drivers: sensors: Add driver for LM75

This commit adds a driver implementation for the LM75 I2C temperature
sensor.

Signed-off-by: Alexander Wachter <alexander.wachter@leica-geosystems.com>

drivers/sensor/CMakeLists.txt

@@ -44,6 +44,7 @@ add_subdirectory_ifdef(CONFIG_LIS2DS12		lis2ds12)
 add_subdirectory_ifdef(CONFIG_LIS2DW12          lis2dw12)
 add_subdirectory_ifdef(CONFIG_LIS2MDL		lis2mdl)
 add_subdirectory_ifdef(CONFIG_LIS3MDL		lis3mdl)
+add_subdirectory_ifdef(CONFIG_LM75  		lm75)
 add_subdirectory_ifdef(CONFIG_LPS22HB		lps22hb)
 add_subdirectory_ifdef(CONFIG_LPS22HH		lps22hh)
 add_subdirectory_ifdef(CONFIG_LPS25HB		lps25hb)

drivers/sensor/Kconfig

@@ -126,6 +126,8 @@ source "drivers/sensor/lis2mdl/Kconfig"
 
 source "drivers/sensor/lis3mdl/Kconfig"
 
+source "drivers/sensor/lm75/Kconfig"
+
 source "drivers/sensor/lps22hb/Kconfig"
 
 source "drivers/sensor/lps22hh/Kconfig"

drivers/sensor/lm75/CMakeLists.txt

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library()
+
+zephyr_library_sources(lm75.c)

drivers/sensor/lm75/Kconfig

@@ -0,0 +1,14 @@
+# LM75 temperature sensor config
+
+# Copyright (c) 2021 Leica Geosystems AG
+# SPDX-License-Identifier: Apache-2.0
+
+DT_COMPAT_LM75 := lm75
+
+config LM75
+	bool "LM75 Temperature Sensor"
+	default $(dt_compat_enabled,$(DT_COMPAT_LM75))
+	depends on I2C
+	help
+	  Enable the driver for the LM75 digital temperature Sensor with 2-wire
+	  interface. Thermal Watchdog is not implemented

drivers/sensor/lm75/lm75.c

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2021 Leica Geosystems AG
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT lm75
+
+#include <device.h>
+#include <devicetree.h>
+#include <drivers/i2c.h>
+#include <drivers/sensor.h>
+#include <logging/log.h>
+
+LOG_MODULE_REGISTER(LM75, CONFIG_SENSOR_LOG_LEVEL);
+
+
+#define LM75_REG_TEMP   0x00
+#define LM75_REG_CONFIG 0x01
+#define LM75_REG_T_HYST 0x02
+#define LM75_REG_T_OS   0x03
+
+struct lm75_data {
+	int16_t temp; /*temp in 0.1°C*/
+};
+
+struct lm75_config {
+	const struct device *i2c_dev;
+	uint8_t i2c_addr;
+};
+
+static inline int lm75_reg_read(struct lm75_config *cfg, uint8_t reg,
+				uint8_t *buf, uint32_t size)
+{
+	return i2c_burst_read(cfg->i2c_dev, cfg->i2c_addr, reg, buf, size);
+}
+
+static inline int lm75_fetch_temp(struct lm75_config *cfg, struct lm75_data *data)
+{
+	int ret;
+	uint8_t temp_read[2];
+	int16_t temp;
+
+	ret = lm75_reg_read(cfg, LM75_REG_TEMP, temp_read, sizeof(temp_read));
+	if (ret) {
+		LOG_ERR("Could not fetch temperature [%d]", ret);
+		return -EIO;
+	}
+
+	/* temp is in two's complement.
+	 *  bit 7 in the lower part corresponds to 0.5
+	 */
+	temp = temp_read[0] << 8 | temp_read[1];
+
+	/* shift right by 7, multiply by 10 to get 0.1° and divide by 2 to get °C */
+	data->temp = (temp / 128) * 10 / 2;
+
+	return 0;
+}
+
+static int lm75_sample_fetch(const struct device *dev,
+			     enum sensor_channel chan)
+{
+	struct lm75_data *data = (struct lm75_data *)dev->data;
+	struct lm75_config *cfg = (struct lm75_config *)dev->config;
+
+	switch (chan) {
+	case SENSOR_CHAN_ALL:
+	case SENSOR_CHAN_AMBIENT_TEMP:
+		return lm75_fetch_temp(cfg, data);
+	default:
+		return -ENOTSUP;
+	}
+}
+
+static int lm75_channel_get(const struct device *dev,
+			    enum sensor_channel chan,
+			    struct sensor_value *val)
+{
+	struct lm75_data *data = (struct lm75_data *)dev->data;
+
+	switch (chan) {
+	case SENSOR_CHAN_AMBIENT_TEMP:
+		val->val1 = data->temp / 10;
+		val->val2 = (data->temp - val->val1 * 10) * 100000U;
+		return 0;
+	default:
+		return -ENOTSUP;
+	}
+}
+
+static const struct sensor_driver_api lm75_driver_api = {
+	.sample_fetch = lm75_sample_fetch,
+	.channel_get = lm75_channel_get,
+};
+
+int lm75_init(const struct device *dev)
+{
+	struct lm75_config *cfg = (struct lm75_config *)dev->config;
+
+	if (device_is_ready(cfg->i2c_dev)) {
+		return 0;
+	}
+
+	LOG_ERR("I2C dev not ready");
+	return -ENODEV;
+}
+
+#define LM75_INST(inst)                                             \
+static struct lm75_data lm75_data_##inst;                           \
+static const struct lm75_config lm75_config_##inst = {              \
+	.i2c_dev = DEVICE_DT_GET(DT_INST_BUS(inst)),                \
+	.i2c_addr = DT_INST_REG_ADDR(inst),                         \
+};                                                                  \
+DEVICE_DT_INST_DEFINE(inst, lm75_init, NULL, &lm75_data_##inst,     \
+		      &lm75_config_##inst, POST_KERNEL,             \
+		      CONFIG_SENSOR_INIT_PRIORITY, &lm75_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(LM75_INST)

dts/bindings/sensor/lm75.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2021 Leica Geosystems AG
+# SPDX-License-Identifier: Apache-2.0
+
+description: LM75 Digital Temperature Sensor with 2-Wire Interface.
+
+compatible: "lm75"
+
+include: i2c-device.yaml