From: Bob Moore <robert.moore@xxxxxxxxx>
The revision number in the FADT has been found to be completely
unreliable and cannot be trusted. Only the table length can be
used to infer the actual version.
Signed-off-by: Bob Moore <robert.moore@xxxxxxxxx>
Signed-off-by: Lin Ming <ming.m.lin@xxxxxxxxx>
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
---
drivers/acpi/acpica/tbfadt.c | 5 ++++-
include/acpi/actbl.h | 16 ++++++++++++++++
2 files changed, 20 insertions(+), 1 deletions(-)
diff --git a/drivers/acpi/acpica/tbfadt.c b/drivers/acpi/acpica/tbfadt.c
index 428d44e..6f5588e 100644
--- a/drivers/acpi/acpica/tbfadt.c
+++ b/drivers/acpi/acpica/tbfadt.c
@@ -384,8 +384,11 @@ static void acpi_tb_convert_fadt(void)
*
* 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. Only the length can be
+ * trusted.
*/
- if (acpi_gbl_FADT.header.revision < FADT2_REVISION_ID) {
+ 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;
diff --git a/include/acpi/actbl.h b/include/acpi/actbl.h
index 7e42bfe..d41c948 100644
--- a/include/acpi/actbl.h
+++ b/include/acpi/actbl.h
@@ -343,4 +343,20 @@ struct acpi_table_desc {
#include <acpi/actbl1.h>
#include <acpi/actbl2.h>
+/*
+ * Sizes of the various flavors of FADT. We need to look closely
+ * at the FADT length because the version number essentially tells
+ * us nothing because of many BIOS bugs where the version does not
+ * match the expected length. In other words, the length of the
+ * FADT is the bottom line as to what the version really is.
+ *
+ * For reference, the values below are as follows:
+ * FADT V1 size: 0x74
+ * FADT V2 size: 0x84
+ * FADT V3+ size: 0xF4
+ */
+#define ACPI_FADT_V1_SIZE (u32) (ACPI_FADT_OFFSET (flags) + 4)
+#define ACPI_FADT_V2_SIZE (u32) (ACPI_FADT_OFFSET (reserved4[0]) + 3)
+#define ACPI_FADT_V3_SIZE (u32) (sizeof (struct acpi_table_fadt))
+
#endif /* __ACTBL_H__ */
--
1.7.4.1.343.ga91df
--
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