/*
 * 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 "../iio.h"
#include "magnet.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 iio_dev		*indio_dev;
	struct attribute_group	attrs;
	struct mutex		lock;
	u8			asa[3];
	long			raw_to_gauss[3];
	unsigned long		mode;
	u8			reg_cache[AK8975_MAX_REGS];
	int			eoc_gpio;
	int			eoc_irq;
};

/*
 * 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)
{
	u8 regval;
	struct i2c_msg msg;
	u8 w_data[2];
	int ret = 0;

	struct ak8975_data *data = i2c_get_clientdata(client);

	regval = data->reg_cache[reg];
	regval &= ~mask;
	regval |= val << shift;

	w_data[0] = reg;
	w_data[1] = regval;

	msg.addr = client->addr;
	msg.flags = 0;
	msg.len = 2;
	msg.buf = w_data;

	ret = i2c_transfer(client->adapter, &msg, 1);
	if (ret < 0) {
		dev_err(&client->dev, "Write to device fails status %x\n", ret);
		return ret;
	}
	data->reg_cache[reg] = regval;

	return 0;
}

/*
 * Helper function to read a contiguous set of the I2C device's registers.
 */
static int ak8975_read_data(struct i2c_client *client,
			    u8 reg, u8 length, u8 *buffer)
{
	struct i2c_msg msg[2];
	u8 w_data[2];
	int ret;

	w_data[0] = reg;

	msg[0].addr = client->addr;
	msg[0].flags = I2C_M_NOSTART;	/* set repeated start and write */
	msg[0].len = 1;
	msg[0].buf = w_data;

	msg[1].addr = client->addr;
	msg[1].flags = I2C_M_RD;
	msg[1].len = length;
	msg[1].buf = buffer;

	ret = i2c_transfer(client->adapter, msg, 2);
	if (ret < 0) {
		dev_err(&client->dev, "Read from device fails\n");
		return ret;
	}

	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 ak8975_data *data = i2c_get_clientdata(client);
	u8 device_id;
	int ret;

	/* Confirm that the device we're talking to is really an AK8975. */
	ret = ak8975_read_data(client, AK8975_REG_WIA, 1, &device_id);
	if (ret < 0) {
		dev_err(&client->dev, "Error reading WIA\n");
		return 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 = ak8975_read_data(client, AK8975_REG_ASAX, 3, data->asa);
	if (ret < 0) {
		dev_err(&client->dev, "Not able to read asa data\n");
		return ret;
	}

	/* Precalculate scale factor for each axis and
           store in the device data. */
	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;
}

/*
 * Shows the device's mode.  0 = off, 1 = on.
 */
static ssize_t show_mode(struct device *dev, struct device_attribute *devattr,
			 char *buf)
{
	struct iio_dev *indio_dev = dev_get_drvdata(dev);
	struct ak8975_data *data = indio_dev->dev_data;

	return sprintf(buf, "%lu\n", data->mode);
}

/*
 * Sets the device's mode.  0 = off, 1 = on.  The device's mode must be on
 * for the magn raw attributes to be available.
 */
static ssize_t store_mode(struct device *dev, struct device_attribute *devattr,
			  const char *buf, size_t count)
{
	struct iio_dev *indio_dev = dev_get_drvdata(dev);
	struct ak8975_data *data = indio_dev->dev_data;
	struct i2c_client *client = data->client;
	unsigned long oval;
	int ret;

	/* Convert mode string and do some basic sanity checking on it.
	   only 0 or 1 are valid. */
	if (strict_strtoul(buf, 10, &oval))
		return -EINVAL;

	if (oval > 1) {
		dev_err(dev, "mode value is not supported\n");
		return -EINVAL;
	}

	mutex_lock(&data->lock);

	/* Write the mode to the device. */
	if (data->mode != oval) {
		ret = ak8975_write_data(client,
					AK8975_REG_CNTL,
					(u8)oval,
					AK8975_REG_CNTL_MODE_MASK,
					AK8975_REG_CNTL_MODE_SHIFT);

		if (ret < 0) {
			dev_err(&client->dev, "Error in setting mode\n");
			mutex_unlock(&data->lock);
			return ret;
		}
		data->mode = oval;
	}

	mutex_unlock(&data->lock);

	return count;
}

/*
 * Emits the scale factor to bring the raw value into Gauss units.
 *
 * 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().
 */
static ssize_t show_scale(struct device *dev, struct device_attribute *devattr,
			  char *buf)
{
	struct iio_dev *indio_dev = dev_get_drvdata(dev);
	struct ak8975_data *data = indio_dev->dev_data;
	struct iio_dev_attr *this_attr = to_iio_dev_attr(devattr);

	return sprintf(buf, "%ld\n", data->raw_to_gauss[this_attr->address]);
}

/*
 * Emits the raw flux value for the x, y, or z axis.
 */
static ssize_t show_raw(struct device *dev, struct device_attribute *devattr,
			char *buf)
{
	struct iio_dev *indio_dev = dev_get_drvdata(dev);
	struct ak8975_data *data = indio_dev->dev_data;
	struct i2c_client *client = data->client;
	struct iio_dev_attr *this_attr = to_iio_dev_attr(devattr);
	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
	u16 meas_reg;
	s16 raw;
	u8 read_status;
	int ret;

	mutex_lock(&data->lock);

	if (data->mode == 0) {
		dev_err(&client->dev, "Operating mode is in power down mode\n");
		ret = -EBUSY;
		goto exit;
	}

	/* 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. */
	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");
		ret = -EINVAL;
		goto exit;
	}

	ret = ak8975_read_data(client, AK8975_REG_ST1, 1, &read_status);
	if (ret < 0) {
		dev_err(&client->dev, "Error in reading ST1\n");
		goto exit;
	}

	if (read_status & AK8975_REG_ST1_DRDY_MASK) {
		ret = ak8975_read_data(client, AK8975_REG_ST2, 1, &read_status);
		if (ret < 0) {
			dev_err(&client->dev, "Error in reading ST2\n");
			goto exit;
		}
		if (read_status & (AK8975_REG_ST2_DERR_MASK |
				   AK8975_REG_ST2_HOFL_MASK)) {
			dev_err(&client->dev, "ST2 status error 0x%x\n",
				read_status);
			ret = -EINVAL;
			goto exit;
		}
	}

	/* Read the flux value from the appropriate register
	   (the register is specified in the iio device attributes). */
	ret = ak8975_read_data(client, this_attr->address, 2, (u8 *)&meas_reg);
	if (ret < 0) {
		dev_err(&client->dev, "Read axis data fails\n");
		goto exit;
	}

	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);

	return sprintf(buf, "%d\n", raw);

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

static IIO_DEVICE_ATTR(mode, S_IRUGO | S_IWUSR, show_mode, store_mode, 0);
static IIO_DEV_ATTR_MAGN_X_SCALE(S_IRUGO, show_scale, NULL, 0);
static IIO_DEV_ATTR_MAGN_Y_SCALE(S_IRUGO, show_scale, NULL, 1);
static IIO_DEV_ATTR_MAGN_Z_SCALE(S_IRUGO, show_scale, NULL, 2);
static IIO_DEV_ATTR_MAGN_X(show_raw, AK8975_REG_HXL);
static IIO_DEV_ATTR_MAGN_Y(show_raw, AK8975_REG_HYL);
static IIO_DEV_ATTR_MAGN_Z(show_raw, AK8975_REG_HZL);

static struct attribute *ak8975_attr[] = {
	&iio_dev_attr_mode.dev_attr.attr,
	&iio_dev_attr_magn_x_scale.dev_attr.attr,
	&iio_dev_attr_magn_y_scale.dev_attr.attr,
	&iio_dev_attr_magn_z_scale.dev_attr.attr,
	&iio_dev_attr_magn_x_raw.dev_attr.attr,
	&iio_dev_attr_magn_y_raw.dev_attr.attr,
	&iio_dev_attr_magn_z_raw.dev_attr.attr,
	NULL
};

static struct attribute_group ak8975_attr_group = {
	.attrs = ak8975_attr,
};

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

	/* Allocate our device context. */
	data = kzalloc(sizeof(struct ak8975_data), GFP_KERNEL);
	if (!data) {
		dev_err(&client->dev, "Memory allocation fails\n");
		err = -ENOMEM;
		goto exit;
	}

	i2c_set_clientdata(client, data);
	data->client = client;

	mutex_init(&data->lock);

	/* Grab and set up the supplied GPIO. */
	data->eoc_irq = client->irq;
	data->eoc_gpio = irq_to_gpio(client->irq);

	if (!data->eoc_gpio) {
		dev_err(&client->dev, "failed, no valid GPIO\n");
		err = -EINVAL;
		goto exit_free;
	}

	err = gpio_request(data->eoc_gpio, "ak_8975");
	if (err < 0) {
		dev_err(&client->dev, "failed to request GPIO %d, error %d\n",
			data->eoc_gpio, err);
		goto exit_free;
	}

	err = gpio_direction_input(data->eoc_gpio);
	if (err < 0) {
		dev_err(&client->dev, "Failed to configure input direction for"
			" GPIO %d, error %d\n", data->eoc_gpio, err);
		goto exit_gpio;
	}

	/* 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_gpio;
	}

	/* Register with IIO */
	data->indio_dev = iio_allocate_device();
	if (data->indio_dev == NULL) {
		err = -ENOMEM;
		goto exit_gpio;
	}

	data->indio_dev->dev.parent = &client->dev;
	data->indio_dev->attrs = &ak8975_attr_group;
	data->indio_dev->dev_data = (void *)(data);
	data->indio_dev->driver_module = THIS_MODULE;
	data->indio_dev->modes = INDIO_DIRECT_MODE;

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

	return 0;

exit_free_iio:
	iio_free_device(data->indio_dev);
exit_gpio:
	gpio_free(data->eoc_gpio);
exit_free:
	kfree(data);
exit:
	return err;
}

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

	iio_device_unregister(data->indio_dev);
	iio_free_device(data->indio_dev);

	gpio_free(data->eoc_gpio);

	kfree(data);

	return 0;
}

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

MODULE_DEVICE_TABLE(i2c, ak8975_id);

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

static int __init ak8975_init(void)
{
	return i2c_add_driver(&ak8975_driver);
}

static void __exit ak8975_exit(void)
{
	i2c_del_driver(&ak8975_driver);
}

module_init(ak8975_init);
module_exit(ak8975_exit);

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