LinuxLists.cc - [PATCH v10 1/2] dt-bindings: hwmon: add MAX31827

2023-05-24 13:08:45

Subject: [PATCH v10 1/2] dt-bindings: hwmon: add MAX31827

2023-05-24 13:21:16

Subject: [PATCH v10 2/2] hwmon: max31827: add MAX31827 driver

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 <[email protected]>
---

v9 -> v10: Added a proper change log.

v8 -> v9: No change.

v7 -> v8: Initialised ret in max31827_read function, so that it
has a value, even if 'type == hwmon_chip && attr !=
hwmon_chip_update_interval'. (in reality it will never go there, but
needed to this this, because compiler warning)
Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/

v6 -> v7 : Used goto instead of return in write_alarm_val function.
Unlocked mutex in goto label. Used mutex for enable. Now update_interval
can only be modified if the device is enabled. I did this, b.c. modifying
the update interval, when the device is in shutdown mode, automatically
enables the device.

v5 -> v6: Corrected the mistakes with mutex. Explained why I shift the
last 4 bits in the .rst file. (because the LSB is 0.0625 degrees Celsius).

v4 -> v5: Used sign_extend32 to convert to and from milli-degrees.

v3 -> v4: Made consistency tweaks. Extended mutex_lock to every instance
of reading from or writing to st->enable. Added conversion to and from
milli-degrees. Added of_table.

v2 -> v3: Added mutex protection to reading and writing to configuration
register. Dropped of_table. Converted update_interval to Hertz.

v1 -> v2: Added max31827.rst documentation. Removed unused defines.
Removed i2c_client from private struct. Made code consistent and
cleaner. Resolved ABI abuse in hwmon_temp_enable. Added alarm attribute
support. Added write_alarm_value function to put the device in shutdown
mode before changing the alarm value and hysteresis registers. Removed
redundant error message if something went wrong with regmap_init. Used
sizeof(*st) instead of sizeof(struct max31827_state) in kzalloc.

Documentation/hwmon/index.rst | 1 +
Documentation/hwmon/max31827.rst | 90 ++++++
MAINTAINERS | 2 +
drivers/hwmon/Kconfig | 11 +
drivers/hwmon/Makefile | 2 +-
drivers/hwmon/max31827.c | 466 +++++++++++++++++++++++++++++++
6 files changed, 571 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 fa1208c62855..8cc0922f3b36 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -140,6 +140,7 @@ 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..b0971d05b8a4
--- /dev/null
+++ b/Documentation/hwmon/max31827.rst
@@ -0,0 +1,90 @@
+.. 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 <[email protected]>
+
+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.
+
+The LSB of the temperature values is 0.0625 degrees Celsius, but the values of
+the temperatures are displayed in milli-degrees. This means, that some data is
+lost. The step between 2 consecutive values is 62 or 63. This effect can be seen
+in the writing of alarm values too. For positive numbers the user-input value
+will always be rounded down to the nearest possible value, for negative numbers
+the user-input will always be rounded up to the nearest possible value.
+
+Notes
+-----
+
+Currently fault queue, alarm polarity and resolution cannot be modified.
+PEC is not implemented either.
diff --git a/MAINTAINERS b/MAINTAINERS
index 752c7e9c4e4a..53f5bd58989a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12618,6 +12618,8 @@ L: [email protected]
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: [email protected]
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index fc640201a2de..12bd17075dc4 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 cd8c568c80a9..8a8021f9ca9e 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
@@ -224,4 +225,3 @@ 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..fa86e5a72935
--- /dev/null
+++ b/drivers/hwmon/max31827.c
@@ -0,0 +1,466 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * max31827.c - Support for Maxim Low-Power Switch
+ *
+ * Copyright (c) 2023 Daniel Matyas <[email protected]>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bitops.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_16_BIT_TO_M_DGR(x) (sign_extend32(x, 15) * 1000 / 16)
+#define MAX31827_M_DGR_TO_16_BIT(x) (((x) << 4) / 1000)
+#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;
+
+ val = MAX31827_M_DGR_TO_16_BIT(val);
+
+ /*
+ * 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.
+ */
+ mutex_lock(&st->lock);
+
+ if (!st->enable) {
+ ret = regmap_write(st->regmap, reg, val);
+ goto unlock;
+ }
+
+ ret = regmap_read(st->regmap, MAX31827_CONFIGURATION_REG, &cfg);
+ if (ret)
+ goto unlock;
+
+ tmp = cfg & ~(MAX31827_CONFIGURATION_1SHOT_MASK |
+ MAX31827_CONFIGURATION_CNV_RATE_MASK);
+ ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, tmp);
+ if (ret)
+ goto unlock;
+
+ ret = regmap_write(st->regmap, reg, val);
+ if (ret)
+ goto unlock;
+
+ ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, cfg);
+
+unlock:
+ 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;
+ default:
+ return 0;
+ }
+ } 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 = 0;
+
+ switch (type) {
+ case hwmon_temp:
+ switch (attr) {
+ case hwmon_temp_enable:
+ ret = regmap_read(st->regmap,
+ MAX31827_CONFIGURATION_REG, &uval);
+ if (ret)
+ break;
+
+ uval = FIELD_GET(MAX31827_CONFIGURATION_1SHOT_MASK |
+ MAX31827_CONFIGURATION_CNV_RATE_MASK,
+ uval);
+ *val = !!uval;
+
+ break;
+ case hwmon_temp_input:
+ mutex_lock(&st->lock);
+
+ if (!st->enable) {
+ /*
+ * This operation requires mutex protection,
+ * because the chip configuration should not
+ * be changed during the conversion process.
+ */
+
+ ret = regmap_update_bits(st->regmap,
+ MAX31827_CONFIGURATION_REG,
+ MAX31827_CONFIGURATION_1SHOT_MASK,
+ 1);
+ if (ret) {
+ mutex_unlock(&st->lock);
+ return ret;
+ }
+
+ msleep(MAX31827_12_BIT_CNV_TIME);
+ }
+ ret = regmap_read(st->regmap, MAX31827_T_REG, &uval);
+
+ mutex_unlock(&st->lock);
+
+ if (ret)
+ break;
+
+ *val = MAX31827_16_BIT_TO_M_DGR(uval);
+
+ break;
+ case hwmon_temp_max:
+ ret = regmap_read(st->regmap, MAX31827_TH_REG, &uval);
+ if (ret)
+ break;
+
+ *val = MAX31827_16_BIT_TO_M_DGR(uval);
+ break;
+ case hwmon_temp_max_hyst:
+ ret = regmap_read(st->regmap, MAX31827_TH_HYST_REG,
+ &uval);
+ if (ret)
+ break;
+
+ *val = MAX31827_16_BIT_TO_M_DGR(uval);
+ break;
+ case hwmon_temp_max_alarm:
+ ret = regmap_read(st->regmap,
+ MAX31827_CONFIGURATION_REG, &uval);
+ if (ret)
+ break;
+
+ *val = FIELD_GET(MAX31827_CONFIGURATION_O_TEMP_STAT_MASK,
+ uval);
+ break;
+ case hwmon_temp_min:
+ ret = regmap_read(st->regmap, MAX31827_TL_REG, &uval);
+ if (ret)
+ break;
+
+ *val = MAX31827_16_BIT_TO_M_DGR(uval);
+ break;
+ case hwmon_temp_min_hyst:
+ ret = regmap_read(st->regmap, MAX31827_TL_HYST_REG,
+ &uval);
+ if (ret)
+ break;
+
+ *val = MAX31827_16_BIT_TO_M_DGR(uval);
+ break;
+ case hwmon_temp_min_alarm:
+ ret = regmap_read(st->regmap,
+ MAX31827_CONFIGURATION_REG, &uval);
+ if (ret)
+ break;
+
+ *val = FIELD_GET(MAX31827_CONFIGURATION_U_TEMP_STAT_MASK,
+ uval);
+ break;
+ default:
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
+ break;
+
+ case hwmon_chip:
+ if (attr == hwmon_chip_update_interval) {
+ ret = regmap_read(st->regmap,
+ MAX31827_CONFIGURATION_REG, &uval);
+ if (ret)
+ break;
+
+ uval = FIELD_GET(MAX31827_CONFIGURATION_CNV_RATE_MASK,
+ uval);
+ switch (uval) {
+ case MAX31827_CNV_1_DIV_64_HZ:
+ *val = 64000;
+ break;
+ case MAX31827_CNV_1_DIV_32_HZ:
+ *val = 32000;
+ break;
+ case MAX31827_CNV_1_DIV_16_HZ:
+ *val = 16000;
+ break;
+ case MAX31827_CNV_1_DIV_4_HZ:
+ *val = 4000;
+ break;
+ case MAX31827_CNV_1_HZ:
+ *val = 1000;
+ break;
+ case MAX31827_CNV_4_HZ:
+ *val = 250;
+ break;
+ case MAX31827_CNV_8_HZ:
+ *val = 125;
+ break;
+ default:
+ *val = 0;
+ break;
+ }
+ }
+ break;
+
+ default:
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
+ return ret;
+}
+
+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);
+ int ret;
+
+ switch (type) {
+ case hwmon_temp:
+ switch (attr) {
+ case hwmon_temp_enable:
+ if (val >> 1)
+ return -EOPNOTSUPP;
+
+ mutex_lock(&st->lock);
+ /**
+ * The chip should not be enabled while a conversion is
+ * performed. Neither should the chip be enabled when
+ * the alarm values are changed.
+ */
+
+ st->enable = val;
+
+ ret = regmap_update_bits(st->regmap,
+ MAX31827_CONFIGURATION_REG,
+ MAX31827_CONFIGURATION_1SHOT_MASK |
+ MAX31827_CONFIGURATION_CNV_RATE_MASK,
+ MAX31827_DEVICE_ENABLE(val));
+
+ mutex_unlock(&st->lock);
+
+ return ret;
+
+ 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) {
+ if (!st->enable)
+ return -EOPNOTSUPP;
+
+ 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:
+ 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);
+
+static const struct of_device_id max31827_of_match[] = {
+ { .compatible = "max31827" },
+ { }
+};
+MODULE_DEVICE_TABLE(of, max31827_of_match);
+
+static struct i2c_driver max31827_driver = {
+ .class = I2C_CLASS_HWMON,
+ .driver = {
+ .name = "max31827",
+ .of_match_table = max31827_of_match,
+ },
+ .probe_new = max31827_probe,
+ .id_table = max31827_i2c_ids,
+};
+module_i2c_driver(max31827_driver);
+
+MODULE_AUTHOR("Daniel Matyas <[email protected]>");
+MODULE_DESCRIPTION("Maxim MAX31827 low-power temperature switch driver");
+MODULE_LICENSE("GPL");
--
2.34.1

2023-06-07 17:56:11

by Rob Herring (Arm)

[permalink] [raw]

Subject: Re: [PATCH v10 2/2] hwmon: max31827: add MAX31827 driver

On Wed, May 24, 2023 at 07:01:30PM +0300, 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 <[email protected]>
> ---
>
> v9 -> v10: Added a proper change log.
>
> v8 -> v9: No change.
>
> v7 -> v8: Initialised ret in max31827_read function, so that it
> has a value, even if 'type == hwmon_chip && attr !=
> hwmon_chip_update_interval'. (in reality it will never go there, but
> needed to this this, because compiler warning)
> Reported-by: kernel test robot <[email protected]>
> Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/
>
> v6 -> v7 : Used goto instead of return in write_alarm_val function.
> Unlocked mutex in goto label. Used mutex for enable. Now update_interval
> can only be modified if the device is enabled. I did this, b.c. modifying
> the update interval, when the device is in shutdown mode, automatically
> enables the device.
>
> v5 -> v6: Corrected the mistakes with mutex. Explained why I shift the
> last 4 bits in the .rst file. (because the LSB is 0.0625 degrees Celsius).
>
> v4 -> v5: Used sign_extend32 to convert to and from milli-degrees.
>
> v3 -> v4: Made consistency tweaks. Extended mutex_lock to every instance
> of reading from or writing to st->enable. Added conversion to and from
> milli-degrees. Added of_table.
>
> v2 -> v3: Added mutex protection to reading and writing to configuration
> register. Dropped of_table. Converted update_interval to Hertz.
>
> v1 -> v2: Added max31827.rst documentation. Removed unused defines.
> Removed i2c_client from private struct. Made code consistent and
> cleaner. Resolved ABI abuse in hwmon_temp_enable. Added alarm attribute
> support. Added write_alarm_value function to put the device in shutdown
> mode before changing the alarm value and hysteresis registers. Removed
> redundant error message if something went wrong with regmap_init. Used
> sizeof(*st) instead of sizeof(struct max31827_state) in kzalloc.
>
> Documentation/hwmon/index.rst | 1 +
> Documentation/hwmon/max31827.rst | 90 ++++++
> MAINTAINERS | 2 +
> drivers/hwmon/Kconfig | 11 +
> drivers/hwmon/Makefile | 2 +-
> drivers/hwmon/max31827.c | 466 +++++++++++++++++++++++++++++++
> 6 files changed, 571 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 fa1208c62855..8cc0922f3b36 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -140,6 +140,7 @@ 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..b0971d05b8a4
> --- /dev/null
> +++ b/Documentation/hwmon/max31827.rst
> @@ -0,0 +1,90 @@
> +.. 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 <[email protected]>
> +
> +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.
> +
> +The LSB of the temperature values is 0.0625 degrees Celsius, but the values of
> +the temperatures are displayed in milli-degrees. This means, that some data is
> +lost. The step between 2 consecutive values is 62 or 63. This effect can be seen
> +in the writing of alarm values too. For positive numbers the user-input value
> +will always be rounded down to the nearest possible value, for negative numbers
> +the user-input will always be rounded up to the nearest possible value.
> +
> +Notes
> +-----
> +
> +Currently fault queue, alarm polarity and resolution cannot be modified.
> +PEC is not implemented either.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 752c7e9c4e4a..53f5bd58989a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -12618,6 +12618,8 @@ L: [email protected]
> 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: [email protected]
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index fc640201a2de..12bd17075dc4 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 cd8c568c80a9..8a8021f9ca9e 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
> @@ -224,4 +225,3 @@ 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..fa86e5a72935
> --- /dev/null
> +++ b/drivers/hwmon/max31827.c
> @@ -0,0 +1,466 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * max31827.c - Support for Maxim Low-Power Switch
> + *
> + * Copyright (c) 2023 Daniel Matyas <[email protected]>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.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_16_BIT_TO_M_DGR(x) (sign_extend32(x, 15) * 1000 / 16)
> +#define MAX31827_M_DGR_TO_16_BIT(x) (((x) << 4) / 1000)
> +#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;
> +
> + val = MAX31827_M_DGR_TO_16_BIT(val);
> +
> + /*
> + * 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.
> + */
> + mutex_lock(&st->lock);
> +
> + if (!st->enable) {
> + ret = regmap_write(st->regmap, reg, val);
> + goto unlock;
> + }
> +
> + ret = regmap_read(st->regmap, MAX31827_CONFIGURATION_REG, &cfg);
> + if (ret)
> + goto unlock;
> +
> + tmp = cfg & ~(MAX31827_CONFIGURATION_1SHOT_MASK |
> + MAX31827_CONFIGURATION_CNV_RATE_MASK);
> + ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, tmp);
> + if (ret)
> + goto unlock;
> +
> + ret = regmap_write(st->regmap, reg, val);
> + if (ret)
> + goto unlock;
> +
> + ret = regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, cfg);
> +
> +unlock:
> + 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;
> + default:
> + return 0;
> + }
> + } 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 = 0;
> +
> + switch (type) {
> + case hwmon_temp:
> + switch (attr) {
> + case hwmon_temp_enable:
> + ret = regmap_read(st->regmap,
> + MAX31827_CONFIGURATION_REG, &uval);
> + if (ret)
> + break;
> +
> + uval = FIELD_GET(MAX31827_CONFIGURATION_1SHOT_MASK |
> + MAX31827_CONFIGURATION_CNV_RATE_MASK,
> + uval);
> + *val = !!uval;
> +
> + break;
> + case hwmon_temp_input:
> + mutex_lock(&st->lock);
> +
> + if (!st->enable) {
> + /*
> + * This operation requires mutex protection,
> + * because the chip configuration should not
> + * be changed during the conversion process.
> + */
> +
> + ret = regmap_update_bits(st->regmap,
> + MAX31827_CONFIGURATION_REG,
> + MAX31827_CONFIGURATION_1SHOT_MASK,
> + 1);
> + if (ret) {
> + mutex_unlock(&st->lock);
> + return ret;
> + }
> +
> + msleep(MAX31827_12_BIT_CNV_TIME);
> + }
> + ret = regmap_read(st->regmap, MAX31827_T_REG, &uval);
> +
> + mutex_unlock(&st->lock);
> +
> + if (ret)
> + break;
> +
> + *val = MAX31827_16_BIT_TO_M_DGR(uval);
> +
> + break;
> + case hwmon_temp_max:
> + ret = regmap_read(st->regmap, MAX31827_TH_REG, &uval);
> + if (ret)
> + break;
> +
> + *val = MAX31827_16_BIT_TO_M_DGR(uval);
> + break;
> + case hwmon_temp_max_hyst:
> + ret = regmap_read(st->regmap, MAX31827_TH_HYST_REG,
> + &uval);
> + if (ret)
> + break;
> +
> + *val = MAX31827_16_BIT_TO_M_DGR(uval);
> + break;
> + case hwmon_temp_max_alarm:
> + ret = regmap_read(st->regmap,
> + MAX31827_CONFIGURATION_REG, &uval);
> + if (ret)
> + break;
> +
> + *val = FIELD_GET(MAX31827_CONFIGURATION_O_TEMP_STAT_MASK,
> + uval);
> + break;
> + case hwmon_temp_min:
> + ret = regmap_read(st->regmap, MAX31827_TL_REG, &uval);
> + if (ret)
> + break;
> +
> + *val = MAX31827_16_BIT_TO_M_DGR(uval);
> + break;
> + case hwmon_temp_min_hyst:
> + ret = regmap_read(st->regmap, MAX31827_TL_HYST_REG,
> + &uval);
> + if (ret)
> + break;
> +
> + *val = MAX31827_16_BIT_TO_M_DGR(uval);
> + break;
> + case hwmon_temp_min_alarm:
> + ret = regmap_read(st->regmap,
> + MAX31827_CONFIGURATION_REG, &uval);
> + if (ret)
> + break;
> +
> + *val = FIELD_GET(MAX31827_CONFIGURATION_U_TEMP_STAT_MASK,
> + uval);
> + break;
> + default:
> + ret = -EOPNOTSUPP;
> + break;
> + }
> +
> + break;
> +
> + case hwmon_chip:
> + if (attr == hwmon_chip_update_interval) {
> + ret = regmap_read(st->regmap,
> + MAX31827_CONFIGURATION_REG, &uval);
> + if (ret)
> + break;
> +
> + uval = FIELD_GET(MAX31827_CONFIGURATION_CNV_RATE_MASK,
> + uval);
> + switch (uval) {
> + case MAX31827_CNV_1_DIV_64_HZ:
> + *val = 64000;
> + break;
> + case MAX31827_CNV_1_DIV_32_HZ:
> + *val = 32000;
> + break;
> + case MAX31827_CNV_1_DIV_16_HZ:
> + *val = 16000;
> + break;
> + case MAX31827_CNV_1_DIV_4_HZ:
> + *val = 4000;
> + break;
> + case MAX31827_CNV_1_HZ:
> + *val = 1000;
> + break;
> + case MAX31827_CNV_4_HZ:
> + *val = 250;
> + break;
> + case MAX31827_CNV_8_HZ:
> + *val = 125;
> + break;
> + default:
> + *val = 0;
> + break;
> + }
> + }
> + break;
> +
> + default:
> + ret = -EOPNOTSUPP;
> + break;
> + }
> +
> + return ret;
> +}
> +
> +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);
> + int ret;
> +
> + switch (type) {
> + case hwmon_temp:
> + switch (attr) {
> + case hwmon_temp_enable:
> + if (val >> 1)
> + return -EOPNOTSUPP;
> +
> + mutex_lock(&st->lock);
> + /**
> + * The chip should not be enabled while a conversion is
> + * performed. Neither should the chip be enabled when
> + * the alarm values are changed.
> + */
> +
> + st->enable = val;
> +
> + ret = regmap_update_bits(st->regmap,
> + MAX31827_CONFIGURATION_REG,
> + MAX31827_CONFIGURATION_1SHOT_MASK |
> + MAX31827_CONFIGURATION_CNV_RATE_MASK,
> + MAX31827_DEVICE_ENABLE(val));
> +
> + mutex_unlock(&st->lock);
> +
> + return ret;
> +
> + 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) {
> + if (!st->enable)
> + return -EOPNOTSUPP;
> +
> + 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:
> + 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);
> +
> +static const struct of_device_id max31827_of_match[] = {
> + { .compatible = "max31827" },

Doesn't match what the binding says (binding is correct).

Reported by 'make dt_compatible_check'.

Rob