gma config_helpers: Add dot-clock helper functions
Highest_Dotclock() returns the highest dot clock in a set of
pipe configurations.
Limit_Dotclocks() reduces any dot clock to the given maximum
if it exceeds the latter. To prove that Limit_Dotclocks() only
changes timing, we introduce Stable_FB().
Change-Id: Iaa25e774d38c7af12150523739d902cf8e758674
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/35529
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/hw-gfx-gma-config_helpers.ads b/common/hw-gfx-gma-config_helpers.ads
index 7bbf423..f02b6e5 100644
--- a/common/hw-gfx-gma-config_helpers.ads
+++ b/common/hw-gfx-gma-config_helpers.ads
@@ -60,4 +60,25 @@
with
Post => (if Validate_Config'Result then Valid_FB (FB, Mode));
+ -- For still active pipes, ensure only timings
+ -- changed that don't affect FB validity.
+ function Stable_FB (Old_C, New_C : Pipe_Configs) return Boolean is
+ (for all P in Pipe_Index =>
+ New_C (P).Port = Disabled or
+ (New_C (P).Port = Old_C (P).Port and
+ New_C (P).Framebuffer = Old_C (P).Framebuffer and
+ New_C (P).Cursor = Old_C (P).Cursor and
+ New_C (P).Mode.H_Visible = Old_C (P).Mode.H_Visible and
+ New_C (P).Mode.V_Visible = Old_C (P).Mode.V_Visible));
+
+ ----------------------------------------------------------------------------
+
+ function Highest_Dotclock (Configs : Pipe_Configs) return Frequency_Type;
+
+ procedure Limit_Dotclocks
+ (Configs : in out Pipe_Configs;
+ Max : in Frequency_Type)
+ with
+ Post => Stable_FB (Configs'Old, Configs);
+
end HW.GFX.GMA.Config_Helpers;