[PATCH 43/98] ACPICA: Change handling of PM1 Status register ignored bit

Len Brown
2009-03-28T04:32:55Z

From: Bob Moore <robert.moore@intel.com>

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: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
---
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 edc627c..fd7abe2 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,
--
1.6.0.6