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Date:   Sat, 19 Jan 2019 18:53:19 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Robert Eshleman <bobbyeshleman@gmail.com>
Cc:     Hartmut Knaack <knaack.h@gmx.de>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, linux-iio@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iio: light: add driver support for MAX44009
Message-ID: <20190119185319.4b20b939@archlinux>
In-Reply-To: <20190117065623.12169-1-bobbyeshleman@gmail.com>
References: <20190117065623.12169-1-bobbyeshleman@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, 16 Jan 2019 22:56:23 -0800
Robert Eshleman <bobbyeshleman@gmail.com> wrote:

Hi Robert,

Note I review drivers backwards, so comments may make more sense that
way around.

> 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:
> 
> * Rising and falling illuminance threshold
>   events

Not really on this one.  You support using them as a trigger, which
is not how threshold events should be handled in IIO. Please
report them as events.   This device doesn't seem  to have
a trigger that can be used in general, so you shouldn't provide
one.

Userspace can use the event to decide to do a read if it wants to
follow the classic move the thresholds so as to detect big
'changes' in light intensity.

Various other comments inline.  Quite a bit of style cleanup
needed as well, please check the kernel docs for coding style
https://www.kernel.org/doc/Documentation/process/coding-style.rst

Also take a look at other IIO drivers for the bits that are
noted in there as varying across the kernel.

Whilst there is quite a bit to work on in here yet, great to see
support for this new part! Looking forward to v2.

Jonathan

> 
> * Illuminance triggered buffers
> 
> * Integration time
> 
> https://datasheets.maximintegrated.com/en/ds/MAX44009.pdf
> 
> Signed-off-by: Robert Eshleman <bobbyeshleman@gmail.com>

> ---
>  .../bindings/iio/light/max44009.txt           |  25 +
>  drivers/iio/light/Kconfig                     |  13 +
>  drivers/iio/light/Makefile                    |   1 +
>  drivers/iio/light/max44009.c                  | 696 ++++++++++++++++++
>  4 files changed, 735 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/light/max44009.txt
>  create mode 100644 drivers/iio/light/max44009.c
> 
> diff --git a/Documentation/devicetree/bindings/iio/light/max44009.txt b/Documentation/devicetree/bindings/iio/light/max44009.txt
> new file mode 100644
> index 000000000000..220c2808dca1
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/light/max44009.txt
> @@ -0,0 +1,25 @@
> +* MAX44009 Ambient Light Sensor
> +
> +Required properties:
> +
> +- compatible: should be "maxim,max44009"
> +- reg: the I2C address of the device (default is <0x4a>)
> +
> +Optional properties:
> +
> +- interrupts : interrupt mapping for GPIO IRQ. Should be configured with
> +  IRQ_TYPE_EDGE_FALLING.
> +
> +Refer to interrupt-controller/interrupts.txt for generic interrupt client
> +node bindings.
> +
> +Example:
> +
> +max44009: max44009@4a {
> +	compatible = "maxim,max44009";
> +	reg = <0x4a>;
> +
> +	interrupt-parent = <&gpio1>;
> +	interrupts = <17 IRQ_TYPE_EDGE_FALLING>;
> +};
> +
> diff --git a/drivers/iio/light/Kconfig b/drivers/iio/light/Kconfig
> index 36f458433480..cda544f1047d 100644
> --- a/drivers/iio/light/Kconfig
> +++ b/drivers/iio/light/Kconfig
> @@ -299,6 +299,19 @@ 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
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +	select IIO_TRIGGERED_EVENT
> +	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..e15aa8eeb2f6
> --- /dev/null
> +++ b/drivers/iio/light/max44009.c
> @@ -0,0 +1,696 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * max44009.c - Support for MAX44009 Ambient Light Sensor
> + *
> + * Copyright (c) 2019 Robert Eshleman <bobbyeshleman@gmail.com>
> + *
> + * 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.
If you have SPDX, no need to have a license statement.
> + *
> + *
> + * Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX44009.pdf
> + *
> + * TODO: Support continuous mode and processed event value (IIO_EV_INFO_VALUE)
> + *
> + * Default I2C address: 0x4a
> + *
No point in this blank line.

> + */
> +
> +#include <linux/bits.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/events.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/trigger.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +#include <linux/util_macros.h>
> +
> +#define MAX44009_DRV_NAME "max44009"
> +#define MAX44009_IRQ_NAME "max44009_event"

Unless used more than once, no point in defines like this.  Just put
the string inline.

> +
> +/* Registers in datasheet order */
> +#define MAX44009_REG_STATUS 0x0
> +#define MAX44009_REG_ENABLE 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_INT_TIME_MASK (BIT(2) | BIT(1) | BIT(0))

GENMASK

> +#define MAX44009_INT_TIME_SHIFT (0)
> +
> +#define MAX44009_MANUAL_MODE_MASK BIT(6)
> +
> +/* The maxmimum raw rising threshold for the max44009 */
> +#define MAX44009_MAXIMUM_THRESHOLD 8355840
> +
> +#define MAX44009_HI_NIBBLE(reg) (((reg) >> 4) & 0xf)
> +#define MAX44009_LO_NIBBLE(reg) ((reg) & 0xf)
> +
> +#define MAX44009_EXP_MASK 0xf00
> +#define MAX44009_EXP_RSHIFT 8
> +#define MAX44009_LUX_EXP(reg)	                                              \
> +	(1 << (((reg) & MAX44009_EXP_MASK) >> MAX44009_EXP_RSHIFT))
> +#define MAX44009_LUX_MANT(reg) ((reg) & 0xff)
> +
> +#define MAX44009_LUX(reg) (MAX44009_LUX_EXP(reg) * MAX44009_LUX_MANT(reg))

These are complex enough that a few small functions with documentation
would be better than macros.

> +
> +#define MAX44009_THRESH_MANT(reg) ((MAX44009_LO_NIBBLE(reg) << 4) + 15)
> +#define MAX44009_THRESHOLD(reg)                                                \
> +	((1 << MAX44009_HI_NIBBLE(reg)) * MAX44009_THRESH_MANT(reg))
> +

> +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";
> +
> +static const u8 max44009_scale_avail_ulux_array[] = {45};
> +static const char max44009_scale_avail_str[] = "0.045";

If there is only one value, don't provide the avail stuff
and just put the value in directly where used.

> +
> +struct max44009_data {
> +	struct i2c_client *client;
> +	struct iio_trigger *trigger;
> +	struct mutex lock;
> +	int64_t timestamp;
> +};
> +
> +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_RAW),
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_INT_TIME),
> +		.scan_index = 0,
> +		.scan_type = {
> +				.sign = 'u',
> +				.realbits = 24,
> +				.storagebits = 32,
> +			},
> +		.event_spec = max44009_event_spec,
> +		.num_event_specs = ARRAY_SIZE(max44009_event_spec),
> +	},
> +	IIO_CHAN_SOFT_TIMESTAMP(1),
> +};
> +
> +static int max44009_read_reg(struct max44009_data *data, char reg)
> +{
> +	struct i2c_client *client = data->client;
> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +	ret = i2c_smbus_read_byte_data(client, reg);
> +	if (ret < 0) {

Same as below.

> +		dev_err(&client->dev,
> +			"failed to read reg 0x%0x, err: %d\n", reg, ret);
> +		goto err;
> +	}
> +
> +err:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +static int max44009_write_reg(struct max44009_data *data, char reg, char buf)
> +{
> +	struct i2c_client *client = data->client;
> +	int ret;
> +
> +	mutex_lock(&data->lock);

What is this mutex protecting?

> +	ret = i2c_smbus_write_byte_data(client, reg, buf);
> +	if (ret < 0) {

returns 0 on success.  So do
if (ret) as it'll prove simpler to follow for handling later.

> +		dev_err(&client->dev,
> +			"failed to write reg 0x%0x, err: %d\n",
> +			reg, ret);
> +		goto err;
> +	}
> +
> +err:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +static int max44009_read_int_time(struct max44009_data *data)
> +{
> +	int ret = max44009_read_reg(data, MAX44009_REG_CFG);
> +
> +	if (ret < 0) {
> +		return ret;
> +	}
> +
> +	return max44009_int_time_ns_array[ret & MAX44009_INT_TIME_MASK];
> +}
> +
> +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, int_time;
> +	s64 ns;
> +
> +	if (mask == IIO_CHAN_INFO_INT_TIME && chan->type == IIO_LIGHT) {
> +		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 = max44009_read_reg(data, MAX44009_REG_CFG);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret &= ~MAX44009_INT_TIME_MASK;
> +		ret |= (int_time << MAX44009_INT_TIME_SHIFT);
> +		ret |= MAX44009_MANUAL_MODE_MASK;
> +
> +		return max44009_write_reg(data, MAX44009_REG_CFG, ret);
> +	}
> +	return -EINVAL;
> +}
> +
> +static int max44009_write_raw_get_fmt(struct iio_dev *indio_dev,
> +				      struct iio_chan_spec const *chan,
> +				      long mask)
> +{
> +	if (mask == IIO_CHAN_INFO_INT_TIME && chan->type == IIO_LIGHT) {

Make sure to get rid of all the brackets where kernel style doesn't have them.
Basically any single statements if or else blocks (or simiilar).

> +		return IIO_VAL_INT_PLUS_NANO;
> +	} else {

You don't have any others...

> +		return IIO_VAL_INT;
> +	}
> +}
> +
> +#define READ_LUX_XFER_LEN (4)
> +
> +static int max44009_read_lux_raw(struct max44009_data *data)
> +{
> +	int ret;
> +	struct i2c_msg xfer[READ_LUX_XFER_LEN];
> +	u8 luxhireg[1] = {MAX44009_REG_LUX_HI};
> +	u8 luxloreg[1] = {MAX44009_REG_LUX_LO};
> +	u8 lo = 0;
> +	u8 hi = 0;
> +	u16 reg = 0;
> +
> +	xfer[0].addr = data->client->addr;
> +	xfer[0].flags = 0;
> +	xfer[0].len = 1;
> +	xfer[0].buf = luxhireg;
> +
> +	xfer[1].addr = data->client->addr;
> +	xfer[1].flags = I2C_M_RD;
> +	xfer[1].len = 1;
> +	xfer[1].buf = &hi;
> +
> +	xfer[2].addr = data->client->addr;
> +	xfer[2].flags = 0;
> +	xfer[2].len = 1;
> +	xfer[2].buf = luxloreg;
> +
> +	xfer[3].addr = data->client->addr;
> +	xfer[3].flags = I2C_M_RD;
> +	xfer[3].len = 1;
> +	xfer[3].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
> +	 */
> +	mutex_lock(&data->lock);
> +	ret = i2c_transfer(data->client->adapter, xfer, READ_LUX_XFER_LEN);
> +	mutex_unlock(&data->lock);
> +	if (ret != READ_LUX_XFER_LEN) {
> +		return -EIO;
> +	}
> +
> +	reg = (((u16)hi) << 4) | (lo & 0xf);

> +
> +	return MAX44009_LUX(reg);
> +}
> +
> +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 ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW: {
> +		switch (chan->type) {
> +		case IIO_LIGHT: {
> +			ret = max44009_read_lux_raw(data);
> +			if (ret < 0) {
> +				return ret;
> +			}
> +			*val = ret;
> +			*val2 = 0;
> +			return IIO_VAL_INT;
> +		}
> +		default:
> +			return -EINVAL;
> +		}
> +		break;
> +	}
> +
> +	case IIO_CHAN_INFO_INT_TIME: {
> +		ret = max44009_read_int_time(data);
> +		if (ret < 0) {
> +			return ret;
> +		}
> +
> +		*val2 = ret;
> +		*val = 0;
> +		return IIO_VAL_INT_PLUS_NANO;
> +	}
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static IIO_CONST_ATTR(illuminance_scale_available, max44009_scale_avail_str);
> +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,
> +	&iio_const_attr_illuminance_scale_available.dev_attr.attr, NULL
> +};
> +
> +static const struct attribute_group max44009_attribute_group = {
> +	.attrs = max44009_attributes,
> +};
> +
> +static int max44009_thresh_byte_from_int(int thresh)
> +{
> +	int mantissa, exp;
> +
> +	if (thresh < 0 || thresh > MAX44009_MAXIMUM_THRESHOLD) {
> +		return -EINVAL;
> +	}
> +
> +	for (mantissa = thresh, 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_thresh(struct iio_dev *indio_dev,
> +				 enum iio_event_direction dir, int val)
> +{
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int thresh;
> +	int reg;
> +
> +	reg = max44009_get_thr_reg(dir);
> +	if (reg < 0) {
> +		return reg;
> +	}
> +
> +	thresh = max44009_thresh_byte_from_int(val);
> +	if (thresh < 0) {
> +		return thresh;
> +	}
> +
> +	return max44009_write_reg(data, reg, thresh);
> +}
> +
> +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)
> +{
> +	if (info != IIO_EV_INFO_VALUE || chan->type != IIO_LIGHT || val2 != 0) {
> +		return -EINVAL;
> +	}
> +
> +	return max44009_write_thresh(indio_dev, dir, val);
> +}
> +
> +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 thresh, reg;
> +	struct max44009_data *data = iio_priv(indio_dev);
> +
> +	if (chan->type != IIO_LIGHT || type != IIO_EV_TYPE_THRESH) {
> +		return -EINVAL;
> +	}
> +
> +	reg = max44009_get_thr_reg(dir);
> +	if (reg < 0) {
> +		return reg;
> +	}
> +
> +	thresh = max44009_read_reg(data, reg);
> +	if (thresh < 0) {
> +		return thresh;
> +	}
> +
> +	*val = MAX44009_THRESHOLD(thresh);
> +
> +	return IIO_VAL_INT;
> +}
> +
> +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 = max44009_write_reg(data, MAX44009_REG_ENABLE, state);
> +	if (ret < 0) {
> +		return ret;
> +	}
> +
> +	/*
> +	 * Set device to trigger interrupt immediately upon exceeding
> +	 * the threshold limit
> +	 */
> +	ret = max44009_write_reg(data, MAX44009_REG_THR_TIMER, 0);
> +	if (ret < 0) {
> +		return ret;
> +	}
> +
> +	return 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);
> +	int ret;
> +
> +	if (chan->type != IIO_LIGHT || type != IIO_EV_TYPE_THRESH) {
> +		return -EINVAL;
> +	}
> +
> +	ret = max44009_read_reg(data, MAX44009_REG_ENABLE);
> +	if (ret < 0) {
> +		return ret;
> +	}
> +
> +	return ret;
> +}
We have lots of event config, but they are actually controlling the
trigger.  The device doesn't generate any iio events at all that I can see.

> +
> +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 int max44009_set_trigger_state(struct iio_trigger *trigger,
> +				      bool enable)
> +{
> +	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trigger);
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	ret = max44009_write_reg(data, MAX44009_REG_ENABLE, enable);
> +	if (ret < 0) {
> +		return ret;
> +	}
> +
> +	ret = max44009_write_reg(data, MAX44009_REG_THR_TIMER, 0);
> +	if (ret < 0) {
As suggested above, write_reg should clearly only return 0 or negative.
you can just do
return max440..

> +		return ret;
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct iio_trigger_ops max44009_trigger_ops = {
> +	.set_trigger_state = max44009_set_trigger_state,
> +};
> +
> +static irqreturn_t max44009_trigger_handler(int irq, void *p)
> +{
> +	struct iio_dev *indio_dev = p;
> +	struct max44009_data *data = iio_priv(indio_dev);
> +	int lux, upper, lower;
> +	int ret;
> +	enum iio_event_direction direction;
> +
> +	/* 32-bit for lux and 64-bit for timestamp */
> +	u32 buf[3] = {0};

Except the timestamp needs to be 64 bit aligned so this isn't big enough.
All elements in IIO buffers are 'naturally' aligned. so 32 bit is
aligned to 32 bits, 64 to 64 bits.

> +
> +	ret = max44009_read_reg(data, MAX44009_REG_STATUS);
> +	if (ret <= 0) {
> +		goto err;
> +	}
> +
> +	ret = max44009_read_reg(data, MAX44009_REG_ENABLE);
> +	if (ret <= 0) {
> +		goto err;
> +	}

If these reads are necessary, then add comments on why.

> +
> +	/* Clear interrupt by disabling interrupt (see datasheet) */
> +	ret = max44009_write_reg(data, MAX44009_REG_ENABLE, 0);
> +	if (ret < 0) {
> +		goto err;
> +	}
> +
> +	lux = max44009_read_lux_raw(data);
> +	if (lux < 0) {
> +		goto err;
> +	}
> +
> +	upper = max44009_read_reg(data, MAX44009_REG_UPPER_THR);
> +	if (upper < 0) {
> +		goto err;
> +	}
> +	upper = MAX44009_THRESHOLD(upper);
> +
> +	lower = max44009_read_reg(data, MAX44009_REG_LOWER_THR);
> +	if (lower < 0) {
> +		goto err;
> +	}
> +	lower = MAX44009_THRESHOLD(lower);
> +
> +	/* If lux is NOT out-of-bounds then the interrupt was not triggered
> +	 * by this device
Multiline comment syntax in IIO (and most of the kernel) is
/*
 * If...
 */

Do we support shared interrupt lines?  Doesn't look like it, which means
it 'probably was' generate by this device, but we don't know why because the value
has changed.

Returning IRQ_NONE is a bad idea unless we are pretty sure it is a spurious
interrupt, or we have a shared interrupt line.  It will ultimately result
in your interrupt being disable by the kernel and all activity breaking.

There is also a perfectly good register to tell use if we generated the interrupt.
Read that one and use that, not this racey approach.

> +	 */
> +	if (lux < upper && lux > lower) {
> +		goto err;
> +	}
> +
> +	/* Get event for correct thresh direction */
> +	if (lux >= upper) {
> +		direction = IIO_EV_DIR_RISING;
> +	} else if (lux <= lower) {
> +		direction = IIO_EV_DIR_FALLING;
> +	} else {
> +		goto err;
> +	}
> +
> +	buf[0] = lux;
> +	iio_push_to_buffers_with_timestamp(indio_dev, &buf, data->timestamp);
> +	iio_trigger_notify_done(data->trigger);
> +
> +	iio_push_event(indio_dev,
> +		       IIO_UNMOD_EVENT_CODE(IIO_LIGHT, 0,
> +					    IIO_EV_TYPE_THRESH, direction),
> +		       data->timestamp);
> +
> +	ret = max44009_write_reg(data, MAX44009_REG_ENABLE, 1);
> +	if (ret < 0) {
> +		goto err;
> +	}
> +
> +	return IRQ_HANDLED;
> +
> +err:
> +	/* Re-enable interrupt */
> +	max44009_write_reg(data, MAX44009_REG_ENABLE, 1);
> +	return IRQ_NONE;
> +}
> +
> +static irqreturn_t max44009_irq_handler(int irq, void *p)
> +{
> +	struct iio_dev *indio_dev = p;
> +	struct max44009_data *data = iio_priv(indio_dev);
> +
> +	data->timestamp = iio_get_time_ns(indio_dev);

We have a standard core function to do this..
iio_pollfunc_store_time.

There 'might' be a reason to do it differently depending
on whether you really need it to be that good if you
can't identify whether it is your interrupt until the
interrupt thread.


> +	return IRQ_WAKE_THREAD;
> +}
> +
> +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 stale interrupt bit */
> +	ret = max44009_read_reg(data, MAX44009_REG_STATUS);
> +	if (ret < 0) {
> +		goto err;
> +	}
> +
> +	if (client->irq > 0) {
> +		ret = devm_request_threaded_irq(&client->dev, client->irq,
> +						max44009_irq_handler,

This is wrong. The interrupt handler should call the iio_trigger_poll functions
to cause the trigger handlers for all attached devices to be called.

If for some reason the trigger is only suitable for use by this device
then things get more blurred, but if not, the interrupt handler itself
should establish that the interrupt is the data ready signal and call
iio_trigger_poll.  If it is in a thread, call iio_trigger_poll_chained.

The interrupt should be cleared (if it hasn't naturally happened for
some other reason, in the trigger try_reenable callback.


> +						max44009_trigger_handler,
> +						IRQF_TRIGGER_FALLING |
> +						IRQF_ONESHOT,
> +						MAX44009_IRQ_NAME, indio_dev);
> +		if (ret < 0) {
> +			goto err;
> +		}
> +
> +		ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev,
> +						      max44009_irq_handler,
> +						      max44009_trigger_handler,
> +						      NULL);
> +		if (ret < 0) {

It's going to change anyway (see below) but note kernel style is no
brackets when only one item in an block like this.

> +			goto err;
> +		}
> +
> +		data->trigger = devm_iio_trigger_alloc(indio_dev->dev.parent,
> +						       "%s-dev%d",
> +						       indio_dev->name,
> +						       indio_dev->id);
> +		if (!data->trigger) {
> +			ret = -ENOMEM;
> +			goto err;
> +		}
> +		data->trigger->dev.parent = indio_dev->dev.parent;
> +		data->trigger->ops = &max44009_trigger_ops;
> +		iio_trigger_set_drvdata(data->trigger, indio_dev);
> +
> +		ret = devm_iio_trigger_register(&client->dev, data->trigger);
> +		if (ret < 0) {
> +			goto err;
> +		}
> +	}
> +
> +	ret = devm_iio_device_register(&client->dev, indio_dev);
> +	if (ret < 0) {
> +		goto err;

Without the mutex destroy these all just become return ret;

> +	}
> +
> +	return 0;
> +err:
> +	mutex_destroy(&data->lock);

mutex destroy is only really useful for lock debugging.  Given we don't
leave anything behind here anyway, it just makes the flow more complex
for no gain.  We very rarely bother with it as a result.

> +	return ret;
> +}
> +
> +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@gmail.com>");
> +MODULE_LICENSE("GPL v2");
> +MODULE_VERSION("1.0.0");
Please drop.  MODULE_VERSION provides very little useful info
and tends to lead to people assuming it does.

Userspace has no obligation to ever look at it and we can't
break userspace that doesn't so it doesn't provide any value.

> +MODULE_DESCRIPTION("MAX44009 ambient light sensor driver");