drm/amd/display: Revert vblank change that causes null pointer crash

Revert commit 1a4bcdbe ("drm/amd/display: Fix possible underflow for displays with large vblank")
Because it cause some regression

Fixes: 1a4bcdbe ("drm/amd/display: Fix possible underflow for displays with large vblank")
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@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/dml/dcn314/dcn314_fpu.c

@@ -33,7 +33,7 @@
 #include "dml/display_mode_vba.h"
 
 struct _vcs_dpi_ip_params_st dcn3_14_ip = {
-	.VBlankNomDefaultUS = 800,
+	.VBlankNomDefaultUS = 668,
 	.gpuvm_enable = 1,
 	.gpuvm_max_page_table_levels = 1,
 	.hostvm_enable = 1,
@@ -286,7 +286,7 @@ int dcn314_populate_dml_pipes_from_context_fpu(struct dc *dc, struct dc_state *c
 	struct resource_context *res_ctx = &context->res_ctx;
 	struct pipe_ctx *pipe;
 	bool upscaled = false;
-	const unsigned int max_allowed_vblank_nom = 1023;
+	bool isFreesyncVideo = false;
 
 	dc_assert_fp_enabled();
 
@@ -300,11 +300,16 @@ int dcn314_populate_dml_pipes_from_context_fpu(struct dc *dc, struct dc_state *c
 		pipe = &res_ctx->pipe_ctx[i];
 		timing = &pipe->stream->timing;
 
-		pipes[pipe_cnt].pipe.dest.vtotal = pipe->stream->adjust.v_total_min;
-		pipes[pipe_cnt].pipe.dest.vblank_nom = timing->v_total - pipes[pipe_cnt].pipe.dest.vactive;
-		pipes[pipe_cnt].pipe.dest.vblank_nom = min(pipes[pipe_cnt].pipe.dest.vblank_nom, dcn3_14_ip.VBlankNomDefaultUS);
-		pipes[pipe_cnt].pipe.dest.vblank_nom = max(pipes[pipe_cnt].pipe.dest.vblank_nom, timing->v_sync_width);
-		pipes[pipe_cnt].pipe.dest.vblank_nom = min(pipes[pipe_cnt].pipe.dest.vblank_nom, max_allowed_vblank_nom);
+		isFreesyncVideo = pipe->stream->adjust.v_total_max == pipe->stream->adjust.v_total_min;
+		isFreesyncVideo = isFreesyncVideo && pipe->stream->adjust.v_total_min > timing->v_total;
+
+		if (!isFreesyncVideo) {
+			pipes[pipe_cnt].pipe.dest.vblank_nom =
+				dcn3_14_ip.VBlankNomDefaultUS / (timing->h_total / (timing->pix_clk_100hz / 10000.0));
+		} else {
+			pipes[pipe_cnt].pipe.dest.vtotal = pipe->stream->adjust.v_total_min;
+			pipes[pipe_cnt].pipe.dest.vblank_nom = timing->v_total - pipes[pipe_cnt].pipe.dest.vactive;
+		}
 
 		if (pipe->plane_state &&
 				(pipe->plane_state->src_rect.height < pipe->plane_state->dst_rect.height ||