1 files changed, 12 insertions, 5 deletions

diff --git a/drivers/acpi/executer/exprep.c b/drivers/acpi/executer/exprep.c
index 7719ae5d4f16..916234bf811c 100644
--- a/drivers/acpi/executer/exprep.c
+++ b/drivers/acpi/executer/exprep.c
@@ -519,13 +519,20 @@ acpi_status acpi_ex_prep_field_value(struct acpi_create_field_info *info)
                 acpi_ut_add_reference(obj_desc->index_field.index_obj);
 
                 /*
+                 * February 2006: Changed to match MS behavior
+                 *
                  * The value written to the Index register is the byte offset of the
-                 * target field
-                 * Note: may change code to: ACPI_DIV_8 (Info->field_bit_position)
+                 * target field.
+                 *
+                 * Previously, the value was calculated as an index in terms of the
+                 * width of the Data register, as below:
+                 *
+                 *   obj_desc->index_field.Value = (u32)
+                 *       (Info->field_bit_position / ACPI_MUL_8 (
+                 *           obj_desc->Field.access_byte_width));
                  */
-                obj_desc->index_field.value = (u32)
-                    (info->field_bit_position /
-                     ACPI_MUL_8(obj_desc->field.access_byte_width));
+                obj_desc->index_field.value =
+                    (u32) ACPI_DIV_8(info->field_bit_position);
 
                 ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,
                                   "index_field: bit_off %X, Off %X, Value %X, Gran %X, Index %p, Data %p\n",