[PATCH 2/3] ACPI: fan: Ignore broken _FST on Samsung Galaxy Book 930XDB

[Leonard Lausen]

FAN0._FST on the Samsung Galaxy Book 930XDB stores the reference
returned by Index() in a local variable and passes that reference to
Add(). ACPICA rejects the operand with AE_AML_OPERAND_TYPE when the fan
is running. The zero-speed path does not execute the faulty Add() and
can succeed.

The Microsoft fan extensions added a notification handler that evaluates
_FST on each fan status change. On this machine, fan notifications now
produce repeated ACPI errors, particularly around s2idle suspend/resume.
Speed telemetry also fails whenever the faulty path is taken.

Ignore _FST on this model. This skips the unusable speed telemetry and
Microsoft notification handling while preserving the legacy firmware fan
control. Match the vendor and full DMI product string,
930XDB/931XDB/930XDY. The firmware was inspected on BIOS
P11RFX.067.230331.SP.

Fixes: a5c2fcd82e04 ("ACPI: fan: Add support for Microsoft fan extensions")
Signed-off-by: Leonard Lausen <leonard@xxxxxxxxx>
---
 drivers/acpi/fan_core.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/fan_core.c b/drivers/acpi/fan_core.c
index 624d0736b581..48a6818e6282 100644
--- a/drivers/acpi/fan_core.c
+++ b/drivers/acpi/fan_core.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/bits.h>
+#include <linux/dmi.h>
 #include <linux/kernel.h>
 #include <linux/limits.h>
 #include <linux/math.h>
@@ -50,6 +51,24 @@ static const struct acpi_device_id fan_device_ids[] = {
 };
 MODULE_DEVICE_TABLE(acpi, fan_device_ids);
 
+/*
+ * The _FST method on these machines stores an Index() reference in a local
+ * variable and then uses that reference as an Add() operand when the fan is
+ * running.  This aborts the method with AE_AML_OPERAND_TYPE.  The Microsoft
+ * fan extensions install a notification handler that evaluates this broken
+ * method on each fan status change, producing repeated ACPI errors.
+ */
+static const struct dmi_system_id acpi_fan_broken_fst_dmi_table[] = {
+	{
+		.ident = "Samsung Galaxy Book 930XDB/931XDB/930XDY",
+		.matches = {
+			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "930XDB/931XDB/930XDY"),
+		},
+	},
+	{}
+};
+
 /* thermal cooling device callbacks */
 static int fan_get_max_state(struct thermal_cooling_device *cdev, unsigned long
 			     *state)
@@ -511,10 +530,14 @@ static int acpi_fan_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, fan);
 
 	if (acpi_has_method(device->handle, "_FST")) {
-		fan->has_fst = true;
-		fan->acpi4 = acpi_has_method(device->handle, "_FIF") &&
-				acpi_has_method(device->handle, "_FPS") &&
-				acpi_has_method(device->handle, "_FSL");
+		if (dmi_check_system(acpi_fan_broken_fst_dmi_table)) {
+			dev_warn(&pdev->dev, FW_BUG "Ignoring broken _FST method\n");
+		} else {
+			fan->has_fst = true;
+			fan->acpi4 = acpi_has_method(device->handle, "_FIF") &&
+					acpi_has_method(device->handle, "_FPS") &&
+					acpi_has_method(device->handle, "_FSL");
+		}
 	}
 
 	if (fan->acpi4) {
-- 
2.55.0