ACPI: Add hack to avoid IASL warning when reading back registers

Upcoming versions of IASL give a warning about unused methods.  This
adds an operation after the read to use the local variable and avoid
the warning.

The warning can be completely disabled on the command line, but as it
can find real issues, my preference is to not do that.

Fixes warnings:
dsdt.aml 640: 		           Store (CTMP, Local0)
Warning  3144 - Method Local is set but never used ^  (Local0)

Change-Id: If55bb8e03abb8861e1f2f08a8bcb1be8c9783afe
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12704
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

1 files changed, 16 insertions, 4 deletions

diff --git a/src/southbridge/intel/lynxpoint/acpi/serialio.asl b/src/southbridge/intel/lynxpoint/acpi/serialio.asl
index 13732f645c..930a8eea27 100644
--- a/src/southbridge/intel/lynxpoint/acpi/serialio.asl
+++ b/src/southbridge/intel/lynxpoint/acpi/serialio.asl
@@ -219,14 +219,20 @@ Device (I2C0)
 	Method (_PS0, 0, Serialized)
 	{
 		And (^PSAT, 0xfffffffc, ^PSAT)
-		Store (^PSAT, Local0)
+		Store (^PSAT, Local0) // Read back after writing
+
+		// Use Local0 to avoid iasl warning: Method Local is set but never used
+		And(Local0, Ones, Local0)
 	}
 
 	// Put controller in D3Hot state
 	Method (_PS3, 0, Serialized)
 	{
 		Or (^PSAT, 0x00000003, ^PSAT)
-		Store (^PSAT, Local0)
+		Store (^PSAT, Local0) // Read back after writing
+
+		// Use Local0 to avoid iasl warning: Method Local is set but never used
+		And(Local0, Ones, Local0)
 	}
 }
 
@@ -292,14 +298,20 @@ Device (I2C1)
 	Method (_PS0, 0, Serialized)
 	{
 		And (^PSAT, 0xfffffffc, ^PSAT)
-		Store (^PSAT, Local0)
+		Store (^PSAT, Local0) // Read back after writing
+
+		// Use Local0 to avoid iasl warning: Method Local is set but never used
+		And(Local0, Ones, Local0)
 	}
 
 	// Put controller in D3Hot state
 	Method (_PS3, 0, Serialized)
 	{
 		Or (^PSAT, 0x00000003, ^PSAT)
-		Store (^PSAT, Local0)
+		Store (^PSAT, Local0) // Read back after writing
+
+		// Use Local0 to avoid iasl warning: Method Local is set but never used
+		And(Local0, Ones, Local0)
 	}
 }