Commit 8636f8d2 authored by Bob Moore's avatar Bob Moore Committed by Len Brown
Browse files

ACPICA: Change handling of PM1 Status register ignored bit

Ignored bits must be preserved according to the ACPI spec.
Usually this means a read/modify/write when writing to the
register.  However, for status registers, writing a one means
clear the event.  Writing a zero means preserve the event (do not
clear.) This behavior is clarified in the ACPI 4.0 spec, and the
ACPICA code now simply always writes a zero to the ignored bit.
Signed-off-by: default avatarBob Moore <>
Signed-off-by: default avatarLin Ming <>
Signed-off-by: default avatarLen Brown <>
parent 8a335a23
......@@ -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,
if (ACPI_FAILURE(status)) {
goto exit;
/* Insert the bits to be preserved */
/* 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.
status = acpi_hw_write_multiple(value,
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