[PATCH 21/22] drm/amd/display: Correct prefetch calculation

[Zaeem Mohamed]

From: TungYu Lu <tungyu.lu at amd.com>

[Why]
The minimum value of the dst_y_prefetch_equ was not correct
in prefetch calculation whice causes OPTC underflow.

[How]
Add the min operation of dst_y_prefetch_equ in prefetch calculation
for legacy DML.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
Signed-off-by: TungYu Lu <tungyu.lu at amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed at amd.com>
---
 drivers/gpu/drm/amd/display/dc/dml/dcn30/display_mode_vba_30.c   | 1 +
 drivers/gpu/drm/amd/display/dc/dml/dcn31/display_mode_vba_31.c   | 1 +
 drivers/gpu/drm/amd/display/dc/dml/dcn314/display_mode_vba_314.c | 1 +
 3 files changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn30/display_mode_vba_30.c b/drivers/gpu/drm/amd/display/dc/dml/dcn30/display_mode_vba_30.c
index f1fe49401bc0..8d24763938ea 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/dcn30/display_mode_vba_30.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/dcn30/display_mode_vba_30.c
@@ -1002,6 +1002,7 @@ static bool CalculatePrefetchSchedule(
 
 	dst_y_prefetch_equ = VStartup - (Tsetup + dml_max(TWait + TCalc, *Tdmdl)) / LineTime
 			- (*DSTYAfterScaler + *DSTXAfterScaler / myPipe->HTotal);
+	dst_y_prefetch_equ = dml_min(dst_y_prefetch_equ, 63.75); // limit to the reg limit of U6.2 for DST_Y_PREFETCH
 
 	Lsw_oto = dml_max(PrefetchSourceLinesY, PrefetchSourceLinesC);
 	Tsw_oto = Lsw_oto * LineTime;
diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn31/display_mode_vba_31.c b/drivers/gpu/drm/amd/display/dc/dml/dcn31/display_mode_vba_31.c
index f567a9023682..ed59c77bc6f6 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/dcn31/display_mode_vba_31.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/dcn31/display_mode_vba_31.c
@@ -1105,6 +1105,7 @@ static bool CalculatePrefetchSchedule(
 	Tr0_oto_lines = dml_ceil(4.0 * Tr0_oto / LineTime, 1) / 4.0;
 	dst_y_prefetch_oto = Tvm_oto_lines + 2 * Tr0_oto_lines + Lsw_oto;
 	dst_y_prefetch_equ =  VStartup - (*TSetup + dml_max(TWait + TCalc, *Tdmdl)) / LineTime - (*DSTYAfterScaler + *DSTXAfterScaler / myPipe->HTotal);
+	dst_y_prefetch_equ = dml_min(dst_y_prefetch_equ, 63.75); // limit to the reg limit of U6.2 for DST_Y_PREFETCH
 	dst_y_prefetch_equ = dml_floor(4.0 * (dst_y_prefetch_equ + 0.125), 1) / 4.0;
 	Tpre_rounded = dst_y_prefetch_equ * LineTime;
 
diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn314/display_mode_vba_314.c b/drivers/gpu/drm/amd/display/dc/dml/dcn314/display_mode_vba_314.c
index 5865e8fa2d8e..9f3938a50240 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/dcn314/display_mode_vba_314.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/dcn314/display_mode_vba_314.c
@@ -1123,6 +1123,7 @@ static bool CalculatePrefetchSchedule(
 	Tr0_oto_lines = dml_ceil(4.0 * Tr0_oto / LineTime, 1) / 4.0;
 	dst_y_prefetch_oto = Tvm_oto_lines + 2 * Tr0_oto_lines + Lsw_oto;
 	dst_y_prefetch_equ =  VStartup - (*TSetup + dml_max(TWait + TCalc, *Tdmdl)) / LineTime - (*DSTYAfterScaler + *DSTXAfterScaler / myPipe->HTotal);
+	dst_y_prefetch_equ = dml_min(dst_y_prefetch_equ, 63.75); // limit to the reg limit of U6.2 for DST_Y_PREFETCH
 	dst_y_prefetch_equ = dml_floor(4.0 * (dst_y_prefetch_equ + 0.125), 1) / 4.0;
 	Tpre_rounded = dst_y_prefetch_equ * LineTime;
 
-- 
2.34.1