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January 27th, 2021 21:00

Linux kernel regression in fan control (dell-smm-hwmon.c) on XPS L502X

This has been deemed a BIOS bug by the linux kernel team:

Quote: The [fan control] feature exists, but each call to it takes way
more time than it should and so causes other kernel tasks to hang. You
can see more details in this kernel bug where the blacklist was

It has been reported[0] that the Dell XPS 15 L502X exhibits similar
freezing behavior to the other systems[1] on this blacklist. The issue
was exposed by a prior change of mine to automatically load
dell_smm_hwmon on a wider set of XPS models. To fix the regression, add
this model to the blacklist.


Fixes: b8a13e5e8f37 ("hwmon: (dell-smm) Use one DMI match for all XPS models")
Reported-by: Bob Hepple 
Tested-by: Bob Hepple
Signed-off-by: Thomas Hebb 

 drivers/hwmon/dell-smm-hwmon.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index ec448f5f2dc3..73b9db9e3aab 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -1159,6 +1159,13 @@ static struct dmi_system_id i8k_blacklist_fan_support_dmi_table[] __initdata = {
                        DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "XPS13 9333"),
+       {
+               .ident = "Dell XPS 15 L502X",
+               .matches = {
+                       DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+                       DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Dell System XPS L502X"),
+               },
+       },
        { }

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