linux-kernel - [PATCH AUTOSEL 6.5 15/36] drm/amd/display: Fix underflow issue on 175hz timing

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Message-Id: <20230908192848.3462476-15-sashal@kernel.org>
Date:   Fri,  8 Sep 2023 15:28:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Leo Ma <hanghong.ma@....com>,
        Dillon Varone <dillon.varone@....com>,
        Alex Hung <alex.hung@....com>,
        Daniel Wheeler <daniel.wheeler@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>, harry.wentland@....com,
        sunpeng.li@....com, Rodrigo.Siqueira@....com,
        christian.koenig@....com, Xinhui.Pan@....com, airlied@...il.com,
        daniel@...ll.ch, Alvin.Lee2@....com, Jun.Lei@....com,
        nathan@...nel.org, george.shen@....com, samson.tam@....com,
        chris.park@....com, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.5 15/36] drm/amd/display: Fix underflow issue on 175hz timing

From: Leo Ma <hanghong.ma@....com>

[ Upstream commit 735688eb905db529efea0c78466fccc1461c3fde ]

[Why]
Screen underflows happen on 175hz timing for 3 plane overlay case.

[How]
Based on dst y prefetch value clamp to equ or oto for bandwidth
calculation.

Reviewed-by: Dillon Varone <dillon.varone@....com>
Acked-by: Alex Hung <alex.hung@....com>
Signed-off-by: Leo Ma <hanghong.ma@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../amd/display/dc/dml/dcn32/display_mode_vba_util_32.c    | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c b/drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
index a50e7f4dce421..f74e5fc8218f5 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/dcn32/display_mode_vba_util_32.c
@@ -3459,6 +3459,7 @@ bool dml32_CalculatePrefetchSchedule(
 	double TimeForFetchingMetaPTE = 0;
 	double TimeForFetchingRowInVBlank = 0;
 	double LinesToRequestPrefetchPixelData = 0;
+	double LinesForPrefetchBandwidth = 0;
 	unsigned int HostVMDynamicLevelsTrips;
 	double  trip_to_mem;
 	double  Tvm_trips;
@@ -3888,11 +3889,15 @@ bool dml32_CalculatePrefetchSchedule(
 			TimeForFetchingMetaPTE = Tvm_oto;
 			TimeForFetchingRowInVBlank = Tr0_oto;
 			*PrefetchBandwidth = prefetch_bw_oto;
+			/* 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;
 		}
 
 		*DestinationLinesToRequestVMInVBlank = dml_ceil(4.0 * TimeForFetchingMetaPTE / LineTime, 1.0) / 4.0;
@@ -3900,7 +3905,7 @@ bool dml32_CalculatePrefetchSchedule(
 		*DestinationLinesToRequestRowInVBlank =
 				dml_ceil(4.0 * TimeForFetchingRowInVBlank / LineTime, 1.0) / 4.0;
 
-		LinesToRequestPrefetchPixelData = *DestinationLinesForPrefetch -
+		LinesToRequestPrefetchPixelData = LinesForPrefetchBandwidth -
 				*DestinationLinesToRequestVMInVBlank - 2 * *DestinationLinesToRequestRowInVBlank;
 
 #ifdef __DML_VBA_DEBUG__
-- 
2.40.1