drivers/misc: support for the pressure sensor BMP085 from Bosch Sensortec

This driver adds support for the BMP085 digital pressure sensor from Bosch
Sensortec.  It exposes a sysfs api to userspace where pressure and
temperature measurement results can be read from the pressure0_input and
temp0_input file.  The chip is able to calculate the average of up to
eight samples to increase the accuracy.  This feature can be controlled by
writing to the oversampling file.

The BMP085 digital pressure sensor can measure ambient air pressure and
temperature.  Both values can be obtained from sysfs files.  The pressure
is measured by reading from pressure0_input.  Valid values range from
30000 to 110000 pascal with a resolution of 1 pascal (=0.01 millibar).

temp0_input holds the current temperature in degree celsius, multiplied by
10.  This results in a resolution of a tenth degree celsius.  Values range
from -400 to 850.

To increase the accuracy, this chip can calculate the average of 1, 2, 4
or 8 samples.  This behavior is controlled through the oversampling sysfs
file.  Two to the power of the value written to that file specifies how
many samples will be used.  Valid values: 0..3.

[akpm@linux-foundation.org: fix typo]
[shubhrajyoti@ti.com: optimize the wait time for the pressure sensor, definition of long is arch dependent so make it u32]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Christoph Mair <christoph.mair@gmail.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Stefan Schmidt <stefan@datenfreihafen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/ABI/testing/sysfs-i2c-bmp085

@@ -0,0 +1,31 @@
+What:		/sys/bus/i2c/devices/<busnum>-<devaddr>/pressure0_input
+Date:		June 2010
+Contact:	Christoph Mair <christoph.mair@gmail.com>
+Description:	Start a pressure measurement and read the result. Values
+		represent the ambient air pressure in pascal (0.01 millibar).
+
+		Reading: returns the current air pressure.
+
+
+What:		/sys/bus/i2c/devices/<busnum>-<devaddr>/temp0_input
+Date:		June 2010
+Contact:	Christoph Mair <christoph.mair@gmail.com>
+Description:	Measure the ambient temperature. The returned value represents
+		the ambient temperature in units of 0.1 degree celsius.
+
+		Reading: returns the current temperature.
+
+
+What:		/sys/bus/i2c/devices/<busnum>-<devaddr>/oversampling
+Date:		June 2010
+Contact:	Christoph Mair <christoph.mair@gmail.com>
+Description:	Tell the bmp085 to use more samples to calculate a pressure
+		value. When writing to this file the chip will use 2^x samples
+		to calculate the next pressure value with x being the value
+		written. Using this feature will decrease RMS noise and
+		increase the measurement time.
+
+		Reading: returns the current oversampling setting.
+
+		Writing: sets a new oversampling setting.
+		Accepted values: 0..3.

drivers/misc/Kconfig

@@ -373,6 +373,16 @@ config ARM_CHARLCD
 	  line and the Linux version on the second line, but that's
 	  still useful.
 
+config BMP085
+	tristate "BMP085 digital pressure sensor"
+	depends on I2C && SYSFS
+	help
+	  If you say yes here you get support for the Bosch Sensortec
+	  BMP086 digital pressure sensor.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called bmp085.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"

drivers/misc/Makefile

@@ -9,6 +9,7 @@ obj-$(CONFIG_AD525X_DPOT_SPI)	+= ad525x_dpot-spi.o
 obj-$(CONFIG_ATMEL_PWM)		+= atmel_pwm.o
 obj-$(CONFIG_ATMEL_SSC)		+= atmel-ssc.o
 obj-$(CONFIG_ATMEL_TCLIB)	+= atmel_tclib.o
+obj-$(CONFIG_BMP085)		+= bmp085.o
 obj-$(CONFIG_ICS932S401)	+= ics932s401.o
 obj-$(CONFIG_LKDTM)		+= lkdtm.o
 obj-$(CONFIG_TIFM_CORE)       	+= tifm_core.o

drivers/misc/bmp085.c

@@ -0,0 +1,482 @@
+/*  Copyright (c) 2010  Christoph Mair <christoph.mair@gmail.com>
+
+    This driver supports the bmp085 digital barometric pressure
+    and temperature sensor from Bosch Sensortec. The datasheet
+    is avaliable from their website:
+    http://www.bosch-sensortec.com/content/language1/downloads/BST-BMP085-DS000-05.pdf
+
+    A pressure measurement is issued by reading from pressure0_input.
+    The return value ranges from 30000 to 110000 pascal with a resulution
+    of 1 pascal (0.01 millibar) which enables measurements from 9000m above
+    to 500m below sea level.
+
+    The temperature can be read from temp0_input. Values range from
+    -400 to 850 representing the ambient temperature in degree celsius
+    multiplied by 10.The resolution is 0.1 celsius.
+
+    Because ambient pressure is temperature dependent, a temperature
+    measurement will be executed automatically even if the user is reading
+    from pressure0_input. This happens if the last temperature measurement
+    has been executed more then one second ago.
+
+    To decrease RMS noise from pressure measurements, the bmp085 can
+    autonomously calculate the average of up to eight samples. This is
+    set up by writing to the oversampling sysfs file. Accepted values
+    are 0, 1, 2 and 3. 2^x when x is the value written to this file
+    specifies the number of samples used to calculate the ambient pressure.
+    RMS noise is specified with six pascal (without averaging) and decreases
+    down to 3 pascal when using an oversampling setting of 3.
+
+    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/module.h>
+#include <linux/init.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/delay.h>
+
+
+#define BMP085_I2C_ADDRESS		0x77
+#define BMP085_CHIP_ID			0x55
+
+#define BMP085_CALIBRATION_DATA_START	0xAA
+#define BMP085_CALIBRATION_DATA_LENGTH	11	/* 16 bit values */
+#define BMP085_CHIP_ID_REG		0xD0
+#define BMP085_VERSION_REG		0xD1
+#define BMP085_CTRL_REG			0xF4
+#define BMP085_TEMP_MEASUREMENT		0x2E
+#define BMP085_PRESSURE_MEASUREMENT	0x34
+#define BMP085_CONVERSION_REGISTER_MSB	0xF6
+#define BMP085_CONVERSION_REGISTER_LSB	0xF7
+#define BMP085_CONVERSION_REGISTER_XLSB	0xF8
+#define BMP085_TEMP_CONVERSION_TIME	5
+
+#define BMP085_CLIENT_NAME		"bmp085"
+
+
+static const unsigned short normal_i2c[] = { BMP085_I2C_ADDRESS,
+							I2C_CLIENT_END };
+
+struct bmp085_calibration_data {
+	s16 AC1, AC2, AC3;
+	u16 AC4, AC5, AC6;
+	s16 B1, B2;
+	s16 MB, MC, MD;
+};
+
+
+/* Each client has this additional data */
+struct bmp085_data {
+	struct i2c_client *client;
+	struct mutex lock;
+	struct bmp085_calibration_data calibration;
+	u32 raw_temperature;
+	u32 raw_pressure;
+	unsigned char oversampling_setting;
+	u32 last_temp_measurement;
+	s32 b6; /* calculated temperature correction coefficient */
+};
+
+
+static s32 bmp085_read_calibration_data(struct i2c_client *client)
+{
+	u16 tmp[BMP085_CALIBRATION_DATA_LENGTH];
+	struct bmp085_data *data = i2c_get_clientdata(client);
+	struct bmp085_calibration_data *cali = &(data->calibration);
+	s32 status = i2c_smbus_read_i2c_block_data(client,
+				BMP085_CALIBRATION_DATA_START,
+				BMP085_CALIBRATION_DATA_LENGTH*sizeof(u16),
+				(u8 *)tmp);
+	if (status < 0)
+		return status;
+
+	if (status != BMP085_CALIBRATION_DATA_LENGTH*sizeof(u16))
+		return -EIO;
+
+	cali->AC1 =  be16_to_cpu(tmp[0]);
+	cali->AC2 =  be16_to_cpu(tmp[1]);
+	cali->AC3 =  be16_to_cpu(tmp[2]);
+	cali->AC4 =  be16_to_cpu(tmp[3]);
+	cali->AC5 =  be16_to_cpu(tmp[4]);
+	cali->AC6 = be16_to_cpu(tmp[5]);
+	cali->B1 = be16_to_cpu(tmp[6]);
+	cali->B2 = be16_to_cpu(tmp[7]);
+	cali->MB = be16_to_cpu(tmp[8]);
+	cali->MC = be16_to_cpu(tmp[9]);
+	cali->MD = be16_to_cpu(tmp[10]);
+	return 0;
+}
+
+
+static s32 bmp085_update_raw_temperature(struct bmp085_data *data)
+{
+	u16 tmp;
+	s32 status;
+
+	mutex_lock(&data->lock);
+	status = i2c_smbus_write_byte_data(data->client, BMP085_CTRL_REG,
+						BMP085_TEMP_MEASUREMENT);
+	if (status != 0) {
+		dev_err(&data->client->dev,
+			"Error while requesting temperature measurement.\n");
+		goto exit;
+	}
+	msleep(BMP085_TEMP_CONVERSION_TIME);
+
+	status = i2c_smbus_read_i2c_block_data(data->client,
+		BMP085_CONVERSION_REGISTER_MSB, sizeof(tmp), (u8 *)&tmp);
+	if (status < 0)
+		goto exit;
+	if (status != sizeof(tmp)) {
+		dev_err(&data->client->dev,
+			"Error while reading temperature measurement result\n");
+		status = -EIO;
+		goto exit;
+	}
+	data->raw_temperature = be16_to_cpu(tmp);
+	data->last_temp_measurement = jiffies;
+	status = 0;	/* everything ok, return 0 */
+
+exit:
+	mutex_unlock(&data->lock);
+	return status;
+}
+
+static s32 bmp085_update_raw_pressure(struct bmp085_data *data)
+{
+	u32 tmp = 0;
+	s32 status;
+
+	mutex_lock(&data->lock);
+	status = i2c_smbus_write_byte_data(data->client, BMP085_CTRL_REG,
+		BMP085_PRESSURE_MEASUREMENT + (data->oversampling_setting<<6));
+	if (status != 0) {
+		dev_err(&data->client->dev,
+			"Error while requesting pressure measurement.\n");
+		goto exit;
+	}
+
+	/* wait for the end of conversion */
+	msleep(2+(3 << data->oversampling_setting));
+
+	/* copy data into a u32 (4 bytes), but skip the first byte. */
+	status = i2c_smbus_read_i2c_block_data(data->client,
+			BMP085_CONVERSION_REGISTER_MSB, 3, ((u8 *)&tmp)+1);
+	if (status < 0)
+		goto exit;
+	if (status != 3) {
+		dev_err(&data->client->dev,
+			"Error while reading pressure measurement results\n");
+		status = -EIO;
+		goto exit;
+	}
+	data->raw_pressure = be32_to_cpu((tmp));
+	data->raw_pressure >>= (8-data->oversampling_setting);
+	status = 0;	/* everything ok, return 0 */
+
+exit:
+	mutex_unlock(&data->lock);
+	return status;
+}
+
+
+/*
+ * This function starts the temperature measurement and returns the value
+ * in tenth of a degree celsius.
+ */
+static s32 bmp085_get_temperature(struct bmp085_data *data, int *temperature)
+{
+	struct bmp085_calibration_data *cali = &data->calibration;
+	long x1, x2;
+	int status;
+
+	status = bmp085_update_raw_temperature(data);
+	if (status != 0)
+		goto exit;
+
+	x1 = ((data->raw_temperature - cali->AC6) * cali->AC5) >> 15;
+	x2 = (cali->MC << 11) / (x1 + cali->MD);
+	data->b6 = x1 + x2 - 4000;
+	/* if NULL just update b6. Used for pressure only measurements */
+	if (temperature != NULL)
+		*temperature = (x1+x2+8) >> 4;
+
+exit:
+	return status;;
+}
+
+/*
+ * This function starts the pressure measurement and returns the value
+ * in millibar. Since the pressure depends on the ambient temperature,
+ * a temperature measurement is executed if the last known value is older
+ * than one second.
+ */
+static s32 bmp085_get_pressure(struct bmp085_data *data, int *pressure)
+{
+	struct bmp085_calibration_data *cali = &data->calibration;
+	s32 x1, x2, x3, b3;
+	u32 b4, b7;
+	s32 p;
+	int status;
+
+	/* alt least every second force an update of the ambient temperature */
+	if (data->last_temp_measurement + 1*HZ < jiffies) {
+		status = bmp085_get_temperature(data, NULL);
+		if (status != 0)
+			goto exit;
+	}
+
+	status = bmp085_update_raw_pressure(data);
+	if (status != 0)
+		goto exit;
+
+	x1 = (data->b6 * data->b6) >> 12;
+	x1 *= cali->B2;
+	x1 >>= 11;
+
+	x2 = cali->AC2 * data->b6;
+	x2 >>= 11;
+
+	x3 = x1 + x2;
+
+	b3 = (((((s32)cali->AC1) * 4 + x3) << data->oversampling_setting) + 2);
+	b3 >>= 2;
+
+	x1 = (cali->AC3 * data->b6) >> 13;
+	x2 = (cali->B1 * ((data->b6 * data->b6) >> 12)) >> 16;
+	x3 = (x1 + x2 + 2) >> 2;
+	b4 = (cali->AC4 * (u32)(x3 + 32768)) >> 15;
+
+	b7 = ((u32)data->raw_pressure - b3) *
+					(50000 >> data->oversampling_setting);
+	p = ((b7 < 0x80000000) ? ((b7 << 1) / b4) : ((b7 / b4) * 2));
+
+	x1 = p >> 8;
+	x1 *= x1;
+	x1 = (x1 * 3038) >> 16;
+	x2 = (-7357 * p) >> 16;
+	p += (x1 + x2 + 3791) >> 4;
+
+	*pressure = p;
+
+exit:
+	return status;
+}
+
+/*
+ * This function sets the chip-internal oversampling. Valid values are 0..3.
+ * The chip will use 2^oversampling samples for internal averaging.
+ * This influences the measurement time and the accuracy; larger values
+ * increase both. The datasheet gives on overview on how measurement time,
+ * accuracy and noise correlate.
+ */
+static void bmp085_set_oversampling(struct bmp085_data *data,
+						unsigned char oversampling)
+{
+	if (oversampling > 3)
+		oversampling = 3;
+	data->oversampling_setting = oversampling;
+}
+
+/*
+ * Returns the currently selected oversampling. Range: 0..3
+ */
+static unsigned char bmp085_get_oversampling(struct bmp085_data *data)
+{
+	return data->oversampling_setting;
+}
+
+/* sysfs callbacks */
+static ssize_t set_oversampling(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct bmp085_data *data = i2c_get_clientdata(client);
+	unsigned long oversampling;
+	int success = strict_strtoul(buf, 10, &oversampling);
+	if (success == 0) {
+		bmp085_set_oversampling(data, oversampling);
+		return count;
+	}
+	return success;
+}
+
+static ssize_t show_oversampling(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct bmp085_data *data = i2c_get_clientdata(client);
+	return sprintf(buf, "%u\n", bmp085_get_oversampling(data));
+}
+static DEVICE_ATTR(oversampling, S_IWUSR | S_IRUGO,
+					show_oversampling, set_oversampling);
+
+
+static ssize_t show_temperature(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	int temperature;
+	int status;
+	struct i2c_client *client = to_i2c_client(dev);
+	struct bmp085_data *data = i2c_get_clientdata(client);
+
+	status = bmp085_get_temperature(data, &temperature);
+	if (status != 0)
+		return status;
+	else
+		return sprintf(buf, "%d\n", temperature);
+}
+static DEVICE_ATTR(temp0_input, S_IRUGO, show_temperature, NULL);
+
+
+static ssize_t show_pressure(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	int pressure;
+	int status;
+	struct i2c_client *client = to_i2c_client(dev);
+	struct bmp085_data *data = i2c_get_clientdata(client);
+
+	status = bmp085_get_pressure(data, &pressure);
+	if (status != 0)
+		return status;
+	else
+		return sprintf(buf, "%d\n", pressure);
+}
+static DEVICE_ATTR(pressure0_input, S_IRUGO, show_pressure, NULL);
+
+
+static struct attribute *bmp085_attributes[] = {
+	&dev_attr_temp0_input.attr,
+	&dev_attr_pressure0_input.attr,
+	&dev_attr_oversampling.attr,
+	NULL
+};
+
+static const struct attribute_group bmp085_attr_group = {
+	.attrs = bmp085_attributes,
+};
+
+static int bmp085_detect(struct i2c_client *client, struct i2c_board_info *info)
+{
+	if (client->addr != BMP085_I2C_ADDRESS)
+		return -ENODEV;
+
+	if (i2c_smbus_read_byte_data(client, BMP085_CHIP_ID_REG) != BMP085_CHIP_ID)
+		return -ENODEV;
+
+	return 0;
+}
+
+static int bmp085_init_client(struct i2c_client *client)
+{
+	unsigned char version;
+	int status;
+	struct bmp085_data *data = i2c_get_clientdata(client);
+	data->client = client;
+	status = bmp085_read_calibration_data(client);
+	if (status != 0)
+		goto exit;
+	version = i2c_smbus_read_byte_data(client, BMP085_VERSION_REG);
+	data->last_temp_measurement = 0;
+	data->oversampling_setting = 3;
+	mutex_init(&data->lock);
+	dev_info(&data->client->dev, "BMP085 ver. %d.%d found.\n",
+			(version & 0x0F), (version & 0xF0) >> 4);
+exit:
+	return status;
+}
+
+static int bmp085_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct bmp085_data *data;
+	int err = 0;
+
+	data = kzalloc(sizeof(struct bmp085_data), GFP_KERNEL);
+	if (!data) {
+		err = -ENOMEM;
+		goto exit;
+	}
+
+	/* default settings after POR */
+	data->oversampling_setting = 0x00;
+
+	i2c_set_clientdata(client, data);
+
+	/* Initialize the BMP085 chip */
+	err = bmp085_init_client(client);
+	if (err != 0)
+		goto exit_free;
+
+	/* Register sysfs hooks */
+	err = sysfs_create_group(&client->dev.kobj, &bmp085_attr_group);
+	if (err)
+		goto exit_free;
+
+	dev_info(&data->client->dev, "Succesfully initialized bmp085!\n");
+	goto exit;
+
+exit_free:
+	kfree(data);
+exit:
+	return err;
+}
+
+static int bmp085_remove(struct i2c_client *client)
+{
+	sysfs_remove_group(&client->dev.kobj, &bmp085_attr_group);
+	kfree(i2c_get_clientdata(client));
+	return 0;
+}
+
+static const struct i2c_device_id bmp085_id[] = {
+	{ "bmp085", 0 },
+	{ }
+};
+
+static struct i2c_driver bmp085_driver = {
+	.driver = {
+		.owner = THIS_MODULE,
+		.name	= "bmp085"
+	},
+	.id_table	= bmp085_id,
+	.probe		= bmp085_probe,
+	.remove		= bmp085_remove,
+
+	.detect		= bmp085_detect,
+	.address_list	= normal_i2c
+};
+
+static int __init bmp085_init(void)
+{
+	return i2c_add_driver(&bmp085_driver);
+}
+
+static void __exit bmp085_exit(void)
+{
+	i2c_del_driver(&bmp085_driver);
+}
+
+
+MODULE_AUTHOR("Christoph Mair <christoph.mair@gmail.com");
+MODULE_DESCRIPTION("BMP085 driver");
+MODULE_LICENSE("GPL");
+
+module_init(bmp085_init);
+module_exit(bmp085_exit);