Message-ID: <20221023131933.57966858@jic23-huawei>
Date:   Sun, 23 Oct 2022 13:19:33 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
Cc:     lars@...afoo.de, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, rajat.khandelwal@...el.com
Subject: Re: [PATCH v4] iio: temperature: Add driver support for Maxim
 MAX30208

On Thu, 20 Oct 2022 22:52:18 +0530
Rajat Khandelwal <rajat.khandelwal@...ux.intel.com> wrote:

> Maxim MAX30208 is a digital temperature sensor with 0.1°C accuracy.
> 
> Add support for max30208 driver in iio subsystem.
> Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX30208.pdf
> 
> Signed-off-by: Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>

Hi Rajat, review on basis that v5 will be cc'd to 
HARDWARE MONITORING
M:	Jean Delvare <jdelvare@...e.com>
M:	Guenter Roeck <linux@...ck-us.net>
L:	linux-hwmon@...r.kernel.org

with the open question on whether they consider it acceptable for this driver
to be in IIO. Main argument in favour is it's an expensive clinical grade sensor
so fairly unlikely to be used in classic hardware monitoring circumstances.

Anyhow a few comments inline.

Thanks,

Jonathan


> ---
> 
> v4: Version comments go below line separator of signed-off-by
> 
> v3: Release the mutex lock after error gets returned
> 
> v2:
> 1. Removed TODO
> 2. Removed unnecessary blank spaces
> 3. Corrected MC->MILLICELCIUS
> 4. Comments added wherever required
> 5. dev_err on i2c fails
> 6. Rearranged some flows
> 7. Removed PROCESSED
> 8. int error return on gpio setup
> 9. device_register at the end of probe
> 10. Return on unsuccessful reset
> 11. acpi_match_table and of_match_table added
> 12. Minor quirks
> 
> module_i2c_driver() can't be added since module_init and module_exit
> are added explicitly.
> 
>  MAINTAINERS                        |   6 +
>  drivers/iio/temperature/Kconfig    |  10 +
>  drivers/iio/temperature/Makefile   |   1 +
>  drivers/iio/temperature/max30208.c | 322 +++++++++++++++++++++++++++++
>  4 files changed, 339 insertions(+)
>  create mode 100644 drivers/iio/temperature/max30208.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f1390b8270b2..7f1fd2e31b94 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -12373,6 +12373,12 @@ S:	Maintained
>  F:	Documentation/devicetree/bindings/regulator/maxim,max20086.yaml
>  F:	drivers/regulator/max20086-regulator.c
>  
> +MAXIM MAX30208 TEMPERATURE SENSOR DRIVER
> +M:	Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
> +L:	linux-iio@...r.kernel.org
> +S:	Maintained
> +F:	drivers/iio/temperature/max30208.c
> +
>  MAXIM MAX77650 PMIC MFD DRIVER
>  M:	Bartosz Golaszewski <brgl@...ev.pl>
>  L:	linux-kernel@...r.kernel.org
> diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
> index e8ed849e3b76..ed384f33e0c7 100644
> --- a/drivers/iio/temperature/Kconfig
> +++ b/drivers/iio/temperature/Kconfig
> @@ -128,6 +128,16 @@ config TSYS02D
>  	  This driver can also be built as a module. If so, the module will
>  	  be called tsys02d.
>  
> +config MAX30208
> +	tristate "Maxim MAX30208 digital temperature sensor"
> +	depends on I2C
> +	help
> +	  If you say yes here you get support for Maxim MAX30208
> +	  digital temperature sensor connected via I2C.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called max30208.
> +
>  config MAX31856
>  	tristate "MAX31856 thermocouple sensor"
>  	depends on SPI
> diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
> index dd08e562ffe0..dfec8c6d3019 100644
> --- a/drivers/iio/temperature/Makefile
> +++ b/drivers/iio/temperature/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_IQS620AT_TEMP) += iqs620at-temp.o
>  obj-$(CONFIG_LTC2983) += ltc2983.o
>  obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
>  obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
> +obj-$(CONFIG_MAX30208) += max30208.o
>  obj-$(CONFIG_MAX31856) += max31856.o
>  obj-$(CONFIG_MAX31865) += max31865.o
>  obj-$(CONFIG_MLX90614) += mlx90614.o
> diff --git a/drivers/iio/temperature/max30208.c b/drivers/iio/temperature/max30208.c
> new file mode 100644
> index 000000000000..35a778ea9395
> --- /dev/null
> +++ b/drivers/iio/temperature/max30208.c
> @@ -0,0 +1,322 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/*
> + * Copyright (c) Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
> + *
> + * Maxim MAX30208 digital temperature sensor with 0.1°C accuracy
> + * (7-bit I2C slave address (0x50 - 0x53))
> + *
> + * Note: This driver sets GPIO1 to behave as input for temperature
> + * conversion and GPIO0 to act as interrupt for temperature conversion.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/delay.h>
> +#include <linux/iio/iio.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +
> +#define MAX30208_DRV_NAME		"max30208"
> +
> +#define MAX30208_STATUS			0x00
> +#define MAX30208_STATUS_TEMP_RDY	BIT(0)
> +#define MAX30208_INT_ENABLE		0x01
> +#define MAX30208_INT_ENABLE_TEMP_RDY	BIT(0)
> +
> +#define MAX30208_FIFO_OVF_CNTR		0x06
> +#define MAX30208_FIFO_DATA_CNTR		0x07
> +#define MAX30208_FIFO_DATA		0x08
> +
> +#define MAX30208_SYSTEM_CTRL		0x0c
> +#define MAX30208_SYSTEM_CTRL_RESET	0x01
> +
> +#define MAX30208_TEMP_SENSOR_SETUP	0x14
> +#define MAX30208_TEMP_SENSOR_SETUP_CONV	BIT(0)
> +
> +#define MAX30208_GPIO_SETUP		0x20
> +#define MAX30208_GPIO1_SETUP		GENMASK(7, 6)
> +#define MAX30208_GPIO0_SETUP		GENMASK(1, 0)
> +#define MAX30208_GPIO_CTRL		0x21
> +#define MAX30208_GPIO1_CTRL		BIT(3)
> +#define MAX30208_GPIO0_CTRL		BIT(0)
> +
> +#define MAX30208_RES_MILLICELCIUS	5
> +
> +struct max30208_data {
> +	struct i2c_client *client;
> +	struct iio_dev *indio_dev;
> +	struct mutex lock; /* Lock to prevent concurrent reads */
> +};
> +
> +static const struct iio_chan_spec max30208_channels[] = {
> +	{
> +		.type = IIO_TEMP,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +};
> +
> +/**
> + * max30208_request() - Request a reading
> + * @data: Struct comprising member elements of the device
> + *
> + * Requests a reading from the device and waits until the conversion is ready.
> + */
> +static int max30208_request(struct max30208_data *data)
> +{
> +	int retries = 10; /*
> +			   * Sensor can take up to 500 ms to respond so execute a
> +			   * total of 10 retries to give the device sufficient time.
> +			   */

Move the comment to the line above int retries.  Will be more readable there and still
clear what it refers to.

> +	int ret;
> +
> +	ret = i2c_smbus_read_byte_data(data->client, MAX30208_TEMP_SENSOR_SETUP);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error reading reg temperature setup\n");
> +		return ret;
> +	}
> +
> +	ret |= MAX30208_TEMP_SENSOR_SETUP_CONV;
As below, I'd suggest a local u8 variable for building up register values.
> +
> +	ret = i2c_smbus_write_byte_data(data->client, MAX30208_TEMP_SENSOR_SETUP, ret);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error writing reg temperature setup\n");
> +		return ret;
> +	}
> +
> +	while (retries--) {
> +		ret = i2c_smbus_read_byte_data(data->client, MAX30208_STATUS);
> +		if (ret < 0) {
> +			dev_err(&data->client->dev, "Error reading reg status\n");
> +			goto sleep;
> +		}
> +
> +		if (ret & MAX30208_STATUS_TEMP_RDY)
> +			return 0;
> +
> +		msleep(50);
> +	}
> +	dev_warn(&data->client->dev, "Temperature conversion failed\n");
> +
> +	return 0;
> +
> +sleep:
> +	usleep_range(50000, 60000);
> +	return 0;
> +}
> +
> +static int max30208_update_temp(struct max30208_data *data)
> +{
> +	s8 data_count;

It's signed?  That's unusual for a counter...  looking quickly at datasheet
looks like it's actually a 5 bit unsigned counter so this won't matter.
Probably better to use a u8 though to avoid any confusion.


> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +
> +	ret = max30208_request(data);
> +	if (ret < 0)
> +		goto unlock;
> +
> +	ret = i2c_smbus_read_byte_data(data->client, MAX30208_FIFO_OVF_CNTR);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error reading reg FIFO overflow counter\n");
> +		goto unlock;
> +	} else if (!ret) {
> +		ret = i2c_smbus_read_byte_data(data->client,
> +					       MAX30208_FIFO_DATA_CNTR);
> +		if (ret < 0) {
> +			dev_err(&data->client->dev, "Error reading reg FIFO data counter\n");
> +			goto unlock;
> +		}
> +	}
> +
> +	data_count = ret;
> +
> +	/*
> +	 * Ideally, counter should decrease by 1 each time a word is read from FIFO.
> +	 * However, practically, the device behaves erroneously and counter sometimes
> +	 * decreases by more than 1.

This is a very odd hardware bug.  Any public errata reference or similar we can add
here for anyone wanting more information?

>          Hence, do not loop the counter until it becomes 0
> +	 * rather, use the exact counter value after each FIFO word is read.
> +	 * Return the last reading from FIFO as the most recently triggered one.
> +	 */
> +	while (data_count) {
> +		ret = i2c_smbus_read_word_swapped(data->client,
> +						  MAX30208_FIFO_DATA);
> +		if (ret < 0) {
> +			dev_err(&data->client->dev, "Error reading reg FIFO data\n");
> +			goto unlock;
> +		}
> +
> +		data_count = i2c_smbus_read_byte_data(data->client,
> +						      MAX30208_FIFO_DATA_CNTR);
> +		if (data_count < 0) {
> +			dev_err(&data->client->dev, "Error reading reg FIFO data counter\n");
> +			ret = data_count;
> +			goto unlock;
> +		}
> +	}
> +
> +unlock:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +static int max30208_read(struct iio_dev *indio_dev,
> +			 struct iio_chan_spec const *chan,
> +			 int *val, int *val2, long mask)
> +{
> +	struct max30208_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = max30208_update_temp(data);
> +		if (ret < 0)
> +			return ret;
> +
> +		*val = sign_extend32(ret, 15);
> +		return IIO_VAL_INT;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = MAX30208_RES_MILLICELCIUS;

Given this define is only used in one place + isn't a magic value (it is the actual
resolution!) I'd prefer to see the number directly here.

> +		return IIO_VAL_INT;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int max30208_gpio_setup(struct max30208_data *data)
> +{
> +	int ret;
> +
> +	ret = i2c_smbus_read_byte_data(data->client,
> +				       MAX30208_GPIO_SETUP);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error reading reg GPIO setup\n");
> +		return ret;
> +	}
> +
> +	/*
> +	 * Setting GPIO1 to trigger temperature conversion
> +	 * when driven low.
> +	 * Setting GPIO0 to trigger interrupt when temperature
> +	 * conversion gets completed.
> +	 */
> +	ret |= MAX30208_GPIO1_SETUP | MAX30208_GPIO0_SETUP;
It is cleaner to use a local u8 variable to build up the register value rather than
using the integer that is returned directly. 

	u8 regval;

	regval = 
	regval = ret | ....

	... write_byte_data(..., regval);

etc as it keeps the types involved clean and makes it clear to a compiler that
we are deliberately truncating the return value etc.


> +	ret = i2c_smbus_write_byte_data(data->client,
> +					MAX30208_GPIO_SETUP, ret);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error writing reg GPIO setup\n");
> +		return ret;
> +	}
> +
> +	ret = i2c_smbus_read_byte_data(data->client,
> +				       MAX30208_INT_ENABLE);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error reading reg interrupt enable\n");
> +		return ret;
> +	}
> +
> +	/* Enabling GPIO0 interrupt */
> +	ret |= MAX30208_INT_ENABLE_TEMP_RDY;
> +	ret = i2c_smbus_write_byte_data(data->client,
> +					MAX30208_INT_ENABLE, ret);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "Error writing reg interrupt enable\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct iio_info max30208_info = {
> +	.read_raw = max30208_read,
> +};
> +
> +static int max30208_probe(struct i2c_client *i2c)
> +{
> +	struct device *dev = &i2c->dev;
> +	struct max30208_data *data;
> +	struct iio_dev *indio_dev;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->client = i2c;
> +	mutex_init(&data->lock);
> +
> +	indio_dev->name = MAX30208_DRV_NAME;
> +	indio_dev->channels = max30208_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max30208_channels);
> +	indio_dev->info = &max30208_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +
> +	/* Reset the device initially */
> +	ret = i2c_smbus_write_byte_data(data->client, MAX30208_SYSTEM_CTRL,
> +					MAX30208_SYSTEM_CTRL_RESET);
> +	if (ret) {
> +		dev_err(dev, "Failure in performing reset\n");
> +		return ret;
> +	}
> +
> +	usleep_range(50000, 60000);
> +
> +	ret = max30208_gpio_setup(data);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret) {
> +		dev_err(dev, "Failed to register IIO device\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id max30208_id_table[] = {
> +	{ "max30208" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(i2c, max30208_id_table);
> +
> +static const struct acpi_device_id max30208_acpi_match[] = {
> +	{ "MAX30208" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(acpi, max30208_acpi_match);
> +
> +static const struct of_device_id max30208_of_match[] = {
> +	{ .compatible = "maxim,max30208" },
> +	{ },

No need for comma on 'NULL' terminators.  We won't ever add another entry
after then so it is good to make it harder to do that acccidentally.
	{ }
};

> +};
> +MODULE_DEVICE_TABLE(of, max30208_of_match);
> +
> +static struct i2c_driver max30208_driver = {
> +	.driver = {
> +		.name = MAX30208_DRV_NAME,
> +		.of_match_table = max30208_of_match,
> +		.acpi_match_table = ACPI_PTR(max30208_acpi_match),

As per the build warning, don't bother with ACPI_PTR().
It saves a tiny bit on the size of the driver, but at the cost of needing
to use ifdef or __maybe_unused.  Now if someone made that work in a similar
fashion to pm_ptr() that doesn't suffer this problem then I'd be happier seeing
it in drivers. 

> +	},
> +	.probe_new = max30208_probe,
> +	.id_table = max30208_id_table,
> +};
> +
> +static int __init max30208_init(void)
> +{
> +	return i2c_add_driver(&max30208_driver);
> +}
> +module_init(max30208_init);
> +
> +static void __exit max30208_exit(void)
> +{
> +	i2c_del_driver(&max30208_driver);
> +}
> +module_exit(max30208_exit);
> +
> +MODULE_AUTHOR("Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>");
> +MODULE_DESCRIPTION("Maxim MAX30208 digital temperature sensor");
> +MODULE_LICENSE("GPL");

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