hwmon: (max31722) Add support for MAX31722/MAX31723 temperature sensors

Add basic support for the Maxim Integrated MAX31722/MAX31723 SPI
temperature sensors / thermostats.

Includes:
    - ACPI support;
    - raw temperature readings;
    - power management

Datasheet:
https://datasheets.maximintegrated.com/en/ds/MAX31722-MAX31723.pdf

Signed-off-by: Tiberiu Breana <tiberiu.a.breana@intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

4 files changed, 210 insertions, 0 deletions

diff --git a/Documentation/hwmon/max31722 b/Documentation/hwmon/max31722
new file mode 100644
index 000000000000..090da84538c8
--- /dev/null
+++ b/Documentation/hwmon/max31722
@@ -0,0 +1,34 @@
+Kernel driver max31722
+======================
+
+Supported chips:
+  * Maxim Integrated MAX31722
+    Prefix: 'max31722'
+    ACPI ID: MAX31722
+    Addresses scanned: -
+    Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX31722-MAX31723.pdf
+  * Maxim Integrated MAX31723
+    Prefix: 'max31723'
+    ACPI ID: MAX31723
+    Addresses scanned: -
+    Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX31722-MAX31723.pdf
+
+Author: Tiberiu Breana <tiberiu.a.breana@intel.com>
+
+Description
+-----------
+
+This driver adds support for the Maxim Integrated MAX31722/MAX31723 thermometers
+and thermostats running over an SPI interface.
+
+Usage Notes
+-----------
+
+This driver uses ACPI to auto-detect devices. See ACPI IDs in the above section.
+
+Sysfs entries
+-------------
+
+The following attribute is supported:
+
+temp1_input             Measured temperature. Read-only.
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 5c2d13a687aa..bdfa39408996 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -821,6 +821,16 @@ config SENSORS_MAX197
           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
+        help
+          Support for the Maxim Integrated MAX31722/MAX31723 digital
+          thermometers/thermostats operating over an SPI interface.
+
+          This driver can also be built as a module. If so, the module
+          will be called max31722.
+
 config SENSORS_MAX6639
         tristate "Maxim MAX6639 sensor chip"
         depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 58cc3acba7e7..2ef5b7c4c54f 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -112,6 +112,7 @@ 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_MAX6639)   += max6639.o
 obj-$(CONFIG_SENSORS_MAX6642)   += max6642.o
 obj-$(CONFIG_SENSORS_MAX6650)   += max6650.o
diff --git a/drivers/hwmon/max31722.c b/drivers/hwmon/max31722.c
new file mode 100644
index 000000000000..30a100e70a0d
--- /dev/null
+++ b/drivers/hwmon/max31722.c
@@ -0,0 +1,165 @@
+/*
+ * max31722 - hwmon driver for Maxim Integrated MAX31722/MAX31723 SPI
+ * digital thermometer and thermostats.
+ *
+ * Copyright (c) 2016, Intel Corporation.
+ *
+ * This file is subject to the terms and conditions of version 2 of
+ * the GNU General Public License. See the file COPYING in the main
+ * directory of this archive for more details.
+ */
+
+#include <linux/acpi.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+
+#define MAX31722_REG_CFG                                0x00
+#define MAX31722_REG_TEMP_LSB                           0x01
+
+#define MAX31722_MODE_CONTINUOUS                        0x00
+#define MAX31722_MODE_STANDBY                           0x01
+#define MAX31722_MODE_MASK                              0xFE
+#define MAX31722_RESOLUTION_12BIT                       0x06
+#define MAX31722_WRITE_MASK                             0x80
+
+struct max31722_data {
+        struct device *hwmon_dev;
+        struct spi_device *spi_device;
+        u8 mode;
+};
+
+static int max31722_set_mode(struct max31722_data *data, u8 mode)
+{
+        int ret;
+        struct spi_device *spi = data->spi_device;
+        u8 buf[2] = {
+                MAX31722_REG_CFG | MAX31722_WRITE_MASK,
+                (data->mode & MAX31722_MODE_MASK) | mode
+        };
+
+        ret = spi_write(spi, &buf, sizeof(buf));
+        if (ret < 0) {
+                dev_err(&spi->dev, "failed to set sensor mode.\n");
+                return ret;
+        }
+        data->mode = (data->mode & MAX31722_MODE_MASK) | mode;
+
+        return 0;
+}
+
+static ssize_t max31722_show_temp(struct device *dev,
+                                  struct device_attribute *attr,
+                                  char *buf)
+{
+        ssize_t ret;
+        struct max31722_data *data = dev_get_drvdata(dev);
+
+        ret = spi_w8r16(data->spi_device, MAX31722_REG_TEMP_LSB);
+        if (ret < 0)
+                return ret;
+        /* Keep 12 bits and multiply by the scale of 62.5 millidegrees/bit. */
+        return sprintf(buf, "%d\n", (s16)le16_to_cpu(ret) * 125 / 32);
+}
+
+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
+                          max31722_show_temp, NULL, 0);
+
+static struct attribute *max31722_attrs[] = {
+        &sensor_dev_attr_temp1_input.dev_attr.attr,
+        NULL,
+};
+
+ATTRIBUTE_GROUPS(max31722);
+
+static int max31722_probe(struct spi_device *spi)
+{
+        int ret;
+        struct max31722_data *data;
+
+        data = devm_kzalloc(&spi->dev, sizeof(*data), GFP_KERNEL);
+        if (!data)
+                return -ENOMEM;
+
+        spi_set_drvdata(spi, data);
+        data->spi_device = spi;
+        /*
+         * Set SD bit to 0 so we can have continuous measurements.
+         * Set resolution to 12 bits for maximum precision.
+         */
+        data->mode = MAX31722_MODE_CONTINUOUS | MAX31722_RESOLUTION_12BIT;
+        ret = max31722_set_mode(data, MAX31722_MODE_CONTINUOUS);
+        if (ret < 0)
+                return ret;
+
+        data->hwmon_dev = hwmon_device_register_with_groups(&spi->dev,
+                                                            spi->modalias,
+                                                            data,
+                                                            max31722_groups);
+        if (IS_ERR(data->hwmon_dev)) {
+                max31722_set_mode(data, MAX31722_MODE_STANDBY);
+                return PTR_ERR(data->hwmon_dev);
+        }
+
+        return 0;
+}
+
+static int max31722_remove(struct spi_device *spi)
+{
+        struct max31722_data *data = spi_get_drvdata(spi);
+
+        hwmon_device_unregister(data->hwmon_dev);
+
+        return max31722_set_mode(data, MAX31722_MODE_STANDBY);
+}
+
+static int __maybe_unused max31722_suspend(struct device *dev)
+{
+        struct spi_device *spi_device = to_spi_device(dev);
+        struct max31722_data *data = spi_get_drvdata(spi_device);
+
+        return max31722_set_mode(data, MAX31722_MODE_STANDBY);
+}
+
+static int __maybe_unused max31722_resume(struct device *dev)
+{
+        struct spi_device *spi_device = to_spi_device(dev);
+        struct max31722_data *data = spi_get_drvdata(spi_device);
+
+        return max31722_set_mode(data, MAX31722_MODE_CONTINUOUS);
+}
+
+static SIMPLE_DEV_PM_OPS(max31722_pm_ops, max31722_suspend, max31722_resume);
+
+static const struct spi_device_id max31722_spi_id[] = {
+        {"max31722", 0},
+        {"max31723", 0},
+        {}
+};
+
+static const struct acpi_device_id __maybe_unused max31722_acpi_id[] = {
+        {"MAX31722", 0},
+        {"MAX31723", 0},
+        {}
+};
+
+MODULE_DEVICE_TABLE(spi, max31722_spi_id);
+
+static struct spi_driver max31722_driver = {
+        .driver = {
+                .name = "max31722",
+                .pm = &max31722_pm_ops,
+                .acpi_match_table = ACPI_PTR(max31722_acpi_id),
+        },
+        .probe =            max31722_probe,
+        .remove =           max31722_remove,
+        .id_table =         max31722_spi_id,
+};
+
+module_spi_driver(max31722_driver);
+
+MODULE_AUTHOR("Tiberiu Breana <tiberiu.a.breana@intel.com>");
+MODULE_DESCRIPTION("max31722 sensor driver");
+MODULE_LICENSE("GPL v2");