ACPI: fan: Add hwmon support

Currently, the driver does only support a custom sysfs
interface to allow userspace to read the fan speed.
Add support for the standard hwmon interface so users
can read the fan speed with standard tools like "sensors".

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/Makefile

@@ -77,6 +77,7 @@ obj-$(CONFIG_ACPI_TINY_POWER_BUTTON)	+= tiny-power-button.o
 obj-$(CONFIG_ACPI_FAN)		+= fan.o
 fan-objs			:= fan_core.o
 fan-objs			+= fan_attr.o
+fan-$(CONFIG_HWMON)		+= fan_hwmon.o
 
 obj-$(CONFIG_ACPI_VIDEO)	+= video.o
 obj-$(CONFIG_ACPI_TAD)		+= acpi_tad.o

drivers/acpi/fan.h

@@ -10,6 +10,8 @@
 #ifndef _ACPI_FAN_H_
 #define _ACPI_FAN_H_
 
+#include <linux/kconfig.h>
+
 #define ACPI_FAN_DEVICE_IDS	\
 	{"INT3404", }, /* Fan */ \
 	{"INTC1044", }, /* Fan for Tiger Lake generation */ \
@@ -57,4 +59,11 @@ struct acpi_fan {
 int acpi_fan_get_fst(struct acpi_device *device, struct acpi_fan_fst *fst);
 int acpi_fan_create_attributes(struct acpi_device *device);
 void acpi_fan_delete_attributes(struct acpi_device *device);
+
+#if IS_REACHABLE(CONFIG_HWMON)
+int devm_acpi_fan_create_hwmon(struct acpi_device *device);
+#else
+static inline int devm_acpi_fan_create_hwmon(struct acpi_device *device) { return 0; };
+#endif
+
 #endif

drivers/acpi/fan_core.c

@@ -336,6 +336,10 @@ static int acpi_fan_probe(struct platform_device *pdev)
 		if (result)
 			return result;
 
+		result = devm_acpi_fan_create_hwmon(device);
+		if (result)
+			return result;
+
 		result = acpi_fan_create_attributes(device);
 		if (result)
 			return result;

drivers/acpi/fan_hwmon.c

@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hwmon interface for the ACPI Fan driver.
+ *
+ * Copyright (C) 2024 Armin Wolf <W_Armin@gmx.de>
+ */
+
+#include <linux/acpi.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/limits.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include "fan.h"
+
+/* Returned when the ACPI fan does not support speed reporting */
+#define FAN_SPEED_UNAVAILABLE	U32_MAX
+#define FAN_POWER_UNAVAILABLE	U32_MAX
+
+static struct acpi_fan_fps *acpi_fan_get_current_fps(struct acpi_fan *fan, u64 control)
+{
+	unsigned int i;
+
+	for (i = 0; i < fan->fps_count; i++) {
+		if (fan->fps[i].control == control)
+			return &fan->fps[i];
+	}
+
+	return NULL;
+}
+
+static umode_t acpi_fan_hwmon_is_visible(const void *drvdata, enum hwmon_sensor_types type,
+					 u32 attr, int channel)
+{
+	const struct acpi_fan *fan = drvdata;
+	unsigned int i;
+
+	switch (type) {
+	case hwmon_fan:
+		switch (attr) {
+		case hwmon_fan_input:
+			return 0444;
+		case hwmon_fan_target:
+			/*
+			 * When in fine grain control mode, not every fan control value
+			 * has an associated fan performance state.
+			 */
+			if (fan->fif.fine_grain_ctrl)
+				return 0;
+
+			return 0444;
+		default:
+			return 0;
+		}
+	case hwmon_power:
+		switch (attr) {
+		case hwmon_power_input:
+			/*
+			 * When in fine grain control mode, not every fan control value
+			 * has an associated fan performance state.
+			 */
+			if (fan->fif.fine_grain_ctrl)
+				return 0;
+
+			/*
+			 * When all fan performance states contain no valid power data,
+			 * when the associated attribute should not be created.
+			 */
+			for (i = 0; i < fan->fps_count; i++) {
+				if (fan->fps[i].power != FAN_POWER_UNAVAILABLE)
+					return 0444;
+			}
+
+			return 0;
+		default:
+			return 0;
+		}
+	default:
+		return 0;
+	}
+}
+
+static int acpi_fan_hwmon_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
+			       int channel, long *val)
+{
+	struct acpi_device *adev = to_acpi_device(dev->parent);
+	struct acpi_fan *fan = dev_get_drvdata(dev);
+	struct acpi_fan_fps *fps;
+	struct acpi_fan_fst fst;
+	int ret;
+
+	ret = acpi_fan_get_fst(adev, &fst);
+	if (ret < 0)
+		return ret;
+
+	switch (type) {
+	case hwmon_fan:
+		switch (attr) {
+		case hwmon_fan_input:
+			if (fst.speed == FAN_SPEED_UNAVAILABLE)
+				return -ENODEV;
+
+			if (fst.speed > LONG_MAX)
+				return -EOVERFLOW;
+
+			*val = fst.speed;
+			return 0;
+		case hwmon_fan_target:
+			fps = acpi_fan_get_current_fps(fan, fst.control);
+			if (!fps)
+				return -EIO;
+
+			if (fps->speed > LONG_MAX)
+				return -EOVERFLOW;
+
+			*val = fps->speed;
+			return 0;
+		default:
+			return -EOPNOTSUPP;
+		}
+	case hwmon_power:
+		switch (attr) {
+		case hwmon_power_input:
+			fps = acpi_fan_get_current_fps(fan, fst.control);
+			if (!fps)
+				return -EIO;
+
+			if (fps->power == FAN_POWER_UNAVAILABLE)
+				return -ENODEV;
+
+			if (fps->power > LONG_MAX / MICROWATT_PER_MILLIWATT)
+				return -EOVERFLOW;
+
+			*val = fps->power * MICROWATT_PER_MILLIWATT;
+			return 0;
+		default:
+			return -EOPNOTSUPP;
+		}
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const struct hwmon_ops acpi_fan_hwmon_ops = {
+	.is_visible = acpi_fan_hwmon_is_visible,
+	.read = acpi_fan_hwmon_read,
+};
+
+static const struct hwmon_channel_info * const acpi_fan_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_TARGET),
+	HWMON_CHANNEL_INFO(power, HWMON_P_INPUT),
+	NULL
+};
+
+static const struct hwmon_chip_info acpi_fan_hwmon_chip_info = {
+	.ops = &acpi_fan_hwmon_ops,
+	.info = acpi_fan_hwmon_info,
+};
+
+int devm_acpi_fan_create_hwmon(struct acpi_device *device)
+{
+	struct acpi_fan *fan = acpi_driver_data(device);
+	struct device *hdev;
+
+	hdev = devm_hwmon_device_register_with_info(&device->dev, "acpi_fan", fan,
+						    &acpi_fan_hwmon_chip_info, NULL);
+	return PTR_ERR_OR_ZERO(hdev);
+}