diff options
| -rw-r--r-- | drivers/acpi/acpica/hwregs.c | 27 |
1 files changed, 11 insertions, 16 deletions
diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c index edc627c9fc0..fd7abe277db 100644 --- a/drivers/acpi/acpica/hwregs.c +++ b/drivers/acpi/acpica/hwregs.c @@ -273,22 +273,17 @@ acpi_status acpi_hw_register_write(u32 register_id, u32 value) switch (register_id) { case ACPI_REGISTER_PM1_STATUS: /* PM1 A/B: 16-bit access each */ - - /* Perform a read first to preserve certain bits (per ACPI spec) */ - - status = acpi_hw_read_multiple(&read_value, - &acpi_gbl_xpm1a_status, - &acpi_gbl_xpm1b_status); - if (ACPI_FAILURE(status)) { - goto exit; - } - - /* Insert the bits to be preserved */ - - ACPI_INSERT_BITS(value, ACPI_PM1_STATUS_PRESERVED_BITS, - read_value); - - /* Now we can write the data */ + /* + * Handle the "ignored" bit in PM1 Status. According to the ACPI + * specification, ignored bits are to be preserved when writing. + * Normally, this would mean a read/modify/write sequence. However, + * preserving a bit in the status register is different. Writing a + * one clears the status, and writing a zero preserves the status. + * Therefore, we must always write zero to the ignored bit. + * + * This behavior is clarified in the ACPI 4.0 specification. + */ + value &= ~ACPI_PM1_STATUS_PRESERVED_BITS; status = acpi_hw_write_multiple(value, &acpi_gbl_xpm1a_status, |