https://bugzilla.kernel.org/show_bug.cgi?id=219643
Eduard Christian Dumitrescu (eduard.c.dumitre...@gmail.com) changed:
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CC| |eduard.c.dumitrescu@gmail.c
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--- Comment #4 from Eduard Christian Dumitrescu (eduard.c.dumitre...@gmail.com)
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I have performed the bisection. The bug was introduced in commit
57d0557dfa4940919ec2971245a6d288e5d85aa8 which adds a new fan control method
via the FANG and FANW ACPI methods. In particular, have a look at the
`fan_init` method.
The T495s laptop has the FANG+FANW ACPI methods (therefore `fang_handle!=NULL`
and `fanw_handle!=NULL`) but they do not actually work, which results in the
dreaded "No such device or address" error. Fan access and control is restored
after forcing the legacy non-ACPI fan control method by setting both
`fang_handle` and `fanw_handle` to NULL.
I speculate that the underlying cause is related to the following dmesg line:
thinkpad_acpi: secondary fan control detected & enabled
The DSDT table code for the FANG+FANW methods doesn't seem to do anything
special regarding the fan being secondary, but I am not an ACPI expert. I will
attach the relevant dump file anyway. I also note that the current
thinkpad_acpi module FANG+FANW code does not handle secondary fans in any way.
Finally, I am attaching my patch which adds a quirk for T495 and T495s to make
them avoid the FANG/FANW methods.
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