion_complete_polled(data);
	if (ret < 0)
	goto exit;

	if (ret & AK8975_REG_ST1_DRDY_MASK) {
	ret = i2c_smbus_read_byte_data(client, AK8975_REG_ST2);
	if (ret < 0) {
	dev_err(&client->dev, "Error in reading ST2\n");
	goto exit;
	}
	if (ret & (AK8975_REG_ST2_DERR_MASK \|
	AK8975_REG_ST2_HOFL_MASK)) {
	dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
	ret = -EINVAL;
	goto exit;
	}
	}

	/* Read the flux value from the appropriate register
	(the register is specified in the iio device attributes). */
	ret = i2c_smbus_read_word_data(client, ak8975_index_to_reg[index]);
	if (ret < 0) {
	dev_err(&client->dev, "Read axis data fails\n");
	goto exit;
	}
	meas_reg = ret;

	mutex_unlock(&data->lock);

	/* Endian conversion of the measured values. */
	raw = (s16) (le16_to_cpu(meas_reg));

	/* Clamp to valid range. */
	raw = clamp_t(s16, raw, -4096, 4095);
	*val = raw;
	return IIO_VAL_INT;

	exit:
	mutex_unlock(&data->lock);
	return ret;
	}

	static int ak8975_read_raw(struct iio_dev *indio_dev,
	struct iio_chan_spec const *chan,
	int val, int val2,
	long mask)
	{
	struct ak8975_data *data = iio_priv(indio_dev);

	switch (mask) {
	case IIO_CHAN_INFO_RAW:
	return ak8975_read_axis(indio_dev, chan->address, val);
	case IIO_CHAN_INFO_SCALE:
	*val = data->raw_to_gauss[chan->address];
	return IIO_VAL_INT;
	}
	return -EINVAL;
	}

	#define AK8975_CHANNEL(axis, index) \
	{ \
	.type = IIO_MAGN, \
	.modified = 1, \
	.channel2 = IIO_MOD_##axis, \
	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) \| \
	BIT(IIO_CHAN_INFO_SCALE), \
	.address = index, \
	}

	static const struct iio_chan_spec ak8975_channels[] = {
	AK8975_CHANNEL(X, 0), AK8975_CHANNEL(Y, 1), AK8975_CHANNEL(Z, 2),
	};

	static const struct iio_info ak8975_info = {
	.read_raw = &ak8975_read_raw,
	.driver_module = THIS_MODULE,
	};

	static int ak8975_probe(struct i2c_client *client,
	const struct i2c_device_id *id)
	{
	struct ak8975_data *data;
	struct iio_dev *indio_dev;
	int eoc_gpio;
	int err;

	/* Grab and set up the supplied GPIO. */
	if (client->dev.platform_data == NULL)
	eoc_gpio = -1;
	else
	eoc_gpio = (int )(client->dev.platform_data);

	/* We may not have a GPIO based IRQ to scan, that is fine, we will
	poll if so */
	if (gpio_is_valid(eoc_gpio)) {
	err = gpio_request_one(eoc_gpio, GPIOF_IN, "ak_8975");
	if (err < 0) {
	dev_err(&client->dev,
	"failed to request GPIO %d, error %d\n",
	eoc_gpio, err);
	goto exit;
	}
	}

	/* Register with IIO */
	indio_dev = iio_device_alloc(sizeof(*data));
	if (indio_dev == NULL) {
	err = -ENOMEM;
	goto exit_gpio;
	}
	data = iio_priv(indio_dev);
	i2c_set_clientdata(client, indio_dev);
	/* Perform some basic start-of-day setup of the device. */
	err = ak8975_setup(client);
	if (err < 0) {
	dev_err(&client->dev, "AK8975 initialization fails\n");
	goto exit_free_iio;
	}

	data->client = client;
	mutex_init(&data->lock);
	data->eoc_gpio = eoc_gpio;
	indio_dev->dev.parent = &client->dev;
	indio_dev->channels = ak8975_channels;
	indio_dev->num_channels = ARRAY_SIZE(ak8975_channels);
	indio_dev->info = &ak8975_info;
	indio_dev->modes = INDIO_DIRECT_MODE;

	err = iio_device_register(indio_dev);
	if (err < 0)
	goto exit_free_iio;

	return 0;

	exit_free_iio:
	iio_device_free(indio_dev);
	exit_gpio:
	if (gpio_is_valid(eoc_gpio))
	gpio_free(eoc_gpio);
	exit:
	return err;
	}

	static int ak8975_remove(struct i2c_client *client)
	{
	struct iio_dev *indio_dev = i2c_get_clientdata(client);
	struct ak8975_data *data = iio_priv(indio_dev);

	iio_device_unregister(indio_dev);

	if (gpio_is_valid(data->eoc_gpio))
	gpio_free(data->eoc_gpio);

	iio_device_free(indio_dev);

	return 0;
	}

	static const struct i2c_device_id ak8975_id[] = {
	{"ak8975", 0},
	{}
	};

	MODULE_DEVICE_TABLE(i2c, ak8975_id);

	static const struct of_device_id ak8975_of_match[] = {
	{ .compatible = "asahi-kasei,ak8975", },
	{ .compatible = "ak8975", },
	{ }
	};
	MODULE_DEVICE_TABLE(of, ak8975_of_match);

	static struct i2c_driver ak8975_driver = {
	.driver = {
	.name = "ak8975",
	.of_match_table = ak8975_of_match,
	},
	.probe = ak8975_probe,
	.remove = ak8975_remove,
	.id_table = ak8975_id,
	};
	module_i2c_driver(ak8975_driver);

	MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
	MODULE_DESCRIPTION("AK8975 magnetometer driver");
	MODULE_LICENSE("GPL");