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From b42ca30081b25cbabfb2659adca9d935ef3a8399 Mon Sep 17 00:00:00 2001
From: Nicholas Chin <nic.c3.14@gmail.com>
Date: Mon, 20 May 2024 10:24:16 -0600
Subject: [PATCH 3/3] mb/dell/e6400: Use 100 MHz reference clock for display
The E6400 uses a 100 MHz reference clock for spread spectrum support on
LVDS, whereas libgfxinit previously assumed a 96 MHz input clock. For
the more common 1280 x 800 display panels, the numerical error was not
large enough to cause noticable issues, but the actual pixel clock
frequency derived from a 100 MHz reference using PLL configs calculated
assuming a 96 MHz reference was not close enough for 1440 x 900 panels,
which require a much higher pixel clock. This resulted in a garbled
display in the pre-OS graphics environment provided by libgfxinit.
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
---
src/mainboard/dell/e6400/Kconfig | 3 +++
src/northbridge/intel/gm45/Kconfig | 4 ++++
2 files changed, 7 insertions(+)
diff --git a/src/mainboard/dell/e6400/Kconfig b/src/mainboard/dell/e6400/Kconfig
index 417d95fd5d..6fe1b1c456 100644
--- a/src/mainboard/dell/e6400/Kconfig
+++ b/src/mainboard/dell/e6400/Kconfig
@@ -19,6 +19,9 @@ config BOARD_SPECIFIC_OPTIONS
select INTEL_GMA_HAVE_VBT
select EC_DELL_MEC5035
+config INTEL_GMA_DPLL_REF_FREQ
+ default 100000000
+
config MAINBOARD_DIR
default "dell/e6400"
diff --git a/src/northbridge/intel/gm45/Kconfig b/src/northbridge/intel/gm45/Kconfig
index 8059e7ee80..5df5a93296 100644
--- a/src/northbridge/intel/gm45/Kconfig
+++ b/src/northbridge/intel/gm45/Kconfig
@@ -14,6 +14,10 @@ config NORTHBRIDGE_INTEL_GM45
if NORTHBRIDGE_INTEL_GM45
+config INTEL_GMA_DPLL_REF_FREQ
+ int
+ default 96000000
+
config VBOOT
select VBOOT_STARTS_IN_BOOTBLOCK
--
2.39.2
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