Re: [PATCH 08/10] hwmon: (max197) Remove driver

["Nuno Sá" <nuno.sa@analog.com>]

On Tue, Nov 10, 2026 at 10:34:31AM -0800, Guenter Roeck wrote:
> The max197 driver requires platform data providing a convert() callback
> function pointer and fails to probe without it. No in-tree platform ever
> instantiates max197 or supplies struct max197_platform_data, and there
> is no alternative mechanism to access the chip.
> 
> Remove the unused driver, its platform_data header file, Kconfig/Makefile
> entries, and documentation.
> 
> Cc: Nuno Sá <nuno.sa@analog.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---

This one is still in production but looking at it I agree it would be
not so straight to make this driver usable. Hence,

Reviewed-by: Nuno Sá <nuno.sa@analog.com>

>  Documentation/hwmon/index.rst        |   1 -
>  Documentation/hwmon/max197.rst       |  70 ------
>  drivers/hwmon/Kconfig                |   9 -
>  drivers/hwmon/Makefile               |   1 -
>  drivers/hwmon/max197.c               | 341 ---------------------------
>  include/linux/platform_data/max197.h |  23 --
>  6 files changed, 445 deletions(-)
>  delete mode 100644 Documentation/hwmon/max197.rst
>  delete mode 100644 drivers/hwmon/max197.c
>  delete mode 100644 include/linux/platform_data/max197.h
> 
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index 7ce1a6f42ddc..e364e051457f 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -168,7 +168,6 @@ Hardware Monitoring Kernel Drivers
>     max16601
>     max1668
>     max17616
> -   max197
>     max20730
>     max20751
>     max20826
> diff --git a/Documentation/hwmon/max197.rst b/Documentation/hwmon/max197.rst
> deleted file mode 100644
> index 00e16056823f..000000000000
> --- a/Documentation/hwmon/max197.rst
> +++ /dev/null
> @@ -1,70 +0,0 @@
> -Kernel driver max197
> -====================
> -
> -Author:
> -
> -  * Vivien Didelot <vivien.didelot@savoirfairelinux.com>
> -
> -Supported chips:
> -
> -  * Maxim MAX197
> -
> -    Prefix: 'max197'
> -
> -    Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX197.pdf
> -
> -  * Maxim MAX199
> -
> -    Prefix: 'max199'
> -
> -    Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX199.pdf
> -
> -Description
> ------------
> -
> -The A/D converters MAX197, and MAX199 are both 8-Channel, Multi-Range, 5V,
> -12-Bit DAS with 8+4 Bus Interface and Fault Protection.
> -
> -The available ranges for the MAX197 are {0,-5V} to 5V, and {0,-10V} to 10V,
> -while they are {0,-2V} to 2V, and {0,-4V} to 4V on the MAX199.
> -
> -Platform data
> --------------
> -
> -The MAX197 platform data (defined in linux/platform_data/max197.h) should be
> -filled with a pointer to a conversion function, defined like::
> -
> -    int convert(u8 ctrl);
> -
> -ctrl is the control byte to write to start a new conversion.
> -On success, the function must return the 12-bit raw value read from the chip,
> -or a negative error code otherwise.
> -
> -Control byte format:
> -
> -======= ========== ============================================
> -Bit     Name       Description
> -7,6     PD1,PD0    Clock and Power-Down modes
> -5       ACQMOD     Internal or External Controlled Acquisition
> -4       RNG        Full-scale voltage magnitude at the input
> -3       BIP        Unipolar or Bipolar conversion mode
> -2,1,0   A2,A1,A0   Channel
> -======= ========== ============================================
> -
> -Sysfs interface
> ----------------
> -
> -  ============== ==============================================================
> -  in[0-7]_input  The conversion value for the corresponding channel.
> -		 RO
> -
> -  in[0-7]_min    The lower limit (in mV) for the corresponding channel.
> -		 For the MAX197, it will be adjusted to -10000, -5000, or 0.
> -		 For the MAX199, it will be adjusted to -4000, -2000, or 0.
> -		 RW
> -
> -  in[0-7]_max    The higher limit (in mV) for the corresponding channel.
> -		 For the MAX197, it will be adjusted to 0, 5000, or 10000.
> -		 For the MAX199, it will be adjusted to 0, 2000, or 4000.
> -		 RW
> -  ============== ==============================================================
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 9979958a59a2..1612a408c287 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1342,15 +1342,6 @@ config SENSORS_MAX1668
>  	  This driver can also be built as a module. If so, the module
>  	  will be called max1668.
>  
> -config SENSORS_MAX197
> -	tristate "Maxim MAX197 and compatibles"
> -	help
> -	  Support for the Maxim MAX197 A/D converter.
> -	  Support will include, but not be limited to, MAX197, and MAX199.
> -
> -	  This driver can also be built as a module. If so, the module
> -	  will be called max197.
> -
>  config SENSORS_MAX31722
>  	tristate "MAX31722 temperature sensor"
>  	depends on SPI
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index ec4b0de8cf47..56776df17cfd 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -164,7 +164,6 @@ obj-$(CONFIG_SENSORS_MAX127)	+= max127.o
>  obj-$(CONFIG_SENSORS_MAX16065)	+= max16065.o
>  obj-$(CONFIG_SENSORS_MAX1619)	+= max1619.o
>  obj-$(CONFIG_SENSORS_MAX1668)	+= max1668.o
> -obj-$(CONFIG_SENSORS_MAX197)	+= max197.o
>  obj-$(CONFIG_SENSORS_MAX31722)	+= max31722.o
>  obj-$(CONFIG_SENSORS_MAX31730)	+= max31730.o
>  obj-$(CONFIG_SENSORS_MAX31760)  += max31760.o
> diff --git a/drivers/hwmon/max197.c b/drivers/hwmon/max197.c
> deleted file mode 100644
> index a613abfdc2db..000000000000
> --- a/drivers/hwmon/max197.c
> +++ /dev/null
> @@ -1,341 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -/*
> - * Maxim MAX197 A/D Converter driver
> - *
> - * Copyright (c) 2012 Savoir-faire Linux Inc.
> - *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>
> - *
> - * For further information, see the Documentation/hwmon/max197.rst file.
> - */
> -
> -#include <linux/kernel.h>
> -#include <linux/module.h>
> -#include <linux/init.h>
> -#include <linux/err.h>
> -#include <linux/slab.h>
> -#include <linux/mutex.h>
> -#include <linux/device.h>
> -#include <linux/sysfs.h>
> -#include <linux/hwmon.h>
> -#include <linux/hwmon-sysfs.h>
> -#include <linux/platform_device.h>
> -#include <linux/platform_data/max197.h>
> -
> -#define MAX199_LIMIT	4000		/* 4V */
> -#define MAX197_LIMIT	10000		/* 10V */
> -
> -#define MAX197_NUM_CH	8		/* 8 Analog Input Channels */
> -
> -/* Control byte format */
> -#define MAX197_BIP	(1 << 3)	/* Bipolarity */
> -#define MAX197_RNG	(1 << 4)	/* Full range */
> -
> -#define MAX197_SCALE	12207		/* Scale coefficient for raw data */
> -
> -/* List of supported chips */
> -enum max197_chips { max197, max199 };
> -
> -/**
> - * struct max197_data - device instance specific data
> - * @pdata:		Platform data.
> - * @hwmon_dev:		The hwmon device.
> - * @lock:		Read/Write mutex.
> - * @limit:		Max range value (10V for MAX197, 4V for MAX199).
> - * @scale:		Need to scale.
> - * @ctrl_bytes:		Channels control byte.
> - */
> -struct max197_data {
> -	struct max197_platform_data *pdata;
> -	struct device *hwmon_dev;
> -	struct mutex lock;
> -	int limit;
> -	bool scale;
> -	u8 ctrl_bytes[MAX197_NUM_CH];
> -};
> -
> -static inline void max197_set_unipolarity(struct max197_data *data, int channel)
> -{
> -	data->ctrl_bytes[channel] &= ~MAX197_BIP;
> -}
> -
> -static inline void max197_set_bipolarity(struct max197_data *data, int channel)
> -{
> -	data->ctrl_bytes[channel] |= MAX197_BIP;
> -}
> -
> -static inline void max197_set_half_range(struct max197_data *data, int channel)
> -{
> -	data->ctrl_bytes[channel] &= ~MAX197_RNG;
> -}
> -
> -static inline void max197_set_full_range(struct max197_data *data, int channel)
> -{
> -	data->ctrl_bytes[channel] |= MAX197_RNG;
> -}
> -
> -static inline bool max197_is_bipolar(struct max197_data *data, int channel)
> -{
> -	return data->ctrl_bytes[channel] & MAX197_BIP;
> -}
> -
> -static inline bool max197_is_full_range(struct max197_data *data, int channel)
> -{
> -	return data->ctrl_bytes[channel] & MAX197_RNG;
> -}
> -
> -/* Function called on read access on in{0,1,2,3,4,5,6,7}_{min,max} */
> -static ssize_t max197_show_range(struct device *dev,
> -				 struct device_attribute *devattr, char *buf)
> -{
> -	struct max197_data *data = dev_get_drvdata(dev);
> -	struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(devattr);
> -	int channel = attr->index;
> -	bool is_min = attr->nr;
> -	int range;
> -
> -	if (mutex_lock_interruptible(&data->lock))
> -		return -ERESTARTSYS;
> -
> -	range = max197_is_full_range(data, channel) ?
> -		data->limit : data->limit / 2;
> -	if (is_min) {
> -		if (max197_is_bipolar(data, channel))
> -			range = -range;
> -		else
> -			range = 0;
> -	}
> -
> -	mutex_unlock(&data->lock);
> -
> -	return sprintf(buf, "%d\n", range);
> -}
> -
> -/* Function called on write access on in{0,1,2,3,4,5,6,7}_{min,max} */
> -static ssize_t max197_store_range(struct device *dev,
> -				  struct device_attribute *devattr,
> -				  const char *buf, size_t count)
> -{
> -	struct max197_data *data = dev_get_drvdata(dev);
> -	struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(devattr);
> -	int channel = attr->index;
> -	bool is_min = attr->nr;
> -	long value;
> -	int half = data->limit / 2;
> -	int full = data->limit;
> -
> -	if (kstrtol(buf, 10, &value))
> -		return -EINVAL;
> -
> -	if (is_min) {
> -		if (value <= -full)
> -			value = -full;
> -		else if (value < 0)
> -			value = -half;
> -		else
> -			value = 0;
> -	} else {
> -		if (value >= full)
> -			value = full;
> -		else
> -			value = half;
> -	}
> -
> -	if (mutex_lock_interruptible(&data->lock))
> -		return -ERESTARTSYS;
> -
> -	if (value == 0) {
> -		/* We can deduce only the polarity */
> -		max197_set_unipolarity(data, channel);
> -	} else if (value == -half) {
> -		max197_set_bipolarity(data, channel);
> -		max197_set_half_range(data, channel);
> -	} else if (value == -full) {
> -		max197_set_bipolarity(data, channel);
> -		max197_set_full_range(data, channel);
> -	} else if (value == half) {
> -		/* We can deduce only the range */
> -		max197_set_half_range(data, channel);
> -	} else if (value == full) {
> -		/* We can deduce only the range */
> -		max197_set_full_range(data, channel);
> -	}
> -
> -	mutex_unlock(&data->lock);
> -
> -	return count;
> -}
> -
> -/* Function called on read access on in{0,1,2,3,4,5,6,7}_input */
> -static ssize_t max197_show_input(struct device *dev,
> -				 struct device_attribute *devattr,
> -				 char *buf)
> -{
> -	struct max197_data *data = dev_get_drvdata(dev);
> -	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
> -	int channel = attr->index;
> -	s32 value;
> -	int ret;
> -
> -	if (mutex_lock_interruptible(&data->lock))
> -		return -ERESTARTSYS;
> -
> -	ret = data->pdata->convert(data->ctrl_bytes[channel]);
> -	if (ret < 0) {
> -		dev_err(dev, "conversion failed\n");
> -		goto unlock;
> -	}
> -	value = ret;
> -
> -	/*
> -	 * Coefficient to apply on raw value.
> -	 * See Table 1. Full Scale and Zero Scale in the MAX197 datasheet.
> -	 */
> -	if (data->scale) {
> -		value *= MAX197_SCALE;
> -		if (max197_is_full_range(data, channel))
> -			value *= 2;
> -		value /= 10000;
> -	}
> -
> -	ret = sprintf(buf, "%d\n", value);
> -
> -unlock:
> -	mutex_unlock(&data->lock);
> -	return ret;
> -}
> -
> -static ssize_t name_show(struct device *dev, struct device_attribute *attr,
> -			 char *buf)
> -{
> -	struct platform_device *pdev = to_platform_device(dev);
> -	return sprintf(buf, "%s\n", pdev->name);
> -}
> -
> -#define MAX197_SENSOR_DEVICE_ATTR_CH(chan)				\
> -	static SENSOR_DEVICE_ATTR(in##chan##_input, S_IRUGO,		\
> -				  max197_show_input, NULL, chan);	\
> -	static SENSOR_DEVICE_ATTR_2(in##chan##_min, S_IRUGO | S_IWUSR,	\
> -				    max197_show_range,			\
> -				    max197_store_range,			\
> -				    true, chan);			\
> -	static SENSOR_DEVICE_ATTR_2(in##chan##_max, S_IRUGO | S_IWUSR,	\
> -				    max197_show_range,			\
> -				    max197_store_range,			\
> -				    false, chan)
> -
> -#define MAX197_SENSOR_DEV_ATTR_IN(chan)					\
> -	&sensor_dev_attr_in##chan##_input.dev_attr.attr,		\
> -	&sensor_dev_attr_in##chan##_max.dev_attr.attr,			\
> -	&sensor_dev_attr_in##chan##_min.dev_attr.attr
> -
> -static DEVICE_ATTR_RO(name);
> -
> -MAX197_SENSOR_DEVICE_ATTR_CH(0);
> -MAX197_SENSOR_DEVICE_ATTR_CH(1);
> -MAX197_SENSOR_DEVICE_ATTR_CH(2);
> -MAX197_SENSOR_DEVICE_ATTR_CH(3);
> -MAX197_SENSOR_DEVICE_ATTR_CH(4);
> -MAX197_SENSOR_DEVICE_ATTR_CH(5);
> -MAX197_SENSOR_DEVICE_ATTR_CH(6);
> -MAX197_SENSOR_DEVICE_ATTR_CH(7);
> -
> -static const struct attribute_group max197_sysfs_group = {
> -	.attrs = (struct attribute *[]) {
> -		&dev_attr_name.attr,
> -		MAX197_SENSOR_DEV_ATTR_IN(0),
> -		MAX197_SENSOR_DEV_ATTR_IN(1),
> -		MAX197_SENSOR_DEV_ATTR_IN(2),
> -		MAX197_SENSOR_DEV_ATTR_IN(3),
> -		MAX197_SENSOR_DEV_ATTR_IN(4),
> -		MAX197_SENSOR_DEV_ATTR_IN(5),
> -		MAX197_SENSOR_DEV_ATTR_IN(6),
> -		MAX197_SENSOR_DEV_ATTR_IN(7),
> -		NULL
> -	},
> -};
> -
> -static int max197_probe(struct platform_device *pdev)
> -{
> -	int ch, ret;
> -	struct max197_data *data;
> -	struct max197_platform_data *pdata = dev_get_platdata(&pdev->dev);
> -	enum max197_chips chip = platform_get_device_id(pdev)->driver_data;
> -
> -	if (pdata == NULL) {
> -		dev_err(&pdev->dev, "no platform data supplied\n");
> -		return -EINVAL;
> -	}
> -
> -	if (pdata->convert == NULL) {
> -		dev_err(&pdev->dev, "no convert function supplied\n");
> -		return -EINVAL;
> -	}
> -
> -	data = devm_kzalloc_obj(&pdev->dev, struct max197_data);
> -	if (!data)
> -		return -ENOMEM;
> -
> -	data->pdata = pdata;
> -	mutex_init(&data->lock);
> -
> -	if (chip == max197) {
> -		data->limit = MAX197_LIMIT;
> -		data->scale = true;
> -	} else {
> -		data->limit = MAX199_LIMIT;
> -		data->scale = false;
> -	}
> -
> -	for (ch = 0; ch < MAX197_NUM_CH; ch++)
> -		data->ctrl_bytes[ch] = (u8) ch;
> -
> -	platform_set_drvdata(pdev, data);
> -
> -	ret = sysfs_create_group(&pdev->dev.kobj, &max197_sysfs_group);
> -	if (ret) {
> -		dev_err(&pdev->dev, "sysfs create group failed\n");
> -		return ret;
> -	}
> -
> -	data->hwmon_dev = hwmon_device_register(&pdev->dev);
> -	if (IS_ERR(data->hwmon_dev)) {
> -		ret = PTR_ERR(data->hwmon_dev);
> -		dev_err(&pdev->dev, "hwmon device register failed\n");
> -		goto error;
> -	}
> -
> -	return 0;
> -
> -error:
> -	sysfs_remove_group(&pdev->dev.kobj, &max197_sysfs_group);
> -	return ret;
> -}
> -
> -static void max197_remove(struct platform_device *pdev)
> -{
> -	struct max197_data *data = platform_get_drvdata(pdev);
> -
> -	hwmon_device_unregister(data->hwmon_dev);
> -	sysfs_remove_group(&pdev->dev.kobj, &max197_sysfs_group);
> -}
> -
> -static const struct platform_device_id max197_device_ids[] = {
> -	{ .name = "max197", .driver_data = max197 },
> -	{ .name = "max199", .driver_data = max199 },
> -	{ }
> -};
> -MODULE_DEVICE_TABLE(platform, max197_device_ids);
> -
> -static struct platform_driver max197_driver = {
> -	.driver = {
> -		.name = "max197",
> -	},
> -	.probe = max197_probe,
> -	.remove = max197_remove,
> -	.id_table = max197_device_ids,
> -};
> -module_platform_driver(max197_driver);
> -
> -MODULE_LICENSE("GPL");
> -MODULE_AUTHOR("Savoir-faire Linux Inc. <kernel@savoirfairelinux.com>");
> -MODULE_DESCRIPTION("Maxim MAX197 A/D Converter driver");
> diff --git a/include/linux/platform_data/max197.h b/include/linux/platform_data/max197.h
> deleted file mode 100644
> index 03ef46f9cd65..000000000000
> --- a/include/linux/platform_data/max197.h
> +++ /dev/null
> @@ -1,23 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-only */
> -/*
> - * Maxim MAX197 A/D Converter Driver
> - *
> - * Copyright (c) 2012 Savoir-faire Linux Inc.
> - *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>
> - *
> - * For further information, see the Documentation/hwmon/max197.rst file.
> - */
> -
> -#ifndef _PDATA_MAX197_H
> -#define _PDATA_MAX197_H
> -
> -/**
> - * struct max197_platform_data - MAX197 connectivity info
> - * @convert:	Function used to start a conversion with control byte ctrl.
> - *		It must return the raw data, or a negative error code.
> - */
> -struct max197_platform_data {
> -	int (*convert)(u8 ctrl);
> -};
> -
> -#endif /* _PDATA_MAX197_H */
> -- 
> 2.45.2
>