drm/amd/display: For prefetch mode > 0, extend prefetch if possible

From Alvin Lee
6750d1de747f4d2db0046a25b069e15341f6a9ba in linux-6.6.y/6.6.16
dd4e4bb28843393065eed279e869fac248d03f0f in mainline linux

3 files changed, 31 insertions, 6 deletions

diff --git a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c
index cbdfb762c10..6c84b0fa40f 100644
--- a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c
+++ b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_32.c
@@ -813,6 +813,8 @@ static void DISPCLKDPPCLKDCFCLKDeepSleepPrefetchParametersWatermarksAndPerforman
 					(v->DRAMSpeedPerState[mode_lib->vba.VoltageLevel] <= MEM_STROBE_FREQ_MHZ ||
 						v->DCFCLKPerState[mode_lib->vba.VoltageLevel] <= DCFCLK_FREQ_EXTRA_PREFETCH_REQ_MHZ) ?
 							mode_lib->vba.ip.min_prefetch_in_strobe_us : 0,
+					mode_lib->vba.PrefetchModePerState[mode_lib->vba.VoltageLevel][mode_lib->vba.maxMpcComb] > 0 || mode_lib->vba.DRAMClockChangeRequirementFinal == false,
+
 					/* Output */
 					&v->DSTXAfterScaler[k],
 					&v->DSTYAfterScaler[k],
@@ -3317,6 +3319,7 @@ void dml32_ModeSupportAndSystemConfigurationFull(struct display_mode_lib *mode_l
 							v->SwathHeightCThisState[k], v->TWait,
 							(v->DRAMSpeedPerState[i] <= MEM_STROBE_FREQ_MHZ || v->DCFCLKState[i][j] <= DCFCLK_FREQ_EXTRA_PREFETCH_REQ_MHZ) ?
 									mode_lib->vba.ip.min_prefetch_in_strobe_us : 0,
+							mode_lib->vba.PrefetchModePerState[i][j] > 0 || mode_lib->vba.DRAMClockChangeRequirementFinal == false,
 
 							/* Output */
 							&v->dummy_vars.dml32_ModeSupportAndSystemConfigurationFull.DSTXAfterScaler[k],
diff --git a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
index ecea008f19d..208b89d13d3 100644
--- a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
+++ b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
@@ -3423,6 +3423,7 @@ bool dml32_CalculatePrefetchSchedule(
 		unsigned int SwathHeightC,
 		double TWait,
 		double TPreReq,
+		bool ExtendPrefetchIfPossible,
 		/* Output */
 		double   *DSTXAfterScaler,
 		double   *DSTYAfterScaler,
@@ -3892,12 +3893,32 @@ bool dml32_CalculatePrefetchSchedule(
 			/* Clamp to oto for bandwidth calculation */
 			LinesForPrefetchBandwidth = dst_y_prefetch_oto;
 		} else {
-			*DestinationLinesForPrefetch = dst_y_prefetch_equ;
-			TimeForFetchingMetaPTE = Tvm_equ;
-			TimeForFetchingRowInVBlank = Tr0_equ;
-			*PrefetchBandwidth = prefetch_bw_equ;
-			/* Clamp to equ for bandwidth calculation */
-			LinesForPrefetchBandwidth = dst_y_prefetch_equ;
+			/* For mode programming we want to extend the prefetch as much as possible
+			 * (up to oto, or as long as we can for equ) if we're not already applying
+			 * the 60us prefetch requirement. This is to avoid intermittent underflow
+			 * issues during prefetch.
+			 *
+			 * The prefetch extension is applied under the following scenarios:
+			 * 1. We're in prefetch mode > 0 (i.e. we don't support MCLK switch in blank)
+			 * 2. We're using subvp or drr methods of p-state switch, in which case we
+			 *    we don't care if prefetch takes up more of the blanking time
+			 *
+			 * Mode programming typically chooses the smallest prefetch time possible
+			 * (i.e. highest bandwidth during prefetch) presumably to create margin between
+			 * p-states / c-states that happen in vblank and prefetch. Therefore we only
+			 * apply this prefetch extension when p-state in vblank is not required (UCLK
+			 * p-states take up the most vblank time).
+			 */
+			if (ExtendPrefetchIfPossible && TPreReq == 0 && VStartup < MaxVStartup) {
+				MyError = true;
+			} else {
+				*DestinationLinesForPrefetch = dst_y_prefetch_equ;
+				TimeForFetchingMetaPTE = Tvm_equ;
+				TimeForFetchingRowInVBlank = Tr0_equ;
+				*PrefetchBandwidth = prefetch_bw_equ;
+				/* Clamp to equ for bandwidth calculation */
+				LinesForPrefetchBandwidth = dst_y_prefetch_equ;
+			}
 		}
 
 		*DestinationLinesToRequestVMInVBlank = dml_ceil(4.0 * TimeForFetchingMetaPTE / LineTime, 1.0) / 4.0;
diff --git a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.h b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.h
index 592d174df6c..5d34735df83 100644
--- a/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.h
+++ b/sys/dev/pci/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.h
@@ -747,6 +747,7 @@ bool dml32_CalculatePrefetchSchedule(
 		unsigned int SwathHeightC,
 		double TWait,
 		double TPreReq,
+		bool ExtendPrefetchIfPossible,
 		/* Output */
 		double   *DSTXAfterScaler,
 		double   *DSTYAfterScaler,