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mb/google/beltino: Fix ACPI fan control FNP4 power resource

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The FNP4 power resource (minimum fan level) had both _ON and _OFF
methods setting the same state (\FLVL = 4), violating ACPI power
resource requirements where _OFF must transition to a state where
_STA eventually returns 0 (OFF).

This violation causes Windows to reject the thermal zone entirely due
to its stricter ACPI compliance checking, resulting in non-functional
fan control. Linux tolerates this bug, which is why it went unnoticed.

Since FAN4 represents the minimum cooling state with no lower state
to transition to, the correct implementation is to make _OFF a no-op.
This maintains proper ACPI state machine semantics: after _ON, _STA
returns 1; after _OFF, the system remains at minimum cooling (which
is already the lowest valid state).

This enables proper fan control operation on Windows while maintaining
Linux compatibility.

TEST=build/boot Win10/Linux on google/beltino, verify fan functional
under Windows 10, continues to work correctly under Linux.

Change-Id: Ie53ad9b547b2f2d522e2ed692f8db55aa9a6b8d3
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/89839
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Matt DeVillier 2025-10-30 15:00:55 -05:00
commit 8a518b2134
1 changed files with 3 additions and 5 deletions
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8
src/mainboard/google/beltino/acpi/thermal.asl
View file

@ -271,11 +271,9 @@ Scope (\_TZ)
}
}
Method (_OFF) {
If (_STA ()) {
\FLVL = 4
\_SB.PCI0.LPCB.SIO.ENVC.F2PS = FAN4_PWM
Notify (\_TZ.THRM, 0x81)
}
// FAN4 is the minimum cooling state (idle/lowest fan speed)
// There is no lower state to transition to, so _OFF is a no-op
// to maintain proper ACPI power resource state machine semantics
}
}