drm/amd/display: fix use_max_lb flag for 420 pixel formats

Right now the flag simply selects memory config 0 when flag is true
however 420 modes benefit more from memory config 3.
Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp_dscl.c

@@ -496,10 +496,13 @@ static enum lb_memory_config dpp1_dscl_find_lb_memory_config(struct dcn10_dpp *d
 	int vtaps_c = scl_data->taps.v_taps_c;
 	int ceil_vratio = dc_fixpt_ceil(scl_data->ratios.vert);
 	int ceil_vratio_c = dc_fixpt_ceil(scl_data->ratios.vert_c);
-	enum lb_memory_config mem_cfg = LB_MEMORY_CONFIG_0;
 
-	if (dpp->base.ctx->dc->debug.use_max_lb)
-		return mem_cfg;
+	if (dpp->base.ctx->dc->debug.use_max_lb) {
+		if (scl_data->format == PIXEL_FORMAT_420BPP8
+				|| scl_data->format == PIXEL_FORMAT_420BPP10)
+			return LB_MEMORY_CONFIG_3;
+		return LB_MEMORY_CONFIG_0;
+	}
 
 	dpp->base.caps->dscl_calc_lb_num_partitions(
 			scl_data, LB_MEMORY_CONFIG_1, &num_part_y, &num_part_c);