linux-kernel - [PATCH AUTOSEL 6.6 155/294] drm/amd/display: handle max_downscale_src

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Message-Id: <20250505225634.2688578-155-sashal@kernel.org>
Date: Mon,  5 May 2025 18:54:15 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Yihan Zhu <Yihan.Zhu@....com>,
	Samson Tam <samson.tam@....com>,
	Zaeem Mohamed <zaeem.mohamed@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Sasha Levin <sashal@...nel.org>,
	harry.wentland@....com,
	sunpeng.li@....com,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.6 155/294] drm/amd/display: handle max_downscale_src_width fail check

From: Yihan Zhu <Yihan.Zhu@....com>

[ Upstream commit 02a940da2ccc0cc0299811379580852b405a0ea2 ]

[WHY]
If max_downscale_src_width check fails, we exit early from TAP calculation and left a NULL
value to the scaling data structure to cause the zero divide in the DML validation.

[HOW]
Call set default TAP calculation before early exit in get_optimal_number_of_taps due to
max downscale limit exceed.

Reviewed-by: Samson Tam <samson.tam@....com>
Signed-off-by: Yihan Zhu <Yihan.Zhu@....com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
index 50dc834046446..4ce45f1bdac0f 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
@@ -392,11 +392,6 @@ bool dpp3_get_optimal_number_of_taps(
 	int min_taps_y, min_taps_c;
 	enum lb_memory_config lb_config;
 
-	if (scl_data->viewport.width > scl_data->h_active &&
-		dpp->ctx->dc->debug.max_downscale_src_width != 0 &&
-		scl_data->viewport.width > dpp->ctx->dc->debug.max_downscale_src_width)
-		return false;
-
 	/*
 	 * Set default taps if none are provided
 	 * From programming guide: taps = min{ ceil(2*H_RATIO,1), 8} for downscaling
@@ -434,6 +429,12 @@ bool dpp3_get_optimal_number_of_taps(
 	else
 		scl_data->taps.h_taps_c = in_taps->h_taps_c;
 
+	// Avoid null data in the scl data with this early return, proceed non-adaptive calcualtion first
+	if (scl_data->viewport.width > scl_data->h_active &&
+		dpp->ctx->dc->debug.max_downscale_src_width != 0 &&
+		scl_data->viewport.width > dpp->ctx->dc->debug.max_downscale_src_width)
+		return false;
+
 	/*Ensure we can support the requested number of vtaps*/
 	min_taps_y = dc_fixpt_ceil(scl_data->ratios.vert);
 	min_taps_c = dc_fixpt_ceil(scl_data->ratios.vert_c);
-- 
2.39.5