hwmon: add ChromeOS EC driver

The ChromeOS Embedded Controller exposes fan speed and temperature
readings.
Expose this data through the hwmon subsystem.

The driver is designed to be probed via the cros_ec mfd device.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240529-cros_ec-hwmon-v4-2-5cdf0c5db50a@weissschuh.net
[tzungbi: Fixed typo in MAINTAINERS: "chros_ec_hwmon" -> "cros_ec_hwmon"]
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

Documentation/hwmon/cros_ec_hwmon.rst

@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver cros_ec_hwmon
+===========================
+
+Supported chips:
+
+  * ChromeOS embedded controllers.
+
+    Prefix: 'cros_ec'
+
+    Addresses scanned: -
+
+Author:
+
+  - Thomas Weißschuh <linux@weissschuh.net>
+
+Description
+-----------
+
+This driver implements support for hardware monitoring commands exposed by the
+ChromeOS embedded controller used in Chromebooks and other devices.
+
+The channel labels exposed via hwmon are retrieved from the EC itself.
+
+Fan and temperature readings are supported.

Documentation/hwmon/index.rst

@@ -58,6 +58,7 @@ Hardware Monitoring Kernel Drivers
    coretemp
    corsair-cpro
    corsair-psu
+   cros_ec_hwmon
    da9052
    da9055
    dell-smm-hwmon

MAINTAINERS

@@ -5135,6 +5135,14 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/sound/google,cros-ec-codec.yaml
 F:	sound/soc/codecs/cros_ec_codec.*
 
+CHROMEOS EC HARDWARE MONITORING
+M:	Thomas Weißschuh <thomas@weissschuh.net>
+L:	chrome-platform@lists.linux.dev
+L:	linux-hwmon@vger.kernel.org
+S:	Maintained
+F:	Documentation/hwmon/cros_ec_hwmon.rst
+F:	drivers/hwmon/cros_ec_hwmon.c
+
 CHROMEOS EC SUBDRIVERS
 M:	Benson Leung <bleung@chromium.org>
 R:	Guenter Roeck <groeck@chromium.org>

drivers/hwmon/Kconfig

@@ -506,6 +506,17 @@ config SENSORS_CORSAIR_PSU
 	  This driver can also be built as a module. If so, the module
 	  will be called corsair-psu.
 
+config SENSORS_CROS_EC
+	tristate "ChromeOS Embedded Controller sensors"
+	depends on MFD_CROS_EC_DEV
+	default MFD_CROS_EC_DEV
+	help
+	  If you say yes here you get support for ChromeOS Embedded Controller
+	  sensors.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called cros_ec_hwmon.
+
 config SENSORS_DRIVETEMP
 	tristate "Hard disk drives with temperature sensors"
 	depends on SCSI && ATA

drivers/hwmon/Makefile

@@ -64,6 +64,7 @@ obj-$(CONFIG_SENSORS_CHIPCAP2) += chipcap2.o
 obj-$(CONFIG_SENSORS_CORETEMP)	+= coretemp.o
 obj-$(CONFIG_SENSORS_CORSAIR_CPRO) += corsair-cpro.o
 obj-$(CONFIG_SENSORS_CORSAIR_PSU) += corsair-psu.o
+obj-$(CONFIG_SENSORS_CROS_EC)	+= cros_ec_hwmon.o
 obj-$(CONFIG_SENSORS_DA9052_ADC)+= da9052-hwmon.o
 obj-$(CONFIG_SENSORS_DA9055)+= da9055-hwmon.o
 obj-$(CONFIG_SENSORS_DELL_SMM)	+= dell-smm-hwmon.o

drivers/hwmon/cros_ec_hwmon.c

@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  ChromeOS EC driver for hwmon
+ *
+ *  Copyright (C) 2024 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+#include <linux/device.h>
+#include <linux/hwmon.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/platform_data/cros_ec_commands.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#define DRV_NAME	"cros-ec-hwmon"
+
+struct cros_ec_hwmon_priv {
+	struct cros_ec_device *cros_ec;
+	const char *temp_sensor_names[EC_TEMP_SENSOR_ENTRIES + EC_TEMP_SENSOR_B_ENTRIES];
+	u8 usable_fans;
+};
+
+static int cros_ec_hwmon_read_fan_speed(struct cros_ec_device *cros_ec, u8 index, u16 *speed)
+{
+	int ret;
+
+	ret = cros_ec_cmd_readmem(cros_ec, EC_MEMMAP_FAN + index * 2, 2, speed);
+	if (ret < 0)
+		return ret;
+
+	*speed = le16_to_cpu(*speed);
+	return 0;
+}
+
+static int cros_ec_hwmon_read_temp(struct cros_ec_device *cros_ec, u8 index, u8 *temp)
+{
+	unsigned int offset;
+	int ret;
+
+	if (index < EC_TEMP_SENSOR_ENTRIES)
+		offset = EC_MEMMAP_TEMP_SENSOR + index;
+	else
+		offset = EC_MEMMAP_TEMP_SENSOR_B + index - EC_TEMP_SENSOR_ENTRIES;
+
+	ret = cros_ec_cmd_readmem(cros_ec, offset, 1, temp);
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
+static bool cros_ec_hwmon_is_error_fan(u16 speed)
+{
+	return speed == EC_FAN_SPEED_NOT_PRESENT || speed == EC_FAN_SPEED_STALLED;
+}
+
+static bool cros_ec_hwmon_is_error_temp(u8 temp)
+{
+	return temp == EC_TEMP_SENSOR_NOT_PRESENT     ||
+	       temp == EC_TEMP_SENSOR_ERROR           ||
+	       temp == EC_TEMP_SENSOR_NOT_POWERED     ||
+	       temp == EC_TEMP_SENSOR_NOT_CALIBRATED;
+}
+
+static long cros_ec_hwmon_temp_to_millicelsius(u8 temp)
+{
+	return kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET));
+}
+
+static int cros_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
+			      u32 attr, int channel, long *val)
+{
+	struct cros_ec_hwmon_priv *priv = dev_get_drvdata(dev);
+	int ret = -EOPNOTSUPP;
+	u16 speed;
+	u8 temp;
+
+	if (type == hwmon_fan) {
+		if (attr == hwmon_fan_input) {
+			ret = cros_ec_hwmon_read_fan_speed(priv->cros_ec, channel, &speed);
+			if (ret == 0) {
+				if (cros_ec_hwmon_is_error_fan(speed))
+					ret = -ENODATA;
+				else
+					*val = speed;
+			}
+		} else if (attr == hwmon_fan_fault) {
+			ret = cros_ec_hwmon_read_fan_speed(priv->cros_ec, channel, &speed);
+			if (ret == 0)
+				*val = cros_ec_hwmon_is_error_fan(speed);
+		}
+	} else if (type == hwmon_temp) {
+		if (attr == hwmon_temp_input) {
+			ret = cros_ec_hwmon_read_temp(priv->cros_ec, channel, &temp);
+			if (ret == 0) {
+				if (cros_ec_hwmon_is_error_temp(temp))
+					ret = -ENODATA;
+				else
+					*val = cros_ec_hwmon_temp_to_millicelsius(temp);
+			}
+		} else if (attr == hwmon_temp_fault) {
+			ret = cros_ec_hwmon_read_temp(priv->cros_ec, channel, &temp);
+			if (ret == 0)
+				*val = cros_ec_hwmon_is_error_temp(temp);
+		}
+	}
+
+	return ret;
+}
+
+static int cros_ec_hwmon_read_string(struct device *dev, enum hwmon_sensor_types type,
+				     u32 attr, int channel, const char **str)
+{
+	struct cros_ec_hwmon_priv *priv = dev_get_drvdata(dev);
+
+	if (type == hwmon_temp && attr == hwmon_temp_label) {
+		*str = priv->temp_sensor_names[channel];
+		return 0;
+	}
+
+	return -EOPNOTSUPP;
+}
+
+static umode_t cros_ec_hwmon_is_visible(const void *data, enum hwmon_sensor_types type,
+					u32 attr, int channel)
+{
+	const struct cros_ec_hwmon_priv *priv = data;
+
+	if (type == hwmon_fan) {
+		if (priv->usable_fans & BIT(channel))
+			return 0444;
+	} else if (type == hwmon_temp) {
+		if (priv->temp_sensor_names[channel])
+			return 0444;
+	}
+
+	return 0;
+}
+
+static const struct hwmon_channel_info * const cros_ec_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(fan,
+			   HWMON_F_INPUT | HWMON_F_FAULT,
+			   HWMON_F_INPUT | HWMON_F_FAULT,
+			   HWMON_F_INPUT | HWMON_F_FAULT,
+			   HWMON_F_INPUT | HWMON_F_FAULT),
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_FAULT | HWMON_T_LABEL),
+	NULL
+};
+
+static const struct hwmon_ops cros_ec_hwmon_ops = {
+	.read = cros_ec_hwmon_read,
+	.read_string = cros_ec_hwmon_read_string,
+	.is_visible = cros_ec_hwmon_is_visible,
+};
+
+static const struct hwmon_chip_info cros_ec_hwmon_chip_info = {
+	.ops = &cros_ec_hwmon_ops,
+	.info = cros_ec_hwmon_info,
+};
+
+static void cros_ec_hwmon_probe_temp_sensors(struct device *dev, struct cros_ec_hwmon_priv *priv,
+					     u8 thermal_version)
+{
+	struct ec_params_temp_sensor_get_info req = {};
+	struct ec_response_temp_sensor_get_info resp;
+	size_t candidates, i, sensor_name_size;
+	int ret;
+	u8 temp;
+
+	if (thermal_version < 2)
+		candidates = EC_TEMP_SENSOR_ENTRIES;
+	else
+		candidates = ARRAY_SIZE(priv->temp_sensor_names);
+
+	for (i = 0; i < candidates; i++) {
+		if (cros_ec_hwmon_read_temp(priv->cros_ec, i, &temp) < 0)
+			continue;
+
+		if (temp == EC_TEMP_SENSOR_NOT_PRESENT)
+			continue;
+
+		req.id = i;
+		ret = cros_ec_cmd(priv->cros_ec, 0, EC_CMD_TEMP_SENSOR_GET_INFO,
+				  &req, sizeof(req), &resp, sizeof(resp));
+		if (ret < 0)
+			continue;
+
+		sensor_name_size = strnlen(resp.sensor_name, sizeof(resp.sensor_name));
+		priv->temp_sensor_names[i] = devm_kasprintf(dev, GFP_KERNEL, "%*s",
+							    (int)sensor_name_size,
+							    resp.sensor_name);
+	}
+}
+
+static void cros_ec_hwmon_probe_fans(struct cros_ec_hwmon_priv *priv)
+{
+	u16 speed;
+	size_t i;
+	int ret;
+
+	for (i = 0; i < EC_FAN_SPEED_ENTRIES; i++) {
+		ret = cros_ec_hwmon_read_fan_speed(priv->cros_ec, i, &speed);
+		if (ret == 0 && speed != EC_FAN_SPEED_NOT_PRESENT)
+			priv->usable_fans |= BIT(i);
+	}
+}
+
+static int cros_ec_hwmon_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct cros_ec_dev *ec_dev = dev_get_drvdata(dev->parent);
+	struct cros_ec_device *cros_ec = ec_dev->ec_dev;
+	struct cros_ec_hwmon_priv *priv;
+	struct device *hwmon_dev;
+	u8 thermal_version;
+	int ret;
+
+	ret = cros_ec_cmd_readmem(cros_ec, EC_MEMMAP_THERMAL_VERSION, 1, &thermal_version);
+	if (ret < 0)
+		return ret;
+
+	/* Covers both fan and temp sensors */
+	if (thermal_version == 0)
+		return -ENODEV;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->cros_ec = cros_ec;
+
+	cros_ec_hwmon_probe_temp_sensors(dev, priv, thermal_version);
+	cros_ec_hwmon_probe_fans(priv);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, "cros_ec", priv,
+							 &cros_ec_hwmon_chip_info, NULL);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct platform_device_id cros_ec_hwmon_id[] = {
+	{ DRV_NAME, 0 },
+	{}
+};
+
+static struct platform_driver cros_ec_hwmon_driver = {
+	.driver.name	= DRV_NAME,
+	.probe		= cros_ec_hwmon_probe,
+	.id_table	= cros_ec_hwmon_id,
+};
+module_platform_driver(cros_ec_hwmon_driver);
+
+MODULE_DEVICE_TABLE(platform, cros_ec_hwmon_id);
+MODULE_DESCRIPTION("ChromeOS EC Hardware Monitoring Driver");
+MODULE_AUTHOR("Thomas Weißschuh <linux@weissschuh.net");
+MODULE_LICENSE("GPL");