ACPI: fan: Workaround for 64-bit firmware bug

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[ Upstream commit 2e00f7a4bb ]

Some firmware implementations use the "Ones" ASL opcode to produce
an integer with all bits set in order to indicate missing speed or
power readings. This however only works when using 32-bit integers,
as the ACPI spec requires a 32-bit integer (0xFFFFFFFF) to be
returned for missing speed/power readings. With 64-bit integers the
"Ones" opcode produces a 64-bit integer with all bits set, violating
the ACPI spec regarding the placeholder value for missing readings.

Work around such buggy firmware implementation by also checking for
64-bit integers with all bits set when reading _FST.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
[ rjw: Typo fix in the changelog ]
Link: https://patch.msgid.link/20251007234149.2769-3-W_Armin@gmx.de
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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Armin Wolf 2025-10-08 01:41:45 +02:00 • committed by Greg Kroah-Hartman

parent 3d9ecabe29

commit f916f071e4

2 changed files with 36 additions and 7 deletions

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33

drivers/acpi/fan.h

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10

drivers/acpi/fan_hwmon.c

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