Change in coreboot[master]: drivers/intel/gma: Fix OpRegion Mailbox3 synchronization

[Nico Huber (Code Review)]

Nico Huber has uploaded this change for review. ( https://review.coreboot.org/28302

Change subject: drivers/intel/gma: Fix OpRegion Mailbox3 synchronization
......................................................................

drivers/intel/gma: Fix OpRegion Mailbox3 synchronization

Make XBCM `Serialized` (obvious), and check for the callee clearing the
request bit (we checked only the status for 0 which we potentially wrote
ourselves).

Change-Id: Ic92d525eda8d0a159fa5ddaacf230658d71c1578
Signed-off-by: Nico Huber 
---
M src/drivers/intel/gma/acpi/configure_brightness_levels.asl
1 file changed, 9 insertions(+), 4 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/02/28302/1

diff --git a/src/drivers/intel/gma/acpi/configure_brightness_levels.asl b/src/drivers/intel/gma/acpi/configure_brightness_levels.asl
index 024360f..951d33d 100644
--- a/src/drivers/intel/gma/acpi/configure_brightness_levels.asl
+++ b/src/drivers/intel/gma/acpi/configure_brightness_levels.asl
@@ -55,7 +55,7 @@
    	 *         * Driver not loaded or not ready
    	 *         * Driver reported an error during ASLE IRQ
    	 */
-		Method (XBCM, 1, NotSerialized)
+		Method (XBCM, 1, Serialized)
    	{
    		If (LEqual(ASLS, Zero))
    		{
@@ -84,9 +84,14 @@
    		While (LGreater(Local0, Zero))
    		{
    			Sleep (1)
-				If (LEqual(And(ShiftRight(ASLC, 12), 0x3), Zero))
-				{
-					Return (Zero)
+				If (LEqual (And (ASLC, 0x2), 0)) {
+					/* Request has been processed, check status: */
+					And (ShiftRight (ASLC, 12), 0x3, Local1)
+					If (LEqual (Local1, 0)) {
+						Return (0)
+					} Else {
+						Return (Ones)
+					}
    			}
    			Decrement (Local0)
    		}