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>

1 files changed, 18 insertions, 7 deletions

diff --git a/drivers/acpi/fan_core.c b/drivers/acpi/fan_core.c
index 10016f52f4f4..8ad12ad3aaaf 100644
--- a/drivers/acpi/fan_core.c
+++ b/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)
@@ -327,7 +331,12 @@ 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;
@@ -335,7 +344,9 @@ static int acpi_fan_probe(struct platform_device *pdev)
 		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;
@@ -343,9 +354,9 @@ static int acpi_fan_probe(struct platform_device *pdev)
 		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 @@ err_remove_link:
 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);