Revert "ACPICA: FADT support cleanup"

Pavel Machek reports that commit 6ea8c546f365 (ACPICA: FADT support
cleanup) breaks thermal management on his Thinkpad X60 and T40p, so
revert it.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=187311
Fixes: 6ea8c546f365 (ACPICA: FADT support cleanup)
Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/drivers/acpi/acpica/tbfadt.c b/drivers/acpi/acpica/tbfadt.c
index 046c4d0394ee..5fb838e592dc 100644
--- a/drivers/acpi/acpica/tbfadt.c
+++ b/drivers/acpi/acpica/tbfadt.c
@@ -480,19 +480,17 @@ static void acpi_tb_convert_fadt(void)
         u32 i;
 
         /*
-         * For ACPI 1.0 FADTs (revision 1), ensure that reserved fields which
+         * For ACPI 1.0 FADTs (revision 1 or 2), ensure that reserved fields which
          * should be zero are indeed zero. This will workaround BIOSs that
          * inadvertently place values in these fields.
          *
          * The ACPI 1.0 reserved fields that will be zeroed are the bytes located
          * at offset 45, 55, 95, and the word located at offset 109, 110.
          *
-         * Note: The FADT revision value is unreliable because of BIOS errors.
-         * The table length is instead used as the final word on the version.
-         *
-         * Note: FADT revision 3 is the ACPI 2.0 version of the FADT.
+         * Note: The FADT revision value is unreliable. Only the length can be
+         * trusted.
          */
-        if (acpi_gbl_FADT.header.length <= ACPI_FADT_V3_SIZE) {
+        if (acpi_gbl_FADT.header.length <= ACPI_FADT_V2_SIZE) {
                 acpi_gbl_FADT.preferred_profile = 0;
                 acpi_gbl_FADT.pstate_control = 0;
                 acpi_gbl_FADT.cst_control = 0;