diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
index 2bc3425d3b6a..50b90707d755 100644
--- a/drivers/acpi/acpica/hwregs.c
+++ b/drivers/acpi/acpica/hwregs.c
@@ -52,7 +52,8 @@ ACPI_MODULE_NAME("hwregs")
 #if (!ACPI_REDUCED_HARDWARE)
 /* Local Prototypes */
 static u8
-acpi_hw_get_access_bit_width(struct acpi_generic_address *reg,
+acpi_hw_get_access_bit_width(u64 address,
+			     struct acpi_generic_address *reg,
 			     u8 max_bit_width);
 
 static acpi_status
@@ -71,7 +72,8 @@ acpi_hw_write_multiple(u32 value,
  *
  * FUNCTION:    acpi_hw_get_access_bit_width
  *
- * PARAMETERS:  reg                 - GAS register structure
+ * PARAMETERS:  address             - GAS register address
+ *              reg                 - GAS register structure
  *              max_bit_width       - Max bit_width supported (32 or 64)
  *
  * RETURN:      Status
@@ -81,27 +83,59 @@ acpi_hw_write_multiple(u32 value,
  ******************************************************************************/
 
 static u8
-acpi_hw_get_access_bit_width(struct acpi_generic_address *reg, u8 max_bit_width)
+acpi_hw_get_access_bit_width(u64 address,
+			     struct acpi_generic_address *reg, u8 max_bit_width)
 {
-	if (!reg->access_width) {
-		if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
-			max_bit_width = 32;
-		}
+	u8 access_bit_width;
 
-		/*
-		 * Detect old register descriptors where only the bit_width field
-		 * makes senses.
-		 */
-		if (reg->bit_width < max_bit_width &&
-		    !reg->bit_offset && reg->bit_width &&
-		    ACPI_IS_POWER_OF_TWO(reg->bit_width) &&
-		    ACPI_IS_ALIGNED(reg->bit_width, 8)) {
-			return (reg->bit_width);
-		}
-		return (max_bit_width);
+	/*
+	 * GAS format "register", used by FADT:
+	 *  1. Detected if bit_offset is 0 and bit_width is 8/16/32/64;
+	 *  2. access_size field is ignored and bit_width field is used for
+	 *     determining the boundary of the IO accesses.
+	 * GAS format "region", used by APEI registers:
+	 *  1. Detected if bit_offset is not 0 or bit_width is not 8/16/32/64;
+	 *  2. access_size field is used for determining the boundary of the
+	 *     IO accesses;
+	 *  3. bit_offset/bit_width fields are used to describe the "region".
+	 *
+	 * Note: This algorithm assumes that the "Address" fields should always
+	 *       contain aligned values.
+	 */
+	if (!reg->bit_offset && reg->bit_width &&
+	    ACPI_IS_POWER_OF_TWO(reg->bit_width) &&
+	    ACPI_IS_ALIGNED(reg->bit_width, 8)) {
+		access_bit_width = reg->bit_width;
+	} else if (reg->access_width) {
+		access_bit_width = (1 << (reg->access_width + 2));
 	} else {
-		return (1 << (reg->access_width + 2));
+		access_bit_width =
+		    ACPI_ROUND_UP_POWER_OF_TWO_8(reg->bit_offset +
+						 reg->bit_width);
+		if (access_bit_width <= 8) {
+			access_bit_width = 8;
+		} else {
+			while (!ACPI_IS_ALIGNED(address, access_bit_width >> 3)) {
+				access_bit_width >>= 1;
+			}
+		}
 	}
+
+	/* Maximum IO port access bit width is 32 */
+
+	if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
+		max_bit_width = 32;
+	}
+
+	/*
+	 * Return access width according to the requested maximum access bit width,
+	 * as the caller should know the format of the register and may enforce
+	 * a 32-bit accesses.
+	 */
+	if (access_bit_width < max_bit_width) {
+		return (access_bit_width);
+	}
+	return (max_bit_width);
 }
 
 /******************************************************************************
@@ -163,7 +197,8 @@ acpi_hw_validate_register(struct acpi_generic_address *reg,
 
 	/* Validate the bit_width, convert access_width into number of bits */
 
-	access_width = acpi_hw_get_access_bit_width(reg, max_bit_width);
+	access_width =
+	    acpi_hw_get_access_bit_width(*address, reg, max_bit_width);
 	bit_width =
 	    ACPI_ROUND_UP(reg->bit_offset + reg->bit_width, access_width);
 	if (max_bit_width < bit_width) {
@@ -219,7 +254,7 @@ acpi_status acpi_hw_read(u32 *value, struct acpi_generic_address *reg)
 	 * into number of bits based
 	 */
 	*value = 0;
-	access_width = acpi_hw_get_access_bit_width(reg, 32);
+	access_width = acpi_hw_get_access_bit_width(address, reg, 32);
 	bit_width = reg->bit_offset + reg->bit_width;
 	bit_offset = reg->bit_offset;
 
@@ -311,7 +346,7 @@ acpi_status acpi_hw_write(u32 value, struct acpi_generic_address *reg)
 
 	/* Convert access_width into number of bits based */
 
-	access_width = acpi_hw_get_access_bit_width(reg, 32);
+	access_width = acpi_hw_get_access_bit_width(address, reg, 32);
 	bit_width = reg->bit_offset + reg->bit_width;
 	bit_offset = reg->bit_offset;