Date:   Sat, 2 Feb 2019 15:50:20 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Robert Eshleman <bobbyeshleman@...il.com>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] iio: light: add driver for MAX44009

On Thu, 31 Jan 2019 07:29:01 -0800
Robert Eshleman <bobbyeshleman@...il.com> wrote:

> The MAX44009 is a low-power ambient light sensor from Maxim
> Integrated. It differs from the MAX44000 in that it doesn't have
> proximity sensing and that it requires far less current (1 micro-amp
> vs 5 micro-amps). The register mapping and feature set between the
> two are different enough to require a new driver for the MAX44009.
> 
> Developed and tested with a BeagleBone Black and UDOO Neo (i.MX6SX)
> 
> Supported features:
> 
> * Reading lux (processed value)
> 
> * Rising and falling illuminance threshold
>   events
> 
> * Configuring integration time
> 
> https://datasheets.maximintegrated.com/en/ds/MAX44009.pdf
> 
> Signed-off-by: Robert Eshleman <bobbyeshleman@...il.com>
Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan

> ---
> Changes to v4:
> - Reformat subject line
> - Clean up whitespace
> 
> Changes to v3:
> - Remove unnecessary mask when setting integration time
> - Return IRQ_NONE in IRQ handler when interrupt not from this device
> - Fix incorrect register usage when reading lux low byte
> - Clean up style
> 
> Changes to v2:
> - Remove unnecessary mutex locking
> - Remove unnecessary triggered buffer support
> - Remove unnecessary wrapper functions for smbus reads and writes
> - Remove scale avail support
> - Use constant scale to provide processed values instead of raw
> - Remove IRQ_NONE return for non-shared IRQ
> - Clean up style
> 
>  drivers/iio/light/Kconfig    |  10 +
>  drivers/iio/light/Makefile   |   1 +
>  drivers/iio/light/max44009.c | 555 +++++++++++++++++++++++++++++++++++
>  3 files changed, 566 insertions(+)
>  create mode 100644 drivers/iio/light/max44009.c
> 
> diff --git a/drivers/iio/light/Kconfig b/drivers/iio/light/Kconfig
> index 36f458433480..5190eacfeb0a 100644
> --- a/drivers/iio/light/Kconfig
> +++ b/drivers/iio/light/Kconfig
> @@ -299,6 +299,16 @@ config MAX44000
>  	 To compile this driver as a module, choose M here:
>  	 the module will be called max44000.
>  
> +config MAX44009
> +	tristate "MAX44009 Ambient Light Sensor"
> +	depends on I2C
> +	help
> +	 Say Y here if you want to build support for Maxim Integrated's
> +	 MAX44009 ambient light sensor device.
> +
> +	 To compile this driver as a module, choose M here:
> +	 the module will be called max44009.
> +
>  config OPT3001
>  	tristate "Texas Instruments OPT3001 Light Sensor"
>  	depends on I2C
> diff --git a/drivers/iio/light/Makefile b/drivers/iio/light/Makefile
> index 286bf3975372..e40794fbb435 100644
> --- a/drivers/iio/light/Makefile
> +++ b/drivers/iio/light/Makefile
> @@ -28,6 +28,7 @@ obj-$(CONFIG_SENSORS_LM3533)	+= lm3533-als.o
>  obj-$(CONFIG_LTR501)		+= ltr501.o
>  obj-$(CONFIG_LV0104CS)		+= lv0104cs.o
>  obj-$(CONFIG_MAX44000)		+= max44000.o
> +obj-$(CONFIG_MAX44009)		+= max44009.o
>  obj-$(CONFIG_OPT3001)		+= opt3001.o
>  obj-$(CONFIG_PA12203001)	+= pa12203001.o
>  obj-$(CONFIG_RPR0521)		+= rpr0521.o
> diff --git a/drivers/iio/light/max44009.c b/drivers/iio/light/max44009.c
> new file mode 100644
> index 000000000000..00ba15499638
> --- /dev/null
> +++ b/drivers/iio/light/max44009.c
> @@ -0,0 +1,555 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * max44009.c - Support for MAX44009 Ambient Light Sensor
> + *
> + * Copyright (c) 2019 Robert Eshleman <bobbyeshleman@...il.com>
> + *
> + * Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX44009.pdf
> + *
> + * TODO: Support continuous mode and configuring from manual mode to
> + *	 automatic mode.
> + *
> + * Default I2C address: 0x4a
> + */
> +
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/bits.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/events.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/util_macros.h>
> +
> +#define MAX44009_DRV_NAME "max44009"
> +
> +/* Registers in datasheet order */
> +#define MAX44009_REG_INT_STATUS 0x0
> +#define MAX44009_REG_INT_EN 0x1
> +#define MAX44009_REG_CFG 0x2
> +#define MAX44009_REG_LUX_HI 0x3
> +#define MAX44009_REG_LUX_LO 0x4
> +#define MAX44009_REG_UPPER_THR 0x5
> +#define MAX44009_REG_LOWER_THR 0x6
> +#define MAX44009_REG_THR_TIMER 0x7
> +
> +#define MAX44009_CFG_TIM_MASK GENMASK(2, 0)
> +#define MAX44009_CFG_MAN_MODE_MASK BIT(6)
> +
> +/* The maximum rising threshold for the max44009 */
> +#define MAX44009_MAXIMUM_THRESHOLD 7520256
> +
> +#define MAX44009_THRESH_EXP_MASK (0xf << 4)
> +#define MAX44009_THRESH_EXP_RSHIFT 4
> +#define MAX44009_THRESH_MANT_LSHIFT 4
> +#define MAX44009_THRESH_MANT_MASK 0xf
> +
> +#define MAX44009_UPPER_THR_MINIMUM 15
> +
> +/* The max44009 always scales raw readings by 0.045 and is non-configurable */
> +#define MAX44009_SCALE_NUMERATOR 45
> +#define MAX44009_SCALE_DENOMINATOR 1000
> +
> +/* The fixed-point fractional multiplier for de-scaling threshold values */
> +#define MAX44009_FRACT_MULT 1000000
> +
> +static const u32 max44009_int_time_ns_array[] = {
> +	800000000,
> +	400000000,
> +	200000000,
> +	100000000,
> +	50000000, /* Manual mode only */
> +	25000000, /* Manual mode only */
> +	12500000, /* Manual mode only */
> +	6250000,  /* Manual mode only */
> +};
> +
> +static const char max44009_int_time_str[] =
> +	"0.8 "
> +	"0.4 "
> +	"0.2 "
> +	"0.1 "
> +	"0.05 "
> +	"0.025 "
> +	"0.0125 "
> +	"0.00625";
> +
> +struct max44009_data {
> +	struct i2c_client *client;
> +	struct mutex lock;
> +};
> +
> +static const struct iio_event_spec max44009_event_spec[] = {
> +	{
> +		.type = IIO_EV_TYPE_THRESH,
> +		.dir = IIO_EV_DIR_RISING,
> +		.mask_separate = BIT(IIO_EV_INFO_VALUE) |
> +				 BIT(IIO_EV_INFO_ENABLE),
> +	},
> +	{
> +		.type = IIO_EV_TYPE_THRESH,
> +		.dir = IIO_EV_DIR_FALLING,
> +		.mask_separate = BIT(IIO_EV_INFO_VALUE) |
> +				 BIT(IIO_EV_INFO_ENABLE),
> +	},
> +};
> +
> +static const struct iio_chan_spec max44009_channels[] = {
> +	{
> +		.type = IIO_LIGHT,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
> +				      BIT(IIO_CHAN_INFO_INT_TIME),
> +		.event_spec = max44009_event_spec,
> +		.num_event_specs = ARRAY_SIZE(max44009_event_spec),
> +	},
> +};
> +
> +static int max44009_read_int_time(struct max44009_data *data)
> +{
> +
> +	int ret = i2c_smbus_read_byte_data(data->client, MAX44009_REG_CFG);
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	return max44009_int_time_ns_array[ret & MAX44009_CFG_TIM_MASK];
> +}
> +
> +static int max44009_write_int_time(struct max44009_data *data,
> +				   int val, int val2)
> +{
> +	struct i2c_client *client = data->client;
> +	int ret, int_time, config;
> +	s64 ns;
> +
> +	ns = val * NSEC_PER_SEC + val2;
> +	int_time = find_closest_descending(
> +			ns,
> +			max44009_int_time_ns_array,
> +			ARRAY_SIZE(max44009_int_time_ns_array));
> +
> +	ret = i2c_smbus_read_byte_data(client, MAX44009_REG_CFG);
> +	if (ret < 0)
> +		return ret;
> +
> +	config = ret;
> +	config &= int_time;
> +
> +	/*
> +	 * To set the integration time, the device must also be in manual
> +	 * mode.
> +	 */
> +	config |= MAX44009_CFG_MAN_MODE_MASK;
> +
> +	return i2c_smbus_write_byte_data(client, MAX44009_REG_CFG, config);
> +}
> +
> +static int max44009_write_raw(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan, int val,
> +			      int val2, long mask)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (mask == IIO_CHAN_INFO_INT_TIME && chan->type == IIO_LIGHT) {
> +		mutex_lock(&data->lock);
> +		ret = max44009_write_int_time(data, val, val2);
> +		mutex_unlock(&data->lock);
> +		return ret;
> +	}
> +	return -EINVAL;
> +}
> +
> +static int max44009_write_raw_get_fmt(struct iio_dev *indio_dev,
> +				      struct iio_chan_spec const *chan,
> +				      long mask)
> +{
> +	return IIO_VAL_INT_PLUS_NANO;
> +}
> +
> +static int max44009_lux_raw(u8 hi, u8 lo)
> +{
> +	int mantissa;
> +	int exponent;
> +
> +	/*
> +	 * The mantissa consists of the low nibble of the Lux High Byte
> +	 * and the low nibble of the Lux Low Byte.
> +	 */
> +	mantissa = ((hi & 0xf) << 4) | (lo & 0xf);
> +
> +	/* The exponent byte is just the upper nibble of the Lux High Byte */
> +	exponent = (hi >> 4) & 0xf;
> +
> +	/*
> +	 * The exponent value is base 2 to the power of the raw exponent byte.
> +	 */
> +	exponent = 1 << exponent;
> +
> +	return exponent * mantissa;
> +}
> +
> +#define MAX44009_READ_LUX_XFER_LEN (4)
> +
> +static int max44009_read_lux_raw(struct max44009_data *data)
> +{
> +	int ret;
> +	u8 hireg = MAX44009_REG_LUX_HI;
> +	u8 loreg = MAX44009_REG_LUX_LO;
> +	u8 lo = 0;
> +	u8 hi = 0;
> +
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = data->client->addr,
> +			.flags = 0,
> +			.len = sizeof(hireg),
> +			.buf = &hireg,
> +		},
> +		{
> +			.addr = data->client->addr,
> +			.flags = I2C_M_RD,
> +			.len = sizeof(hi),
> +			.buf = &hi,
> +		},
> +		{
> +			.addr = data->client->addr,
> +			.flags = 0,
> +			.len = sizeof(loreg),
> +			.buf = &loreg,
> +		},
> +		{
> +			.addr = data->client->addr,
> +			.flags = I2C_M_RD,
> +			.len = sizeof(lo),
> +			.buf = &lo,
> +		}
> +	};
> +
> +	/*
> +	 * Use i2c_transfer instead of smbus read because i2c_transfer
> +	 * does NOT use a stop bit between address write and data read.
> +	 * Using a stop bit causes disjoint upper/lower byte reads and
> +	 * reduces accuracy.
> +	 */
> +	ret = i2c_transfer(data->client->adapter,
> +			   msgs, MAX44009_READ_LUX_XFER_LEN);
> +
> +	if (ret != MAX44009_READ_LUX_XFER_LEN)
> +		return -EIO;
> +
> +	return max44009_lux_raw(hi, lo);
> +}
> +
> +static int max44009_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan, int *val,
> +			     int *val2, long mask)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int lux_raw;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_PROCESSED:
> +		switch (chan->type) {
> +		case IIO_LIGHT:
> +			ret = max44009_read_lux_raw(data);
> +			if (ret < 0)
> +				return ret;
> +			lux_raw = ret;
> +
> +			*val = lux_raw * MAX44009_SCALE_NUMERATOR;
> +			*val2 = MAX44009_SCALE_DENOMINATOR;
> +			return IIO_VAL_FRACTIONAL;
> +		default:
> +			return -EINVAL;
> +		}
> +	case IIO_CHAN_INFO_INT_TIME:
> +		switch (chan->type) {
> +		case IIO_LIGHT:
> +			ret = max44009_read_int_time(data);
> +			if (ret < 0)
> +				return ret;
> +
> +			*val2 = ret;
> +			*val = 0;
> +			return IIO_VAL_INT_PLUS_NANO;
> +		default:
> +			return -EINVAL;
> +		}
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static IIO_CONST_ATTR(illuminance_integration_time_available,
> +		      max44009_int_time_str);
> +
> +static struct attribute *max44009_attributes[] = {
> +	&iio_const_attr_illuminance_integration_time_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group max44009_attribute_group = {
> +	.attrs = max44009_attributes,
> +};
> +
> +static int max44009_threshold_byte_from_fraction(int integral, int fractional)
> +{
> +	int mantissa, exp;
> +
> +	if ((integral <= 0 && fractional <= 0) ||
> +	     integral > MAX44009_MAXIMUM_THRESHOLD ||
> +	     (integral == MAX44009_MAXIMUM_THRESHOLD && fractional != 0))
> +		return -EINVAL;
> +
> +	/* Reverse scaling of fixed-point integral */
> +	mantissa = integral * MAX44009_SCALE_DENOMINATOR;
> +	mantissa /= MAX44009_SCALE_NUMERATOR;
> +
> +	/* Reverse scaling of fixed-point fractional */
> +	mantissa += fractional / MAX44009_FRACT_MULT *
> +		    (MAX44009_SCALE_DENOMINATOR / MAX44009_SCALE_NUMERATOR);
> +
> +	for (exp = 0; mantissa > 0xff; exp++)
> +		mantissa >>= 1;
> +
> +	mantissa >>= 4;
> +	mantissa &= 0xf;
> +	exp <<= 4;
> +
> +	return exp | mantissa;
> +}
> +
> +static int max44009_get_thr_reg(enum iio_event_direction dir)
> +{
> +	switch (dir) {
> +	case IIO_EV_DIR_RISING:
> +		return MAX44009_REG_UPPER_THR;
> +	case IIO_EV_DIR_FALLING:
> +		return MAX44009_REG_LOWER_THR;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int max44009_write_event_value(struct iio_dev *indio_dev,
> +				      const struct iio_chan_spec *chan,
> +				      enum iio_event_type type,
> +				      enum iio_event_direction dir,
> +				      enum iio_event_info info,
> +				      int val, int val2)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int reg, threshold;
> +
> +	if (info != IIO_EV_INFO_VALUE || chan->type != IIO_LIGHT)
> +		return -EINVAL;
> +
> +	threshold = max44009_threshold_byte_from_fraction(val, val2);
> +	if (threshold < 0)
> +		return threshold;
> +
> +	reg = max44009_get_thr_reg(dir);
> +	if (reg < 0)
> +		return reg;
> +
> +	return i2c_smbus_write_byte_data(data->client, reg, threshold);
> +}
> +
> +static int max44009_read_threshold(struct iio_dev *indio_dev,
> +				   enum iio_event_direction dir)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int byte, reg;
> +	int mantissa, exponent;
> +
> +	reg = max44009_get_thr_reg(dir);
> +	if (reg < 0)
> +		return reg;
> +
> +	byte = i2c_smbus_read_byte_data(data->client, reg);
> +	if (byte < 0)
> +		return byte;
> +
> +	mantissa = byte & MAX44009_THRESH_MANT_MASK;
> +	mantissa <<= MAX44009_THRESH_MANT_LSHIFT;
> +
> +	/*
> +	 * To get the upper threshold, always adds the minimum upper threshold
> +	 * value to the shifted byte value (see datasheet).
> +	 */
> +	if (dir == IIO_EV_DIR_RISING)
> +		mantissa += MAX44009_UPPER_THR_MINIMUM;
> +
> +	/*
> +	 * Exponent is base 2 to the power of the threshold exponent byte
> +	 * value
> +	 */
> +	exponent = byte & MAX44009_THRESH_EXP_MASK;
> +	exponent >>= MAX44009_THRESH_EXP_RSHIFT;
> +
> +	return (1 << exponent) * mantissa;
> +}
> +
> +static int max44009_read_event_value(struct iio_dev *indio_dev,
> +				     const struct iio_chan_spec *chan,
> +				     enum iio_event_type type,
> +				     enum iio_event_direction dir,
> +				     enum iio_event_info info,
> +				     int *val, int *val2)
> +{
> +	int ret;
> +	int threshold;
> +
> +	if (chan->type != IIO_LIGHT || type != IIO_EV_TYPE_THRESH)
> +		return -EINVAL;
> +
> +	ret = max44009_read_threshold(indio_dev, dir);
> +	if (ret < 0)
> +		return ret;
> +	threshold = ret;
> +
> +	*val = threshold * MAX44009_SCALE_NUMERATOR;
> +	*val2 = MAX44009_SCALE_DENOMINATOR;
> +
> +	return IIO_VAL_FRACTIONAL;
> +}
> +
> +static int max44009_write_event_config(struct iio_dev *indio_dev,
> +				       const struct iio_chan_spec *chan,
> +				       enum iio_event_type type,
> +				       enum iio_event_direction dir,
> +				       int state)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (chan->type != IIO_LIGHT || type != IIO_EV_TYPE_THRESH)
> +		return -EINVAL;
> +
> +	ret = i2c_smbus_write_byte_data(data->client,
> +					MAX44009_REG_INT_EN, state);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * Set device to trigger interrupt immediately upon exceeding
> +	 * the threshold limit.
> +	 */
> +	return i2c_smbus_write_byte_data(data->client,
> +					 MAX44009_REG_THR_TIMER, 0);
> +}
> +
> +static int max44009_read_event_config(struct iio_dev *indio_dev,
> +				      const struct iio_chan_spec *chan,
> +				      enum iio_event_type type,
> +				      enum iio_event_direction dir)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +
> +	if (chan->type != IIO_LIGHT || type != IIO_EV_TYPE_THRESH)
> +		return -EINVAL;
> +
> +	return i2c_smbus_read_byte_data(data->client, MAX44009_REG_INT_EN);
> +}
> +
> +static const struct iio_info max44009_info = {
> +	.read_raw = max44009_read_raw,
> +	.write_raw = max44009_write_raw,
> +	.write_raw_get_fmt = max44009_write_raw_get_fmt,
> +	.read_event_value = max44009_read_event_value,
> +	.read_event_config = max44009_read_event_config,
> +	.write_event_value = max44009_write_event_value,
> +	.write_event_config = max44009_write_event_config,
> +	.attrs = &max44009_attribute_group,
> +};
> +
> +static irqreturn_t max44009_threaded_irq_handler(int irq, void *p)
> +{
> +	struct iio_dev *indio_dev = p;
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	ret = i2c_smbus_read_byte_data(data->client, MAX44009_REG_INT_STATUS);
> +	if (ret) {
> +		iio_push_event(indio_dev,
> +			       IIO_UNMOD_EVENT_CODE(IIO_LIGHT, 0,
> +						    IIO_EV_TYPE_THRESH,
> +						    IIO_EV_DIR_EITHER),
> +			       iio_get_time_ns(indio_dev));
> +
> +		return IRQ_HANDLED;
> +	}
> +
> +	return IRQ_NONE;
> +}
> +
> +static int max44009_probe(struct i2c_client *client,
> +			  const struct i2c_device_id *id)
> +{
> +	struct max44009_data *data;
> +	struct iio_dev *indio_dev;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	i2c_set_clientdata(client, indio_dev);
> +	data->client = client;
> +	indio_dev->dev.parent = &client->dev;
> +	indio_dev->info = &max44009_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->name = MAX44009_DRV_NAME;
> +	indio_dev->channels = max44009_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max44009_channels);
> +	mutex_init(&data->lock);
> +
> +	/* Clear any stale interrupt bit */
> +	ret = i2c_smbus_read_byte_data(client, MAX44009_REG_CFG);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (client->irq > 0) {
> +		ret = devm_request_threaded_irq(&client->dev, client->irq,
> +						NULL,
> +						max44009_threaded_irq_handler,
> +						IRQF_TRIGGER_FALLING |
> +						IRQF_ONESHOT | IRQF_SHARED,
> +						"max44009_event",
> +						indio_dev);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	return devm_iio_device_register(&client->dev, indio_dev);
> +}
> +
> +static const struct i2c_device_id max44009_id[] = {
> +	{ "max44009", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, max44009_id);
> +
> +static struct i2c_driver max44009_driver = {
> +	.driver = {
> +		.name = MAX44009_DRV_NAME,
> +	},
> +	.probe = max44009_probe,
> +	.id_table = max44009_id,
> +};
> +module_i2c_driver(max44009_driver);
> +
> +static const struct of_device_id max44009_of_match[] = {
> +	{ .compatible = "maxim,max44009" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, max44009_of_match);
> +
> +MODULE_AUTHOR("Robert Eshleman <bobbyeshleman@...il.com>");
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("MAX44009 ambient light sensor driver");

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