[XS] Change in coreboot[master]: mb/google/{rex,ovis}: Disable C1-state auto demotion for rex & ovis

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/76827?usp=email )

Change subject: mb/google/{rex,ovis}: Disable C1-state auto demotion for rex & ovis
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mb/google/{rex,ovis}: Disable C1-state auto demotion for rex & ovis

C1-state auto demotion feature allows hardware to determine C1-state
as per platform policy. Since platform sets performance policy to
balanced from hardware, auto demotion can be disabled without
performance impact.

Also, disabling this feature results soc to enter PC2 and lower
state in camera preview case and save platform power.

Note: C1 demotion heuristics used EPB parameter to balance between power
and performance, i.e. low threshold when EPB is low in-order to get C1
demotion faster and vice-versa. ChromeOS operates at default EPB=0x7
(low EPB) in both AC/DC, so in DC mode it gets more C1 demotion hits
than expected (similar to AC mode) and losing power respectively.

BUG=b:286328295
TEST=Code compiles and correct value of c1-state auto demotion is
passed to FSP. Also verified PC residency improvement ~10% in
camera preview case.

Change-Id: I548e0e5340dec537d05718dd2f4652e10fb36ac0
Signed-off-by: Sukumar Ghorai 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76827
Tested-by: build bot (Jenkins) 
Reviewed-by: Subrata Banik 
Reviewed-by: Sumeet R Pawnikar 
Reviewed-by: Sridhar Siricilla 
Reviewed-by: Kapil Porwal 
Reviewed-by: Eric Lai 
---
M src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb
M src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
2 files changed, 6 insertions(+), 0 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Subrata Banik: Looks good to me, approved
  Kapil Porwal: Looks good to me, approved
  Eric Lai: Looks good to me, approved
  Sumeet R Pawnikar: Looks good to me, but someone else must approve
  Sridhar Siricilla: Looks good to me, approved

diff --git a/src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb b/src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb
index 75fef6d..6fc0dc0 100644
--- a/src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb
+++ b/src/mainboard/google/rex/variants/baseboard/ovis/devicetree.cb
@@ -33,6 +33,9 @@
    # S0ix enable
    register "s0ix_enable" = "1"

+	# Disable C1 C-state auto-demotion
+	register "disable_c1_state_auto_demotion" = "1"
+
    # Enable Energy Reporting
    register "pch_pm_energy_report_enable" = "1"

diff --git a/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb b/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
index 57a5288..b21c011 100644
--- a/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
+++ b/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
@@ -33,6 +33,9 @@
    # S0ix enable
    register "s0ix_enable" = "1"

+	# Disable C1 C-state auto-demotion
+	register "disable_c1_state_auto_demotion" = "1"
+
    # Enable Energy Reporting
    register "pch_pm_energy_report_enable" = "1"