drm/amd/display: Set max for prefetch lines on dcn32

[WHY?]
Max number of lines that can be used for prefetch due to type constraints is
63.75.

[HOW?]
Enforce maximum prefetch lines as 63.75.
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.h

@@ -46,6 +46,8 @@
 // Prefetch schedule max vratio
 #define __DML_MAX_VRATIO_PRE__ 4.0
 
+#define __DML_VBA_MAX_DST_Y_PRE__    63.75
+
 #define BPP_INVALID 0
 #define BPP_BLENDED_PIPE 0xffffffff
 

drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c

@@ -3475,7 +3475,6 @@ bool dml32_CalculatePrefetchSchedule(
 	double  min_Lsw;
 	double  Tsw_est1 = 0;
 	double  Tsw_est3 = 0;
-	double  TPreMargin = 0;
 
 	if (v->GPUVMEnable == true && v->HostVMEnable == true)
 		HostVMDynamicLevelsTrips = v->HostVMMaxNonCachedPageTableLevels;
@@ -3669,6 +3668,7 @@ bool dml32_CalculatePrefetchSchedule(
 	dst_y_prefetch_equ = VStartup - (*TSetup + dml_max(TWait + TCalc, *Tdmdl)) / LineTime -
 			(*DSTYAfterScaler + (double) *DSTXAfterScaler / (double) myPipe->HTotal);
 
+	dst_y_prefetch_equ = dml_min(dst_y_prefetch_equ, __DML_VBA_MAX_DST_Y_PRE__);
 #ifdef __DML_VBA_DEBUG__
 	dml_print("DML::%s: HTotal = %d\n", __func__, myPipe->HTotal);
 	dml_print("DML::%s: min_Lsw = %f\n", __func__, min_Lsw);
@@ -3701,8 +3701,6 @@ bool dml32_CalculatePrefetchSchedule(
 
 	dst_y_prefetch_equ = dml_floor(4.0 * (dst_y_prefetch_equ + 0.125), 1) / 4.0;
 	Tpre_rounded = dst_y_prefetch_equ * LineTime;
-
-	TPreMargin = Tpre_rounded - TPreReq;
 #ifdef __DML_VBA_DEBUG__
 	dml_print("DML::%s: dst_y_prefetch_equ: %f (after round)\n", __func__, dst_y_prefetch_equ);
 	dml_print("DML::%s: LineTime: %f\n", __func__, LineTime);
@@ -3730,7 +3728,8 @@ bool dml32_CalculatePrefetchSchedule(
 	*VRatioPrefetchY = 0;
 	*VRatioPrefetchC = 0;
 	*RequiredPrefetchPixDataBWLuma = 0;
-	if (dst_y_prefetch_equ > 1 && TPreMargin > 0.0) {
+	if (dst_y_prefetch_equ > 1 &&
+			(Tpre_rounded >= TPreReq || dst_y_prefetch_equ == __DML_VBA_MAX_DST_Y_PRE__)) {
 		double PrefetchBandwidth1;
 		double PrefetchBandwidth2;
 		double PrefetchBandwidth3;