Re: [PATCH] iio: pressure: bmp280: add support for BMP180

[Vlad Dogaru <vlad.dogaru@intel.com>]

On Fri, Apr 08, 2016 at 12:57:01AM +0900, Akinobu Mita wrote:
> This adds support for the BMP180 to the bmp280 iio driver.
> The BMP180 has already been supported by misc/bmp085 driver but it
> doesn't use iio framework.
> 
> This also adds ability to control the oversampling ratio of the
> temperature and pressure measurement for both bmp180 and bmp280.
> (bmp280 is untested)

I think this would be better as two separate patches: one that adds
support for the new chip, and the second which adds the oversampling
ratio.  Once you split these up, I can validate that oversampling works
with the bmp280.

Patch looks good other than that, a couple of questions inline.

> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: Vlad Dogaru <vlad.dogaru@intel.com>
> Cc: Christoph Mair <christoph.mair@gmail.com>
> Cc: Jonathan Cameron <jic23@kernel.org>
> Cc: Hartmut Knaack <knaack.h@gmx.de>
> Cc: Lars-Peter Clausen <lars@metafoo.de>
> Cc: Peter Meerwald <pmeerw@pmeerw.net>
> ---
>  drivers/iio/pressure/Kconfig  |   4 +-
>  drivers/iio/pressure/bmp280.c | 574 +++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 548 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/iio/pressure/Kconfig b/drivers/iio/pressure/Kconfig
> index e8f60db..c9131f8 100644
> --- a/drivers/iio/pressure/Kconfig
> +++ b/drivers/iio/pressure/Kconfig
> @@ -6,11 +6,11 @@
>  menu "Pressure sensors"
>  
>  config BMP280
> -	tristate "Bosch Sensortec BMP280 pressure sensor driver"
> +	tristate "Bosch Sensortec BMP180 and BMP280 pressure sensor driver"
>  	depends on I2C
>  	select REGMAP_I2C
>  	help
> -	 Say yes here to build support for Bosch Sensortec BMP280
> +	 Say yes here to build support for Bosch Sensortec BMP180 and BMP280
>  	 pressure and temperature sensor.
>  
>  	 To compile this driver as a module, choose M here: the module
> diff --git a/drivers/iio/pressure/bmp280.c b/drivers/iio/pressure/bmp280.c
> index a2602d8..8f64012 100644
> --- a/drivers/iio/pressure/bmp280.c
> +++ b/drivers/iio/pressure/bmp280.c
> @@ -1,12 +1,15 @@
>  /*
>   * Copyright (c) 2014 Intel Corporation
>   *
> - * Driver for Bosch Sensortec BMP280 digital pressure sensor.
> + * Driver for Bosch Sensortec BMP180 and BMP280 digital pressure sensor.
>   *
>   * This program is free software; you can redistribute it and/or modify
>   * it under the terms of the GNU General Public License version 2 as
>   * published by the Free Software Foundation.
>   *
> + * Datasheet:
> + * https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BMP180-DS000-121.pdf
> + * https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BMP280-DS001-12.pdf
>   */
>  
>  #define pr_fmt(fmt) "bmp280: " fmt
> @@ -15,9 +18,13 @@
>  #include <linux/i2c.h>
>  #include <linux/acpi.h>
>  #include <linux/regmap.h>
> +#include <linux/delay.h>
>  #include <linux/iio/iio.h>
>  #include <linux/iio/sysfs.h>
>  
> +/*
> + * BMP280 specific registers
> + */
>  #define BMP280_REG_TEMP_XLSB		0xFC
>  #define BMP280_REG_TEMP_LSB		0xFB
>  #define BMP280_REG_TEMP_MSB		0xFA
> @@ -26,10 +33,7 @@
>  #define BMP280_REG_PRESS_MSB		0xF7
>  
>  #define BMP280_REG_CONFIG		0xF5
> -#define BMP280_REG_CTRL_MEAS		0xF4
>  #define BMP280_REG_STATUS		0xF3
> -#define BMP280_REG_RESET		0xE0
> -#define BMP280_REG_ID			0xD0
>  
>  #define BMP280_REG_COMP_TEMP_START	0x88
>  #define BMP280_COMP_TEMP_REG_COUNT	6
> @@ -46,25 +50,53 @@
>  
>  #define BMP280_OSRS_TEMP_MASK		(BIT(7) | BIT(6) | BIT(5))
>  #define BMP280_OSRS_TEMP_SKIP		0
> -#define BMP280_OSRS_TEMP_1X		BIT(5)
> -#define BMP280_OSRS_TEMP_2X		BIT(6)
> -#define BMP280_OSRS_TEMP_4X		(BIT(6) | BIT(5))
> -#define BMP280_OSRS_TEMP_8X		BIT(7)
> -#define BMP280_OSRS_TEMP_16X		(BIT(7) | BIT(5))
> +#define BMP280_OSRS_TEMP_X(osrs_t)	((osrs_t) << 5)
> +#define BMP280_OSRS_TEMP_1X		BMP280_OSRS_TEMP_X(1)
> +#define BMP280_OSRS_TEMP_2X		BMP280_OSRS_TEMP_X(2)
> +#define BMP280_OSRS_TEMP_4X		BMP280_OSRS_TEMP_X(3)
> +#define BMP280_OSRS_TEMP_8X		BMP280_OSRS_TEMP_X(4)
> +#define BMP280_OSRS_TEMP_16X		BMP280_OSRS_TEMP_X(5)
>  
>  #define BMP280_OSRS_PRESS_MASK		(BIT(4) | BIT(3) | BIT(2))
>  #define BMP280_OSRS_PRESS_SKIP		0
> -#define BMP280_OSRS_PRESS_1X		BIT(2)
> -#define BMP280_OSRS_PRESS_2X		BIT(3)
> -#define BMP280_OSRS_PRESS_4X		(BIT(3) | BIT(2))
> -#define BMP280_OSRS_PRESS_8X		BIT(4)
> -#define BMP280_OSRS_PRESS_16X		(BIT(4) | BIT(2))
> +#define BMP280_OSRS_PRESS_X(osrs_p)	((osrs_p) << 2)
> +#define BMP280_OSRS_PRESS_1X		BMP280_OSRS_PRESS_X(1)
> +#define BMP280_OSRS_PRESS_2X		BMP280_OSRS_PRESS_X(2)
> +#define BMP280_OSRS_PRESS_4X		BMP280_OSRS_PRESS_X(3)
> +#define BMP280_OSRS_PRESS_8X		BMP280_OSRS_PRESS_X(4)
> +#define BMP280_OSRS_PRESS_16X		BMP280_OSRS_PRESS_X(5)
>  
>  #define BMP280_MODE_MASK		(BIT(1) | BIT(0))
>  #define BMP280_MODE_SLEEP		0
>  #define BMP280_MODE_FORCED		BIT(0)
>  #define BMP280_MODE_NORMAL		(BIT(1) | BIT(0))
>  
> +/*
> + * BMP180 specific registers
> + */
> +#define BMP180_REG_OUT_XLSB		0xF8
> +#define BMP180_REG_OUT_LSB		0xF7
> +#define BMP180_REG_OUT_MSB		0xF6
> +
> +#define BMP180_REG_CALIB_START		0xAA
> +#define BMP180_REG_CALIB_COUNT		22
> +
> +#define BMP180_MEAS_SCO			BIT(5)
> +#define BMP180_MEAS_TEMP		(0x0E | BMP180_MEAS_SCO)
> +#define BMP180_MEAS_PRESS_X(oss)	((oss) << 6 | 0x14 | BMP180_MEAS_SCO)
> +#define BMP180_MEAS_PRESS_1X		BMP180_MEAS_PRESS_X(0)
> +#define BMP180_MEAS_PRESS_2X		BMP180_MEAS_PRESS_X(1)
> +#define BMP180_MEAS_PRESS_4X		BMP180_MEAS_PRESS_X(2)
> +#define BMP180_MEAS_PRESS_8X		BMP180_MEAS_PRESS_X(3)
> +
> +/*
> + * BMP180 and BMP280 common registers
> + */
> +#define BMP280_REG_CTRL_MEAS		0xF4
> +#define BMP280_REG_RESET		0xE0
> +#define BMP280_REG_ID			0xD0
> +
> +#define BMP180_CHIP_ID			0x55
>  #define BMP280_CHIP_ID			0x58
>  #define BMP280_SOFT_RESET_VAL		0xB6
>  
> @@ -72,6 +104,15 @@ struct bmp280_data {
>  	struct i2c_client *client;
>  	struct mutex lock;
>  	struct regmap *regmap;
> +	const struct bmp280_ops *ops;
> +
> +	const int *oversampling_temp_avail;
> +	int num_oversampling_temp_avail;
> +	const int *oversampling_press_avail;
> +	int num_oversampling_press_avail;
> +
> +	u8 oversampling_press;
> +	u8 oversampling_temp;
>  
>  	/*
>  	 * Carryover value from temperature conversion, used in pressure
> @@ -80,9 +121,15 @@ struct bmp280_data {
>  	s32 t_fine;
>  };
>  
> +struct bmp280_ops {
> +	int (*init)(struct bmp280_data *);
> +	int (*read_temp)(struct bmp280_data *, int *);
> +	int (*read_press)(struct bmp280_data *, int *, int *);
> +};
> +
>  /*
>   * These enums are used for indexing into the array of compensation
> - * parameters.
> + * parameters for BMP280.
>   */
>  enum { T1, T2, T3 };
>  enum { P1, P2, P3, P4, P5, P6, P7, P8, P9 };
> @@ -90,11 +137,13 @@ enum { P1, P2, P3, P4, P5, P6, P7, P8, P9 };
>  static const struct iio_chan_spec bmp280_channels[] = {
>  	{
>  		.type = IIO_PRESSURE,
> -		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
> +				      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
>  	},
>  	{
>  		.type = IIO_TEMP,
> -		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
> +				      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
>  	},
>  };
>  
> @@ -290,10 +339,25 @@ static int bmp280_read_raw(struct iio_dev *indio_dev,
>  	case IIO_CHAN_INFO_PROCESSED:
>  		switch (chan->type) {
>  		case IIO_PRESSURE:
> -			ret = bmp280_read_press(data, val, val2);
> +			ret = data->ops->read_press(data, val, val2);
> +			break;
> +		case IIO_TEMP:
> +			ret = data->ops->read_temp(data, val);
> +			break;
> +		default:
> +			ret = -EINVAL;
> +			break;
> +		}
> +		break;
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		switch (chan->type) {
> +		case IIO_PRESSURE:
> +			*val = 1 << data->oversampling_press;
> +			ret = IIO_VAL_INT;
>  			break;
>  		case IIO_TEMP:
> -			ret = bmp280_read_temp(data, val);
> +			*val = 1 << data->oversampling_temp;
> +			ret = IIO_VAL_INT;
>  			break;
>  		default:
>  			ret = -EINVAL;
> @@ -310,22 +374,135 @@ static int bmp280_read_raw(struct iio_dev *indio_dev,
>  	return ret;
>  }
>  
> +static int bmp280_write_oversampling_ratio_temp(struct bmp280_data *data,
> +					       int val)
> +{
> +	int i;
> +	const int *avail = data->oversampling_temp_avail;
> +	const int n = data->num_oversampling_temp_avail;
> +
> +	for (i = 0; i < n; i++) {
> +		if (avail[i] == val) {
> +			data->oversampling_temp = ilog2(val);
> +
> +			return data->ops->init(data);
> +		}
> +	}
> +	return -EINVAL;
> +}
> +
> +static int bmp280_write_oversampling_ratio_press(struct bmp280_data *data,
> +					       int val)
> +{
> +	int i;
> +	const int *avail = data->oversampling_press_avail;
> +	const int n = data->num_oversampling_press_avail;
> +
> +	for (i = 0; i < n; i++) {
> +		if (avail[i] == val) {
> +			data->oversampling_press = ilog2(val);
> +
> +			return data->ops->init(data);

I find it odd that we're calling a function named "init" at something
other than initialization, maybe change it to "write_config" or
something similar?  But the logic for bmp280 seems good.

> +		}
> +	}
> +	return -EINVAL;
> +}
> +
> +static int bmp280_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	int ret = 0;
> +	struct bmp280_data *data = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		mutex_lock(&data->lock);
> +		switch (chan->type) {
> +		case IIO_PRESSURE:
> +			ret = bmp280_write_oversampling_ratio_press(data, val);
> +			break;
> +		case IIO_TEMP:
> +			ret = bmp280_write_oversampling_ratio_temp(data, val);
> +			break;
> +		default:
> +			ret = -EINVAL;
> +			break;
> +		}
> +		mutex_unlock(&data->lock);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return ret;
> +}
> +
> +static ssize_t bmp280_show_avail(char *buf, const int *vals, const int n)
> +{
> +	size_t len = 0;
> +	int i;
> +
> +	for (i = 0; i < n; i++)
> +		len += scnprintf(buf + len, PAGE_SIZE - len, "%d ", vals[i]);
> +
> +	buf[len - 1] = '\n';
> +
> +	return len;
> +}
> +
> +static ssize_t bmp280_show_temp_oversampling_avail(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	struct bmp280_data *data = iio_priv(dev_to_iio_dev(dev));
> +
> +	return bmp280_show_avail(buf, data->oversampling_temp_avail,
> +				 data->num_oversampling_temp_avail);
> +}
> +
> +static ssize_t bmp280_show_press_oversampling_avail(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	struct bmp280_data *data = iio_priv(dev_to_iio_dev(dev));
> +
> +	return bmp280_show_avail(buf, data->oversampling_press_avail,
> +				 data->num_oversampling_press_avail);
> +}
> +
> +static IIO_DEVICE_ATTR(in_temp_oversampling_ratio_available,
> +	S_IRUGO, bmp280_show_temp_oversampling_avail, NULL, 0);
> +
> +static IIO_DEVICE_ATTR(in_pressure_oversampling_ratio_available,
> +	S_IRUGO, bmp280_show_press_oversampling_avail, NULL, 0);
> +
> +static struct attribute *bmp280_attributes[] = {
> +	&iio_dev_attr_in_temp_oversampling_ratio_available.dev_attr.attr,
> +	&iio_dev_attr_in_pressure_oversampling_ratio_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group bmp280_attrs_group = {
> +	.attrs = bmp280_attributes,
> +};
> +
>  static const struct iio_info bmp280_info = {
>  	.driver_module = THIS_MODULE,
>  	.read_raw = &bmp280_read_raw,
> +	.write_raw = &bmp280_write_raw,
> +	.attrs = &bmp280_attrs_group,
>  };
>  
>  static int bmp280_chip_init(struct bmp280_data *data)
>  {
>  	int ret;
> +	u8 osrs = BMP280_OSRS_TEMP_X(data->oversampling_temp) |
> +		  BMP280_OSRS_PRESS_X(data->oversampling_press);
>  
>  	ret = regmap_update_bits(data->regmap, BMP280_REG_CTRL_MEAS,
>  				 BMP280_OSRS_TEMP_MASK |
>  				 BMP280_OSRS_PRESS_MASK |
>  				 BMP280_MODE_MASK,
> -				 BMP280_OSRS_TEMP_2X |
> -				 BMP280_OSRS_PRESS_16X |
> -				 BMP280_MODE_NORMAL);
> +				 osrs | BMP280_MODE_NORMAL);
>  	if (ret < 0) {
>  		dev_err(&data->client->dev,
>  			"failed to write ctrl_meas register\n");
> @@ -344,12 +521,315 @@ static int bmp280_chip_init(struct bmp280_data *data)
>  	return ret;
>  }
>  
> +static const int bmp280_oversampling_avail[] = { 1, 2, 4, 8, 16 };
> +
> +static const struct bmp280_ops bmp280_ops = {
> +	.init = bmp280_chip_init,
> +	.read_temp = bmp280_read_temp,
> +	.read_press = bmp280_read_press,
> +};
> +
> +static bool bmp180_is_writeable_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case BMP280_REG_CTRL_MEAS:
> +	case BMP280_REG_RESET:
> +		return true;
> +	default:
> +		return false;
> +	};
> +}
> +
> +static bool bmp180_is_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case BMP180_REG_OUT_XLSB:
> +	case BMP180_REG_OUT_LSB:
> +	case BMP180_REG_OUT_MSB:
> +	case BMP280_REG_CTRL_MEAS:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
> +static const struct regmap_config bmp180_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.max_register = BMP180_REG_OUT_XLSB,
> +	.cache_type = REGCACHE_RBTREE,
> +
> +	.writeable_reg = bmp180_is_writeable_reg,
> +	.volatile_reg = bmp180_is_volatile_reg,
> +};
> +
> +static int bmp180_measure(struct bmp280_data *data, u8 ctrl_meas)
> +{
> +	int ret;
> +	const int conversion_time_max[] = { 4500, 7500, 13500, 25500 };
> +	unsigned int delay_us;
> +	unsigned int ctrl;
> +
> +	ret = regmap_write(data->regmap, BMP280_REG_CTRL_MEAS, ctrl_meas);
> +	if (ret)
> +		return ret;
> +
> +	if (ctrl_meas == BMP180_MEAS_TEMP)
> +		delay_us = 4500;
> +	else
> +		delay_us = conversion_time_max[data->oversampling_press];
> +
> +	usleep_range(delay_us, delay_us + 1000);
> +
> +	ret = regmap_read(data->regmap, BMP280_REG_CTRL_MEAS, &ctrl);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * The value of this bit reset to "0" after conversion is complete
> +	 */
> +	if (ctrl & BMP180_MEAS_SCO)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int bmp180_read_adc_temp(struct bmp280_data *data, int *val)
> +{
> +	int ret;
> +	__be16 tmp = 0;
> +
> +	ret = bmp180_measure(data, BMP180_MEAS_TEMP);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB, (u8 *)&tmp, 2);
> +	if (ret)
> +		return ret;
> +
> +	*val = be16_to_cpu(tmp);
> +
> +	return 0;
> +}
> +
> +/*
> + * These enums are used for indexing into the array of calibration
> + * coefficients for BMP180.
> + */
> +enum { AC1, AC2, AC3, AC4, AC5, AC6, B1, B2, MB, MC, MD };
> +
> +struct bmp180_calib {
> +	s32 AC1;
> +	s32 AC2;
> +	s32 AC3;
> +	u32 AC4;
> +	u32 AC5;
> +	u32 AC6;
> +	s32 B1;
> +	s32 B2;
> +	s32 MB;
> +	s32 MC;
> +	s32 MD;
> +};
> +
> +static int bmp180_read_calib(struct bmp280_data *data,
> +			     struct bmp180_calib *calib)
> +{
> +	int ret;
> +	int i;
> +	__be16 buf[BMP180_REG_CALIB_COUNT / 2];
> +
> +	ret = regmap_bulk_read(data->regmap, BMP180_REG_CALIB_START, buf,
> +			       sizeof(buf));
> +
> +	/*
> +	 * None of the words has the value 0 or 0xFFFF
> +	 */
> +	for (i = 0; i < ARRAY_SIZE(buf); i++) {
> +		if (buf[i] == be16_to_cpu(0) || buf[i] == be16_to_cpu(0xffff))
> +			return -EIO;
> +	}
> +
> +	/*
> +	 * The double casts are necessary because be16_to_cpu returns an
> +	 * unsigned 16-bit value.  Casting that value directly to a
> +	 * signed 32-bit will not do proper sign extension.
> +	 *
> +	 * Conversely, AC4, AC5 and AC6 are unsigned values, so they can be
> +	 * cast straight to the larger type.
> +	 */
> +	calib->AC1 = (s32)(s16)be16_to_cpu(buf[AC1]);
> +	calib->AC2 = (s32)(s16)be16_to_cpu(buf[AC2]);
> +	calib->AC3 = (s32)(s16)be16_to_cpu(buf[AC3]);
> +	calib->AC4 = be16_to_cpu(buf[AC4]);
> +	calib->AC5 = be16_to_cpu(buf[AC5]);
> +	calib->AC6 = be16_to_cpu(buf[AC6]);
> +	calib->B1 = (s32)(s16)be16_to_cpu(buf[B1]);
> +	calib->B2 = (s32)(s16)be16_to_cpu(buf[B2]);
> +	calib->MB = (s32)(s16)be16_to_cpu(buf[MB]);
> +	calib->MC = (s32)(s16)be16_to_cpu(buf[MC]);
> +	calib->MD = (s32)(s16)be16_to_cpu(buf[MD]);
> +
> +	return 0;
> +}
> +
> +/*
> + * Returns temperature in DegC, resolution is 0.1 DegC.
> + * t_fine carries fine temperature as global value.
> + *
> + * Taken from datasheet, Section 3.5, "Calculating pressure and temperature".
> + */
> +static s32 bmp180_compensate_temp(struct bmp280_data *data, s32 adc_temp)
> +{
> +	int ret;
> +	s32 x1, x2;
> +	struct bmp180_calib calib;
> +
> +	ret = bmp180_read_calib(data, &calib);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev,
> +			"failed to read calibration coefficients\n");
> +		return ret;
> +	}
> +
> +	x1 = ((adc_temp - calib.AC6) * calib.AC5) >> 15;
> +	x2 = (calib.MC << 11) / (x1 + calib.MD);
> +	data->t_fine = x1 + x2;
> +
> +	return (data->t_fine + 8) >> 4;
> +}
> +
> +static int bmp180_read_temp(struct bmp280_data *data, int *val)
> +{
> +	int ret;
> +	s32 adc_temp, comp_temp;
> +
> +	ret = bmp180_read_adc_temp(data, &adc_temp);
> +	if (ret)
> +		return ret;
> +
> +	comp_temp = bmp180_compensate_temp(data, adc_temp);
> +
> +	/*
> +	 * val might be NULL if we're called by the read_press routine,
> +	 * who only cares about the carry over t_fine value.
> +	 */
> +	if (val) {
> +		*val = comp_temp * 100;
> +		return IIO_VAL_INT;
> +	}
> +
> +	return 0;
> +}
> +
> +static int bmp180_read_adc_press(struct bmp280_data *data, int *val)
> +{
> +	int ret;
> +	__be32 tmp = 0;
> +	u8 oss = data->oversampling_press;
> +
> +	ret = bmp180_measure(data, BMP180_MEAS_PRESS_X(oss));
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB, (u8 *)&tmp, 3);
> +	if (ret)
> +		return ret;
> +
> +	*val = (be32_to_cpu(tmp) >> 8) >> (8 - oss);
> +
> +	return 0;
> +}
> +
> +/*
> + * Returns pressure in Pa, resolution is 1 Pa.
> + *
> + * Taken from datasheet, Section 3.5, "Calculating pressure and temperature".
> + */
> +static u32 bmp180_compensate_press(struct bmp280_data *data, s32 adc_press)
> +{
> +	int ret;
> +	s32 x1, x2, x3, p;
> +	s32 b3, b6;
> +	u32 b4, b7;
> +	s32 oss = data->oversampling_press;
> +	struct bmp180_calib calib;
> +
> +	ret = bmp180_read_calib(data, &calib);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev,
> +			"failed to read calibration coefficients\n");
> +		return ret;
> +	}
> +
> +	b6 = data->t_fine - 4000;
> +	x1 = (calib.B2 * (b6 * b6 >> 12)) >> 11;
> +	x2 = calib.AC2 * b6 >> 11;
> +	x3 = x1 + x2;
> +	b3 = (((calib.AC1 * 4 + x3) << oss) + 2) / 4;
> +	x1 = calib.AC3 * b6 >> 13;
> +	x2 = (calib.B1 * ((b6 * b6) >> 12)) >> 16;
> +	x3 = (x1 + x2 + 2) >> 2;
> +	b4 = calib.AC4 * (u32)(x3 + 32768) >> 15;
> +	b7 = ((u32)adc_press - b3) * (50000 >> oss);
> +	if (b7 < 0x80000000)
> +		p = (b7 * 2) / b4;
> +	else
> +		p = (b7 / b4) * 2;
> +
> +	x1 = (p >> 8) * (p >> 8);
> +	x1 = (x1 * 3038) >> 16;
> +	x2 = (-7357 * p) >> 16;
> +
> +	return p + ((x1 + x2 + 3791) >> 4);
> +}
> +
> +static int bmp180_read_press(struct bmp280_data *data,
> +			     int *val, int *val2)
> +{
> +	int ret;
> +	s32 adc_press;
> +	u32 comp_press;
> +
> +	/* Read and compensate temperature so we get a reading of t_fine. */
> +	ret = bmp180_read_temp(data, NULL);
> +	if (ret)
> +		return ret;
> +
> +	ret = bmp180_read_adc_press(data, &adc_press);
> +	if (ret)
> +		return ret;
> +
> +	comp_press = bmp180_compensate_press(data, adc_press);
> +
> +	*val = comp_press;
> +	*val2 = 1000;
> +
> +	return IIO_VAL_FRACTIONAL;
> +}
> +
> +static int bmp180_chip_init(struct bmp280_data *data)
> +{
> +	return 0;
> +}

When setting the oversampling ratio, we do a lookup in the available
values array, then call ops->init to write the values to the register.
This function does nothing in the bmp180 case.  Or am I missing
something?

> +
> +static const int bmp180_oversampling_temp_avail[] = { 1 };
> +static const int bmp180_oversampling_press_avail[] = { 1, 2, 4, 8 };
> +
> +static const struct bmp280_ops bmp180_ops = {
> +	.read_temp = bmp180_read_temp,
> +	.read_press = bmp180_read_press,
> +	.init = bmp180_chip_init,
> +};
> +
>  static int bmp280_probe(struct i2c_client *client,
>  			const struct i2c_device_id *id)
>  {
>  	int ret;
>  	struct iio_dev *indio_dev;
>  	struct bmp280_data *data;
> +	const struct regmap_config *config;
>  	unsigned int chip_id;
>  
>  	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> @@ -367,7 +847,43 @@ static int bmp280_probe(struct i2c_client *client,
>  	indio_dev->info = &bmp280_info;
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  
> -	data->regmap = devm_regmap_init_i2c(client, &bmp280_regmap_config);
> +	switch (id->driver_data) {
> +	case BMP180_CHIP_ID:
> +		data->ops = &bmp180_ops;
> +
> +		data->oversampling_press_avail =
> +			bmp180_oversampling_press_avail;
> +		data->num_oversampling_press_avail =
> +			ARRAY_SIZE(bmp180_oversampling_press_avail);
> +		data->oversampling_press = ilog2(1);
> +
> +		data->oversampling_temp_avail = bmp180_oversampling_temp_avail;
> +		data->num_oversampling_temp_avail =
> +			ARRAY_SIZE(bmp180_oversampling_temp_avail);
> +		data->oversampling_temp = ilog2(1);
> +
> +		config = &bmp180_regmap_config;
> +		break;
> +	case BMP280_CHIP_ID:
> +		data->ops = &bmp280_ops;
> +
> +		data->oversampling_press_avail = bmp280_oversampling_avail;
> +		data->num_oversampling_press_avail =
> +			ARRAY_SIZE(bmp280_oversampling_avail);
> +		data->oversampling_press = ilog2(16);
> +
> +		data->oversampling_temp_avail = bmp280_oversampling_avail;
> +		data->num_oversampling_temp_avail =
> +			ARRAY_SIZE(bmp280_oversampling_avail);
> +		data->oversampling_temp = ilog2(2);
> +
> +		config = &bmp280_regmap_config;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	data->regmap = devm_regmap_init_i2c(client, config);
>  	if (IS_ERR(data->regmap)) {
>  		dev_err(&client->dev, "failed to allocate register map\n");
>  		return PTR_ERR(data->regmap);
> @@ -376,13 +892,13 @@ static int bmp280_probe(struct i2c_client *client,
>  	ret = regmap_read(data->regmap, BMP280_REG_ID, &chip_id);
>  	if (ret < 0)
>  		return ret;
> -	if (chip_id != BMP280_CHIP_ID) {
> +	if (chip_id != id->driver_data) {
>  		dev_err(&client->dev, "bad chip id.  expected %x got %x\n",
>  			BMP280_CHIP_ID, chip_id);
>  		return -EINVAL;
>  	}
>  
> -	ret = bmp280_chip_init(data);
> +	ret = data->ops->init(data);
>  	if (ret < 0)
>  		return ret;
>  
> @@ -390,13 +906,15 @@ static int bmp280_probe(struct i2c_client *client,
>  }
>  
>  static const struct acpi_device_id bmp280_acpi_match[] = {
> -	{"BMP0280", 0},
> +	{"BMP0280", BMP280_CHIP_ID },
>  	{ },
>  };
>  MODULE_DEVICE_TABLE(acpi, bmp280_acpi_match);
>  
>  static const struct i2c_device_id bmp280_id[] = {
> -	{"bmp280", 0},
> +	{"bmp280", BMP280_CHIP_ID },
> +	{"bmp180", BMP180_CHIP_ID },
> +	{"bmp085", BMP180_CHIP_ID },
>  	{ },
>  };
>  MODULE_DEVICE_TABLE(i2c, bmp280_id);
> @@ -412,5 +930,5 @@ static struct i2c_driver bmp280_driver = {
>  module_i2c_driver(bmp280_driver);
>  
>  MODULE_AUTHOR("Vlad Dogaru <vlad.dogaru@intel.com>");
> -MODULE_DESCRIPTION("Driver for Bosch Sensortec BMP280 pressure and temperature sensor");
> +MODULE_DESCRIPTION("Driver for Bosch Sensortec BMP180/BMP280 pressure and temperature sensor");
>  MODULE_LICENSE("GPL v2");
> -- 
> 2.5.0
>