drivers/intel/gma/acpi: Reduce display switching stubs

_DCS, _DGS and _DSS are required by specification. However,
we never implemented them properly, and no OS driver com-
plained yet. So we stub them out and keep the traditional
behavior in case an OS driver checks for their existence.

The old implementations also only returned static values as
there never was any write to their GNVS variables. The TRAP()
that was called in one place is actually implemented by some
ThinkPad's SMI handler as docking event. However, as the call
precedes these SMI handlers in coreboot history, it's most
likely an accident.

Change-Id: Ib0b9fcdd58df254d3b2290900e3bc206a7abd92d
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39726
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

1 files changed, 20 insertions, 21 deletions

diff --git a/src/drivers/intel/gma/acpi.c b/src/drivers/intel/gma/acpi.c
index 3f71a5ea84..d3fb69dec8 100644
--- a/src/drivers/intel/gma/acpi.c
+++ b/src/drivers/intel/gma/acpi.c
@@ -102,39 +102,38 @@ drivers_intel_gma_displays_ssdt_generate(const struct i915_gpu_controller_info *
 		}
 
 		/*
-		Method(_DCS, 0)
-		{
-			Return (^^XDCS(<device number>))
-		}
+		 * _DCS, _DGS and _DSS are required by specification. However,
+		 * we never implemented them properly, and no OS driver com-
+		 * plained yet. So we stub them out and keep the traditional
+		 * behavior in case an OS driver checks for their existence.
+		 */
+
+		/*
+		  Method(_DCS, 0)
+		  {
+			Return (0x1d)
+		  }
 		*/
 		acpigen_write_method("_DCS", 0);
-		acpigen_emit_byte(0xa4); /* ReturnOp.  */
-		acpigen_emit_namestring("^^XDCS");
-		acpigen_write_byte(i);
+		acpigen_write_return_integer(0x1d);
 		acpigen_pop_len();
 
 		/*
-		Method(_DGS, 0)
-		{
-			Return (^^XDGS(<device number>))
-		}
+		  Method(_DGS, 0)
+		  {
+			Return (0)
+		  }
 		*/
 		acpigen_write_method("_DGS", 0);
-		acpigen_emit_byte(0xa4); /* ReturnOp.  */
-		acpigen_emit_namestring("^^XDGS");
-		acpigen_write_byte(i);
+		acpigen_write_return_integer(0);
 		acpigen_pop_len();
 
 		/*
-		Method(_DSS, 1)
-		{
-			^^XDSS(0x5a, Arg0)
-		}
+		  Method(_DSS, 1)
+		  {
+		  }
 		*/
 		acpigen_write_method("_DSS", 1);
-		acpigen_emit_namestring("^^XDSS");
-		acpigen_write_byte(i);
-		acpigen_emit_byte(0x68); /* Arg0Op.  */
 		acpigen_pop_len();
 
 		acpigen_pop_len();