[XS] Change in coreboot[master]: mb/google/skyrim/: Set system_configuration to 3 to avoid SMU call

[Martin L Roth (Code Review)]

Martin L Roth has submitted this change. ( https://review.coreboot.org/c/coreboot/+/76091?usp=email )

Change subject: mb/google/skyrim/: Set system_configuration to 3 to avoid SMU call
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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 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76091
Reviewed-by: Marshall Dawson 
Reviewed-by: Eric Lai 
Reviewed-by: Martin Roth 
Tested-by: build bot (Jenkins) 
Reviewed-by: Tim Van Patten 
---
M src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
1 file changed, 4 insertions(+), 2 deletions(-)

Approvals:
  Tim Van Patten: Looks good to me, but someone else must approve
  build bot (Jenkins): Verified
  Martin Roth: Looks good to me, approved
  Marshall Dawson: Looks good to me, approved
  Eric Lai: Looks good to me, approved

diff --git a/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb b/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
index b605e1c..77f23be 100644
--- a/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
+++ b/src/mainboard/google/skyrim/variants/baseboard/devicetree.cb
@@ -262,8 +262,10 @@
    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"