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Date:   Wed, 26 Apr 2023 07:57:08 -0700
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To:     Daniel Matyas <daniel.matyas@analog.com>
Cc:     Jean Delvare <jdelvare@suse.com>, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jonathan Corbet <corbet@lwn.net>, linux-hwmon@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org
References: <20230426124049.258359-1-daniel.matyas@analog.com>
 <20230426124049.258359-2-daniel.matyas@analog.com>
 <20230426124049.258359-3-daniel.matyas@analog.com>
From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v3 2/2] hwmon: max31827: add MAX31827 driver
In-Reply-To: <20230426124049.258359-3-daniel.matyas@analog.com>
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On 4/26/23 05:40, Daniel Matyas wrote:
> MAX31827 is a low-power temperature switch with I2C interface.
> 
> The device is a ±1°C accuracy from -40°C to +125°C
> (12 bits) local temperature switch and sensor with I2C/SM-
> Bus interface. The combination of small 6-bump wafer-lev-
> el package (WLP) and high accuracy makes this temper-
> ature sensor/switch ideal for a wide range of applications.
> 
> Signed-off-by: Daniel Matyas <daniel.matyas@analog.com>
> ---
>   Documentation/hwmon/index.rst    |   1 +
>   Documentation/hwmon/max31827.rst |  83 +++++++
>   MAINTAINERS                      |   2 +
>   drivers/hwmon/Kconfig            |  11 +
>   drivers/hwmon/Makefile           |   2 +-
>   drivers/hwmon/max31827.c         | 406 +++++++++++++++++++++++++++++++
>   6 files changed, 504 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/hwmon/max31827.rst
>   create mode 100644 drivers/hwmon/max31827.c
> 
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index f1fe75f596a5..965a830ea766 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -139,6 +139,7 @@ Hardware Monitoring Kernel Drivers
>      max31760
>      max31785
>      max31790
> +   max31827
>      max34440
>      max6620
>      max6639
> diff --git a/Documentation/hwmon/max31827.rst b/Documentation/hwmon/max31827.rst
> new file mode 100644
> index 000000000000..5b94ad62baa3
> --- /dev/null
> +++ b/Documentation/hwmon/max31827.rst
> @@ -0,0 +1,83 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Kernel driver max31827
> +======================
> +
> +Supported chips:
> +
> +  * Maxim MAX31827
> +
> +    Prefix: 'max31827'
> +
> +    Addresses scanned: I2C 0x40 - 0x5f
> +
> +    Datasheet: Publicly available at the Analog Devices website
> +
> +  * Maxim MAX31828
> +
> +    Prefix: 'max31828'
> +
> +    Addresses scanned: I2C 0x40 - 0x5f
> +
> +    Datasheet: Publicly available at the Analog Devices website
> +
> +  * Maxim MAX31829
> +
> +    Prefix: 'max31829'
> +
> +    Addresses scanned: I2C 0x40 - 0x5f
> +
> +    Datasheet: Publicly available at the Analog Devices website
> +
> +
> +Authors:
> +	- Daniel Matyas <daniel.matyas@analog.com>
> +
> +Description
> +-----------
> +
> +The chips supported by this driver are quite similar. The only difference
> +between them is found in the default power-on behaviour of the chips. While the
> +MAX31827's fault queue is set to 1, the other two chip's fault queue is set to
> +4. Besides this, the MAX31829's alarm active state is high, while the other two
> +chip's alarms are active on low. It is important to note that the chips can be
> +configured to operate in the same manner with 1 write operation to the
> +configuration register. From here on, we will refer to all these chips as
> +MAX31827.
> +
> +MAX31827 implements a temperature sensor with a 6 WLP packaging scheme. This
> +sensor measures the temperature of the chip itself.
> +
> +MAX31827 has low and over temperature alarms with an effective value and a
> +hysteresis value: -40 and -30 degrees for under temperature alarm and +100 and
> ++90 degrees for over temperature alarm.
> +
> +The alarm can be configured in comparator and interrupt mode. Currently only
> +comparator mode is implemented. In Comparator mode, the OT/UT status bits have a
> +value of 1 when the temperature rises above the TH value or falls below TL,
> +which is also subject to the Fault Queue selection. OT status returns to 0 when
> +the temperature drops below the TH_HYST value or when shutdown mode is entered.
> +Similarly, UT status returns to 0 when the temperature rises above TL_HYST value
> +or when shutdown mode is entered.
> +
> +Putting the MAX31827 into shutdown mode also resets the OT/UT status bits. Note
> +that if the mode is changed while OT/UT status bits are set, an OT/UT status
> +reset may be required before it begins to behave normally. To prevent this,
> +it is recommended to perform a read of the configuration/status register to
> +clear the status bits before changing the operating mode.
> +
> +The conversions can be manual with the one-shot functionality and automatic with
> +a set frequency. When powered on, the chip measures temperatures with 1 conv/s.
> +Enabling the device when it is already enabled has the side effect of setting
> +the conversion frequency to 1 conv/s. The conversion time varies depending on
> +the resolution. The conversion time doubles with every bit of increased
> +resolution. For 10 bit resolution 35ms are needed, while for 12 bit resolution
> +(default) 140ms. When chip is in shutdown mode and a read operation is
> +requested, one-shot is triggered, the device waits for 140 (conversion time) + 1
> +(error) ms, and only after that is the temperature value register read.
> +
> +Notes
> +-----
> +
> +Currently fault queue, alarm polarity and resolution cannot be modified.
> +PEC is not implemented either.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0997a0490c97..fabc8869b13b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -12541,6 +12541,8 @@ L:	linux-hwmon@vger.kernel.org
>   S:	Supported
>   W:	http://ez.analog.com/community/linux-device-drivers
>   F:	Documentation/devicetree/bindings/hwmon/adi,max31827.yaml
> +F:	Documentation/hwmon/max31827.rst
> +F:	drivers/hwmon/max31827.c
>   
>   MAX6650 HARDWARE MONITOR AND FAN CONTROLLER DRIVER
>   L:	linux-hwmon@vger.kernel.org
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 5b3b76477b0e..1e8546b3a8f2 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1097,6 +1097,17 @@ config SENSORS_MAX31760
>   	  This driver can also be built as a module. If so, the module
>   	  will be called max31760.
>   
> +config MAX31827
> +	tristate "MAX31827 low-power temperature switch and similar devices"
> +	depends on I2C
> +	select REGMAP_I2C
> +	help
> +	  If you say yes here you get support for MAX31827, MAX31828 and
> +	  MAX31829 low-power temperature switches and sensors connected with I2C.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called max31827.
> +
>   config SENSORS_MAX6620
>   	tristate "Maxim MAX6620 fan controller"
>   	depends on I2C
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 88712b5031c8..dfb9aaf979bb 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -149,6 +149,7 @@ obj-$(CONFIG_SENSORS_MAX6642)	+= max6642.o
>   obj-$(CONFIG_SENSORS_MAX6650)	+= max6650.o
>   obj-$(CONFIG_SENSORS_MAX6697)	+= max6697.o
>   obj-$(CONFIG_SENSORS_MAX31790)	+= max31790.o
> +obj-$(CONFIG_MAX31827) += max31827.o
>   obj-$(CONFIG_SENSORS_MC13783_ADC)+= mc13783-adc.o
>   obj-$(CONFIG_SENSORS_MC34VR500)	+= mc34vr500.o
>   obj-$(CONFIG_SENSORS_MCP3021)	+= mcp3021.o
> @@ -223,4 +224,3 @@ obj-$(CONFIG_SENSORS_PECI)	+= peci/
>   obj-$(CONFIG_PMBUS)		+= pmbus/
>   
>   ccflags-$(CONFIG_HWMON_DEBUG_CHIP) := -DDEBUG
> -
> diff --git a/drivers/hwmon/max31827.c b/drivers/hwmon/max31827.c
> new file mode 100644
> index 000000000000..ed8ab9c9abb9
> --- /dev/null
> +++ b/drivers/hwmon/max31827.c
> @@ -0,0 +1,406 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * max31827.c - Support for Maxim Low-Power Switch
> + *
> + * Copyright (c) 2023 Daniel Matyas <daniel.matyas@analog.com>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/delay.h>
> +#include <linux/hwmon.h>
> +#include <linux/i2c.h>
> +#include <linux/mutex.h>
> +#include <linux/regmap.h>
> +
> +#define MAX31827_T_REG	0x0
> +#define MAX31827_CONFIGURATION_REG	0x2
> +#define MAX31827_TH_REG	0x4
> +#define MAX31827_TL_REG 0x6
> +#define MAX31827_TH_HYST_REG	0x8
> +#define MAX31827_TL_HYST_REG	0xA
> +
> +#define MAX31827_CONFIGURATION_1SHOT_MASK	BIT(0)
> +#define MAX31827_CONFIGURATION_CNV_RATE_MASK	GENMASK(3, 1)
> +#define MAX31827_CONFIGURATION_U_TEMP_STAT_MASK BIT(14)
> +#define MAX31827_CONFIGURATION_O_TEMP_STAT_MASK BIT(15)
> +
> +#define MAX31827_12_BIT_CNV_TIME	141
> +
> +#define MAX31827_CNV_1_DIV_64_HZ	0x1
> +#define MAX31827_CNV_1_DIV_32_HZ	0x2
> +#define MAX31827_CNV_1_DIV_16_HZ	0x3
> +#define MAX31827_CNV_1_DIV_4_HZ		0x4
> +#define MAX31827_CNV_1_HZ	0x5
> +#define MAX31827_CNV_4_HZ	0x6
> +#define MAX31827_CNV_8_HZ	0x7
> +
> +#define MAX31827_DEVICE_ENABLE(x) ((x) ? 0xA : 0x0)
> +
> +struct max31827_state {
> +	/*
> +	 * Prevent simultaneous access to the i2c client.
> +	 */
> +	struct mutex lock;
> +	struct regmap *regmap;
> +	bool enable;
> +};
> +
> +static const struct regmap_config max31827_regmap = {
> +	.reg_bits = 8,
> +	.val_bits = 16,
> +	.max_register = 0xA,
> +};
> +
> +static int write_alarm_val(struct max31827_state *st, unsigned int reg,
> +			   long val)
> +{
> +	unsigned int cfg;
> +	unsigned int tmp;
> +	int ret;
> +
> +	/*
> +	 * Before the Temperature Threshold Alarm and Alarm Hysteresis Threshold
> +	 * register values are changed over I2C, the part must be in shutdown
> +	 * mode.
> +	 *
> +	 * Mutex is used to ensure, that some other process doesn't change the
> +	 * configuration register.
> +	 */
> +
> +	if (!st->enable)
> +		return regmap_write(st->regmap, reg, val);
> +
As mentioned above, this check needs to be mutex protected.

> +	mutex_lock(&st->lock);
> +
> +	ret = regmap_read(st->regmap, MAX31827_CONFIGURATION_REG, &cfg);
> +	if (ret)
> +		return ret;
> +
> +	tmp = cfg & ~(MAX31827_CONFIGURATION_1SHOT_MASK |
> +		      MAX31827_CONFIGURATION_CNV_RATE_MASK);
> +	ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, tmp);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(st->regmap, reg, val);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, cfg);
> +
> +	mutex_unlock(&st->lock);
> +
> +	return ret;
> +}
> +
> +static umode_t max31827_is_visible(const void *state,
> +				   enum hwmon_sensor_types type, u32 attr,
> +				   int channel)
> +{
> +	if (type == hwmon_temp) {
> +		switch (attr) {
> +		case hwmon_temp_enable:
> +		case hwmon_temp_max:
> +		case hwmon_temp_min:
> +		case hwmon_temp_max_hyst:
> +		case hwmon_temp_min_hyst:
> +			return 0644;
> +		case hwmon_temp_input:
> +		case hwmon_temp_min_alarm:
> +		case hwmon_temp_max_alarm:
> +			return 0444;

Missing default:

> +		}
> +	} else if (type == hwmon_chip) {
> +		if (attr == hwmon_chip_update_interval)
> +			return 0644;
> +	}
> +
> +	return 0;
> +}
> +
> +static int max31827_read(struct device *dev, enum hwmon_sensor_types type,
> +			 u32 attr, int channel, long *val)
> +{
> +	struct max31827_state *st = dev_get_drvdata(dev);
> +	unsigned int uval;
> +	int ret;
> +
> +	switch (type) {
> +	case hwmon_temp:
> +		switch (attr) {
> +		case hwmon_temp_enable:
> +			ret = regmap_read(st->regmap,
> +					  MAX31827_CONFIGURATION_REG, &uval);
> +			uval = FIELD_GET(MAX31827_CONFIGURATION_1SHOT_MASK |
> +					 MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +				uval);
> +			uval = !!uval;
> +
> +			break;
> +		case hwmon_temp_input:
> +			if (!st->enable) {

All accesses to st->enable must be mutex protected since the value could otherwise
change while the rest of the code executes. That includes accesses to temperature
registers because the chip could otherwise be disabled just before temperature
registers are read.

> +				/*
> +				 * This operation requires mutex protection,
> +				 * because the chip configuration should not
> +				 * be changed during the conversion process.
> +				 */
> +
> +				mutex_lock(&st->lock);
> +
> +				ret = regmap_update_bits(st->regmap,
> +							 MAX31827_CONFIGURATION_REG,
> +							 MAX31827_CONFIGURATION_1SHOT_MASK,
> +							 1);
> +				if (ret)
> +					return ret;
> +
> +				msleep(MAX31827_12_BIT_CNV_TIME);
> +
> +				mutex_unlock(&st->lock);
> +			}
> +			ret = regmap_read(st->regmap, MAX31827_T_REG, &uval);
> +
> +			break;
> +		case hwmon_temp_max:
> +			ret = regmap_read(st->regmap, MAX31827_TH_REG, &uval);
> +			break;
> +		case hwmon_temp_max_hyst:
> +			ret = regmap_read(st->regmap, MAX31827_TH_HYST_REG,
> +					  &uval);
> +			break;
> +		case hwmon_temp_max_alarm:
> +			ret = regmap_read(st->regmap,
> +					  MAX31827_CONFIGURATION_REG, &uval);
> +			uval = FIELD_GET(MAX31827_CONFIGURATION_O_TEMP_STAT_MASK,
> +					 uval);
> +			break;
> +		case hwmon_temp_min:
> +			ret = regmap_read(st->regmap, MAX31827_TL_REG, &uval);
> +			break;
> +		case hwmon_temp_min_hyst:
> +			ret = regmap_read(st->regmap, MAX31827_TL_HYST_REG,
> +					  &uval);
> +			break;

Conversion to milli-degrees C is missing.

> +		case hwmon_temp_min_alarm:
> +			ret = regmap_read(st->regmap,
> +					  MAX31827_CONFIGURATION_REG, &uval);
> +			uval = FIELD_GET(MAX31827_CONFIGURATION_U_TEMP_STAT_MASK,
> +					 uval);
> +			break;
> +		default:
> +			ret = -EOPNOTSUPP;

Please add
			break;
for consistency.

> +		}
> +
> +		break;
> +
> +	case hwmon_chip:
> +		if (attr == hwmon_chip_update_interval) {
> +			ret = regmap_read(st->regmap,
> +					  MAX31827_CONFIGURATION_REG, &uval);
> +			uval = FIELD_GET(MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +					 uval);
> +			switch (uval) {
> +			case MAX31827_CNV_1_DIV_64_HZ:
> +				uval = 64000;
> +				break;
> +			case MAX31827_CNV_1_DIV_32_HZ:
> +				uval = 32000;
> +				break;
> +			case MAX31827_CNV_1_DIV_16_HZ:
> +				uval = 16000;
> +				break;
> +			case MAX31827_CNV_1_DIV_4_HZ:
> +				uval = 4000;
> +				break;
> +			case MAX31827_CNV_1_HZ:
> +				uval = 1000;
> +				break;
> +			case MAX31827_CNV_4_HZ:
> +				uval = 250;
> +				break;
> +			case MAX31827_CNV_8_HZ:
> +				uval = 125;
> +				break;
> +			default:
> +				uval = 0;

				break;

> +			}
> +		}
> +		break;
> +
> +	default:
> +		ret = -EOPNOTSUPP;

Please add
		break;

here for consistency (and everywhere else where I missed it).

> +	}
> +
> +	if (ret)
> +		return ret;
> +
> +	*val = (short)uval;
> +
> +	return 0;
> +}
> +
> +static int max31827_write(struct device *dev, enum hwmon_sensor_types type,
> +			  u32 attr, int channel, long val)
> +{
> +	struct max31827_state *st = dev_get_drvdata(dev);
> +
> +	switch (type) {
> +	case hwmon_temp:
> +		switch (attr) {
> +		case hwmon_temp_enable:
> +			if (val >> 1)
> +				return -EOPNOTSUPP;
> +
> +			st->enable = val;
> +
> +			return regmap_update_bits(st->regmap,
> +						  MAX31827_CONFIGURATION_REG,
> +						  MAX31827_CONFIGURATION_1SHOT_MASK |
> +						  MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +						  MAX31827_DEVICE_ENABLE(val));
> +
> +		case hwmon_temp_max:
> +			return write_alarm_val(st, MAX31827_TH_REG, val);
> +
> +		case hwmon_temp_max_hyst:
> +			return write_alarm_val(st, MAX31827_TH_HYST_REG, val);
> +
> +		case hwmon_temp_min:
> +			return write_alarm_val(st, MAX31827_TL_REG, val);
> +
> +		case hwmon_temp_min_hyst:
> +			return write_alarm_val(st, MAX31827_TL_HYST_REG, val);
> +
> +		default:
> +			return -EOPNOTSUPP;
> +		}
> +
> +	case hwmon_chip:
> +		if (attr == hwmon_chip_update_interval) {
> +			switch (val) {
> +			case 125:
> +				val = MAX31827_CNV_8_HZ;
> +				break;
> +			case 250:
> +				val = MAX31827_CNV_4_HZ;
> +				break;
> +			case 1000:
> +				val = MAX31827_CNV_1_HZ;
> +				break;
> +			case 4000:
> +				val = MAX31827_CNV_1_DIV_4_HZ;
> +				break;
> +			case 16000:
> +				val = MAX31827_CNV_1_DIV_16_HZ;
> +				break;
> +			case 32000:
> +				val = MAX31827_CNV_1_DIV_32_HZ;
> +				break;
> +			case 64000:
> +				val = MAX31827_CNV_1_DIV_64_HZ;
> +				break;
> +			default:
> +				val = 0;
> +			}
> +
> +			if (!val)
> +				return -EOPNOTSUPP;
> +
> +			val = FIELD_PREP(MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +					 val);
> +
> +			return regmap_update_bits(st->regmap,
> +						  MAX31827_CONFIGURATION_REG,
> +						  MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +						  val);
> +		}
> +		break;
> +
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +static int max31827_init_client(struct max31827_state *st)
> +{
> +	st->enable = true;
> +
> +	return regmap_update_bits(st->regmap, MAX31827_CONFIGURATION_REG,
> +				  MAX31827_CONFIGURATION_1SHOT_MASK |
> +					  MAX31827_CONFIGURATION_CNV_RATE_MASK,
> +				  MAX31827_DEVICE_ENABLE(1));
> +}
> +
> +static const struct hwmon_channel_info *max31827_info[] = {
> +	HWMON_CHANNEL_INFO(temp, HWMON_T_ENABLE | HWMON_T_INPUT | HWMON_T_MIN |
> +					 HWMON_T_MIN_HYST | HWMON_T_MIN_ALARM |
> +					 HWMON_T_MAX | HWMON_T_MAX_HYST |
> +					 HWMON_T_MAX_ALARM),
> +	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
> +	NULL,
> +};
> +
> +static const struct hwmon_ops max31827_hwmon_ops = {
> +	.is_visible = max31827_is_visible,
> +	.read = max31827_read,
> +	.write = max31827_write,
> +};
> +
> +static const struct hwmon_chip_info max31827_chip_info = {
> +	.ops = &max31827_hwmon_ops,
> +	.info = max31827_info,
> +};
> +
> +static int max31827_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct device *hwmon_dev;
> +	struct max31827_state *st;
> +	int err;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA))
> +		return -EOPNOTSUPP;
> +
> +	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
> +	if (!st)
> +		return -ENOMEM;
> +
> +	mutex_init(&st->lock);
> +
> +	st->regmap = devm_regmap_init_i2c(client, &max31827_regmap);
> +	if (IS_ERR(st->regmap))
> +		return dev_err_probe(dev, PTR_ERR(st->regmap),
> +				     "Failed to allocate regmap.\n");
> +
> +	err = max31827_init_client(st);
> +	if (err)
> +		return err;
> +
> +	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name, st,
> +							 &max31827_chip_info,
> +							 NULL);
> +
> +	return PTR_ERR_OR_ZERO(hwmon_dev);
> +}
> +
> +static const struct i2c_device_id max31827_i2c_ids[] = {
> +	{ "max31827", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, max31827_i2c_ids);
> +

As mentioned as response to the summary patch, I don't understand why
you dropped the of table. Please explain.

> +static struct i2c_driver max31827_driver = {
> +	.class = I2C_CLASS_HWMON,
> +	.driver = {
> +		.name = "adi,max31827",

We don't usually have manufacturer prefixes in driver names, only
in devicetree compatibility tables.

> +	},
> +	.probe_new = max31827_probe,
> +	.id_table = max31827_i2c_ids,
> +};
> +module_i2c_driver(max31827_driver);
> +
> +MODULE_AUTHOR("Daniel Matyas <daniel.matyas@analog.com>");
> +MODULE_DESCRIPTION("Maxim MAX31827 low-power temperature switch driver");
> +MODULE_LICENSE("GPL");