Nico Huber submitted this change.

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gma g45 config: Limit HDMI rate to 165MHz

Tests with a 3440x1440 pixel display have shown that the dot clock
was chosen much too high (we got either 720x1440 at half the rate
or a completely garbled picture). Turns out, Linux' i915 limits the
clock to the original DVI's 165MHz for 4th gen and earlier, so we'll
do that too. This resulted in a stable picture with 3440x1440 @ 31Hz
(the display even synchronized better on this than the configuration
chosen by i915).

Change-Id: I30cb67feedd776148457101d1ca3e3b8538e672f
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/35779
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
---
M common/hw-gfx-gma-config.ads.template
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/common/hw-gfx-gma-config.ads.template b/common/hw-gfx-gma-config.ads.template
index d5bd2ba..e4e557a 100644
--- a/common/hw-gfx-gma-config.ads.template
+++ b/common/hw-gfx-gma-config.ads.template
@@ -322,7 +322,10 @@
 
    -- FIXME: Unknown for Broxton, Linux' i915 contains a fixme too :-D
    HDMI_Max_Clock_24bpp : constant Frequency_Type :=
-     (if Haswell_On then 300_000_000 else 225_000_000);
+     (case Gen is
+         when Generation'First .. G45     => 165_000_000,
+         when Ironlake                    => 225_000_000,
+         when Haswell .. Generation'Last  => 300_000_000);
 
    ----------------------------------------------------------------------------
 

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