ACPICA: Hardcode access width for the reset register.

The ACPI spec requires the reset register width to be 8, so we
now hardcode it and ignore the FADT value. This provides/maintains
compatibility with other ACPI implementations that have allowed
BIOS code with bad register width values to go unnoticed.
Matthew Garett, Bob Moore, Lv Zheng.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 9 insertions, 2 deletions

diff --git a/drivers/acpi/acpica/hwxface.c b/drivers/acpi/acpica/hwxface.c
index f81fb068d20e..d3682c2ae0d1 100644
--- a/drivers/acpi/acpica/hwxface.c
+++ b/drivers/acpi/acpica/hwxface.c
@@ -83,11 +83,17 @@ acpi_status acpi_reset(void)
                  * For I/O space, write directly to the OSL. This bypasses the port
                  * validation mechanism, which may block a valid write to the reset
                  * register.
-                 * Spec section 4.7.3.6 requires register width to be 8.
+                 *
+                 * NOTE:
+                 * The ACPI spec requires the reset register width to be 8, so we
+                 * hardcode it here and ignore the FADT value. This maintains
+                 * compatibility with other ACPI implementations that have allowed
+                 * BIOS code with bad register width values to go unnoticed.
                  */
                 status =
                     acpi_os_write_port((acpi_io_address) reset_reg->address,
-                                       acpi_gbl_FADT.reset_value, 8);
+                                       acpi_gbl_FADT.reset_value,
+                                       ACPI_RESET_REGISTER_WIDTH);
         } else {
                 /* Write the reset value to the reset register */
 
diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
index fed5af2bcb93..63909d9c2f7a 100644
--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -349,6 +349,7 @@ typedef u32 acpi_physical_address;
 #define ACPI_PM1_REGISTER_WIDTH         16
 #define ACPI_PM2_REGISTER_WIDTH         8
 #define ACPI_PM_TIMER_WIDTH             32
+#define ACPI_RESET_REGISTER_WIDTH       8
 
 /* Names within the namespace are 4 bytes long */