mb/google/skyrim/: Set system_configuration to 3 to avoid SMU call

Update system_configuration to 3 for 15W. Specification "FT6
Infrastructure Roadmap #57316" incorrectly lists system config index
of 4 for 15W. Setting to 4 will cause an additional call to the SMU
that is not needed and will add boot delay. Both SMU and FSP interpret
configs > 3 as 3.

BUG=b:267294958
TEST=Confirm extra message "Service Request 0x5F" not in log.

Change-Id: I1f3e305c48801b4e499de56d06c0dcd3eeacc626
Signed-off-by: Jason Glenesk <jason.glenesk@amd.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76091
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Van Patten <timvp@google.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb b/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
index b605e1cd43..77f23be3f6 100644
--- a/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
+++ b/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
@@ -262,8 +262,10 @@ chip soc/amd/mendocino
 	end
 
 	# DPTC: Refer the spec "FT6 Infrastructure Roadmap"#57316
-	# Set system_configuration to 4 for 15W
-	register "system_configuration" = "4"
+	# Set system_configuration to 3 for 15W. Spec lists 4 for 15W,
+	# however, setting to 3 will avoid an additional communication
+	# with the SMU and save boot time.
+	register "system_configuration" = "3"
 	# Normal
 	register "slow_ppt_limit_mW"                     = "25000"
 	register "fast_ppt_limit_mW"                     = "30000"