drm/amd/display: Increase minimum clock for TMDS 420 with pipe splitting

[Why]
-Pipe splitting allows for clocks to be reduced, but when using TMDS 420,
reduced clocks lead to missed clocks cycles on clock resyncing

[How]
-Impose a minimum clock when using TMDS 420

Reviewed-by: Chris Park <chris.park@amd.com>
Signed-off-by: Relja Vojvodic <rvojvodi@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Relja Vojvodic

drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c

@@ -1238,18 +1238,27 @@ static void CalculateDETBufferSize(
 
 static double CalculateRequiredDispclk(
 	enum dml2_odm_mode ODMMode,
-	double PixelClock)
+	double PixelClock,
+	bool isTMDS420)
 {
+	double DispClk;
 
 	if (ODMMode == dml2_odm_mode_combine_4to1) {
-		return PixelClock / 4.0;
+		DispClk = PixelClock / 4.0;
 	} else if (ODMMode == dml2_odm_mode_combine_3to1) {
-		return PixelClock / 3.0;
+		DispClk = PixelClock / 3.0;
 	} else if (ODMMode == dml2_odm_mode_combine_2to1) {
-		return PixelClock / 2.0;
+		DispClk = PixelClock / 2.0;
 	} else {
-		return PixelClock;
+		DispClk = PixelClock;
+	}
+
+	if (isTMDS420) {
+		double TMDS420MinPixClock = PixelClock / 2.0;
+		DispClk = math_max2(DispClk, TMDS420MinPixClock);
 	}
+
+	return DispClk;
 }
 
 static double TruncToValidBPP(
@@ -4122,11 +4131,12 @@ static noinline_for_stack void CalculateODMMode(
 	bool success;
 	bool UseDSC = DSCEnable && (NumberOfDSCSlices > 0);
 	enum dml2_odm_mode DecidedODMMode;
+	bool isTMDS420 = (OutFormat == dml2_420 && Output == dml2_hdmi);
 
-	SurfaceRequiredDISPCLKWithoutODMCombine = CalculateRequiredDispclk(dml2_odm_mode_bypass, PixelClock);
-	SurfaceRequiredDISPCLKWithODMCombineTwoToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_2to1, PixelClock);
-	SurfaceRequiredDISPCLKWithODMCombineThreeToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_3to1, PixelClock);
-	SurfaceRequiredDISPCLKWithODMCombineFourToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_4to1, PixelClock);
+	SurfaceRequiredDISPCLKWithoutODMCombine = CalculateRequiredDispclk(dml2_odm_mode_bypass, PixelClock, isTMDS420);
+	SurfaceRequiredDISPCLKWithODMCombineTwoToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_2to1, PixelClock, isTMDS420);
+	SurfaceRequiredDISPCLKWithODMCombineThreeToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_3to1, PixelClock, isTMDS420);
+	SurfaceRequiredDISPCLKWithODMCombineFourToOne = CalculateRequiredDispclk(dml2_odm_mode_combine_4to1, PixelClock, isTMDS420);
 #ifdef __DML_VBA_DEBUG__
 	DML_LOG_VERBOSE("DML::%s: ODMUse = %d\n", __func__, ODMUse);
 	DML_LOG_VERBOSE("DML::%s: Output = %d\n", __func__, Output);