1 files changed, 24 insertions, 9 deletions

diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
index 9c8162128c2b..5a64e577975f 100644
--- a/drivers/acpi/acpica/hwregs.c
+++ b/drivers/acpi/acpica/hwregs.c
@@ -372,9 +372,17 @@ acpi_hw_read_multiple(u32 *value,
                 }
         }
 
-        /* Shift the B bits above the A bits */
-
-        *value = value_a | (value_b << register_a->bit_width);
+        /*
+         * OR the two return values together. No shifting or masking is necessary,
+         * because of how the PM1 registers are defined in the ACPI specification:
+         *
+         * "Although the bits can be split between the two register blocks (each
+         * register block has a unique pointer within the FADT), the bit positions
+         * are maintained. The register block with unimplemented bits (that is,
+         * those implemented in the other register block) always returns zeros,
+         * and writes have no side effects"
+         */
+        *value = (value_a | value_b);
         return (AE_OK);
 }
 
@@ -406,13 +414,20 @@ acpi_hw_write_multiple(u32 value,
                 return (status);
         }
 
-        /* Second register is optional */
-
+        /*
+         * Second register is optional
+         *
+         * No bit shifting or clearing is necessary, because of how the PM1
+         * registers are defined in the ACPI specification:
+         *
+         * "Although the bits can be split between the two register blocks (each
+         * register block has a unique pointer within the FADT), the bit positions
+         * are maintained. The register block with unimplemented bits (that is,
+         * those implemented in the other register block) always returns zeros,
+         * and writes have no side effects"
+         */
         if (register_b->address) {
-
-                /* Normalize the B bits before write */
-
-                status = acpi_write(value >> register_a->bit_width, register_b);
+                status = acpi_write(value, register_b);
         }
 
         return (status);