drm/amd/display: handle max_downscale_src_width fail check

[ Upstream commit 02a940d ]

[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@amd.com>
Signed-off-by: Yihan Zhu <Yihan.Zhu@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit ec6f764ab7009857f36c9082f087c8938186121c)

Author: Yihan Zhu

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);