ACPICA: Clear PM register write-only bits on reading

[safe/jmp/linux-2.6] / drivers / acpi / acpica / hwregs.c

diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
index f8ee0a7..7b2fb60 100644 (file)
--- a/drivers/acpi/acpica/hwregs.c
+++ b/drivers/acpi/acpica/hwregs.c
@@ -207,6 +207,13 @@ acpi_hw_register_read(u32 register_id, u32 * return_value)
                                               xpm1a_control_block,
                                               &acpi_gbl_FADT.
                                               xpm1b_control_block);
+
+               /*
+                * Zero the write-only bits. From the ACPI specification, "Hardware
+                * Write-Only Bits": "Upon reads to registers with write-only bits,
+                * software masks out all write-only bits."
+                */
+               value &= ~ACPI_PM1_CONTROL_WRITEONLY_BITS;
                break;
 
        case ACPI_REGISTER_PM2_CONTROL: /* 8-bit access */