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gma: Limit HDMI pixel rate

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Given that current Intel chips only support 4K@30Hz over HDMI, it's
actually no surprise that older chips had even lower limits. For a
24bpp mode, it's 225MHz for Nehalem, Sandy and Ivy Bridge and 300MHz
for everything newer.

To keep the code most simple we keep the display's native resolution
and just limit the clock if we encouter an unsupported mode.

TEST=Booted T420 with a DELL U3415W attached over DP-to-HDMI and
     DVI-to-HDMI adapters. The display came up with 3440x1440@42Hz
     (instead of a garbled picture at 1720x1440@60Hz).

Change-Id: I5386386c648db267a49ed1f62750d2a5fdb2d934
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17499
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
This commit is contained in:
Nico Huber
2016-11-19 03:00:43 +01:00
parent fbb4220155
commit 74ec962821
2 changed files with 22 additions and 0 deletions
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5
common/hw-gfx-gma-config.ads.template
View File

@@ -248,4 +248,9 @@ is
Secondary => 4096,
Tertiary => 4096));
----------------------------------------------------------------------------
HDMI_Max_Clock_24bpp : constant Frequency_Type :=
(if CPU >= Haswell then 300_000_000 else 225_000_000);
end HW.GFX.GMA.Config;

17
common/hw-gfx-gma.adb
View File

@@ -237,6 +237,23 @@ is
if Port_Cfg.Mode.BPC = Auto_BPC then
Port_Cfg.Mode.BPC := Connector_Info.Default_BPC (Port_Cfg);
end if;
if Port_Cfg.Display = HDMI then
declare
pragma Assert (Config.HDMI_Max_Clock_24bpp * 8
/ Port_Cfg.Mode.BPC >= Frequency_Type'First);
Max_Dotclock : constant Frequency_Type :=
Config.HDMI_Max_Clock_24bpp * 8 / Port_Cfg.Mode.BPC;
begin
if Port_Cfg.Mode.Dotclock > Max_Dotclock then
pragma Debug (Debug.Put ("Dotclock "));
pragma Debug (Debug.Put_Int64 (Port_Cfg.Mode.Dotclock));
pragma Debug (Debug.Put (" too high, limiting to "));
pragma Debug (Debug.Put_Int64 (Max_Dotclock));
pragma Debug (Debug.Put_Line ("."));
Port_Cfg.Mode.Dotclock := Max_Dotclock;
end if;
end;
end if;
end;
else
Port_Cfg := Port_Config'