staging: iio: ak8975: Add ak8975 magnetometer sensor

This is for the Asahi Kasei AK8975 3-axis magnetometer.  It resides within
the magnetometer section of the IIO subsystem, and implements the raw
magn_x,y,z_raw attributes, as well as magn_x,y,z_scale attributes for
converting to Gauss.

Changed to use the magn_x,y,z_scale attributes, and made those attributes
give the scale factor to conert to Gauss.  Also applied more fixes from
feedback.

Keeping mode as an unsigned long.  I'm going to add proper power management
at some point anyway, which would deprecate this attribute.

Signed-off-by: Andrew Chew <achew@nvidia.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/magnetometer/Kconfig

@@ -3,6 +3,16 @@
 #
 comment "Magnetometer sensors"
 
+config SENSORS_AK8975
+	tristate "Asahi Kasei AK8975 3-Axis Magnetometer"
+	depends on I2C
+	help
+	  Say yes here to build support for Asahi Kasei AK8975 3-Axis
+	  Magnetometer.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ak8975.
+
 config SENSORS_HMC5843
 	tristate "Honeywell HMC5843 3-Axis Magnetometer"
 	depends on I2C

drivers/staging/iio/magnetometer/Makefile

@@ -2,4 +2,5 @@
 # Makefile for industrial I/O Magnetometer sensors
 #
 
+obj-$(CONFIG_SENSORS_AK8975)	+= ak8975.o
 obj-$(CONFIG_SENSORS_HMC5843)	+= hmc5843.o

drivers/staging/iio/magnetometer/ak8975.c

@@ -0,0 +1,558 @@
+/*
+ * 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");