ACPI: fan: Add fan speed reporting for fans with only _FST

Add support for ACPI fans with _FST to report their speed even if they do
not support fan control.

As suggested by Armin Wolf [1] and per the Windows Thermal Management
Design Guide [2], Samsung Galaxy Book series devices (and possibly many
more devices where the Windows guide was strictly followed) only implement
the _FST method and do not support ACPI-based fan control.

Currently, these fans are not supported by the kernel driver but this patch
will make some very small adjustments to allow them to be supported.

This patch is tested and working for me on a Samsung Galaxy Book2 Pro whose
DSDT (and several other Samsung Galaxy Book series notebooks which
currently have the same issue) can be found at [3].

Link: https://lore.kernel.org/platform-driver-x86/53c5075b-1967-45d0-937f-463912dd966d@gmx.de [1]
Link: https://learn.microsoft.com/en-us/windows-hardware/design/device-experiences/design-guide [2]
Link: https://github.com/joshuagrisham/samsung-galaxybook-extras/tree/8e3087a06b8bdcdfdd081367af4b744a56cc4ee9/dsdt [3]

Signed-off-by: Joshua Grisham <josh@joshuagrisham.com>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20250222094407.9753-1-josh@joshuagrisham.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: joshuagrisham

drivers/acpi/fan.h

@@ -49,6 +49,7 @@ struct acpi_fan_fst {
 
 struct acpi_fan {
 	bool acpi4;
+	bool has_fst;
 	struct acpi_fan_fif fif;
 	struct acpi_fan_fps *fps;
 	int fps_count;

drivers/acpi/fan_attr.c

@@ -75,15 +75,6 @@ int acpi_fan_create_attributes(struct acpi_device *device)
 	struct acpi_fan *fan = acpi_driver_data(device);
 	int i, status;
 
-	sysfs_attr_init(&fan->fine_grain_control.attr);
-	fan->fine_grain_control.show = show_fine_grain_control;
-	fan->fine_grain_control.store = NULL;
-	fan->fine_grain_control.attr.name = "fine_grain_control";
-	fan->fine_grain_control.attr.mode = 0444;
-	status = sysfs_create_file(&device->dev.kobj, &fan->fine_grain_control.attr);
-	if (status)
-		return status;
-
 	/* _FST is present if we are here */
 	sysfs_attr_init(&fan->fst_speed.attr);
 	fan->fst_speed.show = show_fan_speed;
@@ -92,7 +83,19 @@ int acpi_fan_create_attributes(struct acpi_device *device)
 	fan->fst_speed.attr.mode = 0444;
 	status = sysfs_create_file(&device->dev.kobj, &fan->fst_speed.attr);
 	if (status)
-		goto rem_fine_grain_attr;
+		return status;
+
+	if (!fan->acpi4)
+		return 0;
+
+	sysfs_attr_init(&fan->fine_grain_control.attr);
+	fan->fine_grain_control.show = show_fine_grain_control;
+	fan->fine_grain_control.store = NULL;
+	fan->fine_grain_control.attr.name = "fine_grain_control";
+	fan->fine_grain_control.attr.mode = 0444;
+	status = sysfs_create_file(&device->dev.kobj, &fan->fine_grain_control.attr);
+	if (status)
+		goto rem_fst_attr;
 
 	for (i = 0; i < fan->fps_count; ++i) {
 		struct acpi_fan_fps *fps = &fan->fps[i];
@@ -109,18 +112,18 @@ int acpi_fan_create_attributes(struct acpi_device *device)
 
 			for (j = 0; j < i; ++j)
 				sysfs_remove_file(&device->dev.kobj, &fan->fps[j].dev_attr.attr);
-			goto rem_fst_attr;
+			goto rem_fine_grain_attr;
 		}
 	}
 
 	return 0;
 
-rem_fst_attr:
-	sysfs_remove_file(&device->dev.kobj, &fan->fst_speed.attr);
-
 rem_fine_grain_attr:
 	sysfs_remove_file(&device->dev.kobj, &fan->fine_grain_control.attr);
 
+rem_fst_attr:
+	sysfs_remove_file(&device->dev.kobj, &fan->fst_speed.attr);
+
 	return status;
 }
 
@@ -129,9 +132,13 @@ void acpi_fan_delete_attributes(struct acpi_device *device)
 	struct acpi_fan *fan = acpi_driver_data(device);
 	int i;
 
+	sysfs_remove_file(&device->dev.kobj, &fan->fst_speed.attr);
+
+	if (!fan->acpi4)
+		return;
+
 	for (i = 0; i < fan->fps_count; ++i)
 		sysfs_remove_file(&device->dev.kobj, &fan->fps[i].dev_attr.attr);
 
-	sysfs_remove_file(&device->dev.kobj, &fan->fst_speed.attr);
 	sysfs_remove_file(&device->dev.kobj, &fan->fine_grain_control.attr);
 }

drivers/acpi/fan_core.c

@@ -203,12 +203,16 @@ static const struct thermal_cooling_device_ops fan_cooling_ops = {
  * --------------------------------------------------------------------------
 */
 
+static bool acpi_fan_has_fst(struct acpi_device *device)
+{
+	return acpi_has_method(device->handle, "_FST");
+}
+
 static bool acpi_fan_is_acpi4(struct acpi_device *device)
 {
 	return acpi_has_method(device->handle, "_FIF") &&
 	       acpi_has_method(device->handle, "_FPS") &&
-	       acpi_has_method(device->handle, "_FSL") &&
-	       acpi_has_method(device->handle, "_FST");
+	       acpi_has_method(device->handle, "_FSL");
 }
 
 static int acpi_fan_get_fif(struct acpi_device *device)
@@ -327,25 +331,32 @@ static int acpi_fan_probe(struct platform_device *pdev)
 	device->driver_data = fan;
 	platform_set_drvdata(pdev, fan);
 
-	if (acpi_fan_is_acpi4(device)) {
+	if (acpi_fan_has_fst(device)) {
+		fan->has_fst = true;
+		fan->acpi4 = acpi_fan_is_acpi4(device);
+	}
+
+	if (fan->acpi4) {
 		result = acpi_fan_get_fif(device);
 		if (result)
 			return result;
 
 		result = acpi_fan_get_fps(device);
 		if (result)
 			return result;
+	}
 
+	if (fan->has_fst) {
 		result = devm_acpi_fan_create_hwmon(device);
 		if (result)
 			return result;
 
 		result = acpi_fan_create_attributes(device);
 		if (result)
 			return result;
+	}
 
-		fan->acpi4 = true;
-	} else {
+	if (!fan->acpi4) {
 		result = acpi_device_update_power(device, NULL);
 		if (result) {
 			dev_err(&device->dev, "Failed to set initial power state\n");
@@ -391,7 +402,7 @@ static int acpi_fan_probe(struct platform_device *pdev)
 err_unregister:
 	thermal_cooling_device_unregister(cdev);
 err_end:
-	if (fan->acpi4)
+	if (fan->has_fst)
 		acpi_fan_delete_attributes(device);
 
 	return result;
@@ -401,7 +412,7 @@ static void acpi_fan_remove(struct platform_device *pdev)
 {
 	struct acpi_fan *fan = platform_get_drvdata(pdev);
 
-	if (fan->acpi4) {
+	if (fan->has_fst) {
 		struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
 
 		acpi_fan_delete_attributes(device);

drivers/acpi/fan_hwmon.c

@@ -43,6 +43,10 @@ static umode_t acpi_fan_hwmon_is_visible(const void *drvdata, enum hwmon_sensor_
 		case hwmon_fan_input:
 			return 0444;
 		case hwmon_fan_target:
+			/* Only acpi4 fans support fan control. */
+			if (!fan->acpi4)
+				return 0;
+
 			/*
 			 * When in fine grain control mode, not every fan control value
 			 * has an associated fan performance state.
@@ -57,6 +61,10 @@ static umode_t acpi_fan_hwmon_is_visible(const void *drvdata, enum hwmon_sensor_
 	case hwmon_power:
 		switch (attr) {
 		case hwmon_power_input:
+			/* Only acpi4 fans support fan control. */
+			if (!fan->acpi4)
+				return 0;
+
 			/*
 			 * When in fine grain control mode, not every fan control value
 			 * has an associated fan performance state.