drm/amd/display: Lower DPP DTO only when safe

[Why]
A corner case currently exists where DPP DTO is lowered before
pipes are updated to a higher viewport. This causes underflow
as the DPPCLK is too low for the current viewport.

[How]
Only lower DPP DTO when it is safe to lower, or if
the newer clocks are higher than the current ones.
Signed-off-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn20/dcn20_clk_mgr.c

@@ -101,13 +101,13 @@ uint32_t dentist_get_did_from_divider(int divider)
 }
 
 void dcn20_update_clocks_update_dpp_dto(struct clk_mgr_internal *clk_mgr,
-		struct dc_state *context)
+		struct dc_state *context, bool safe_to_lower)
 {
 	int i;
 
 	clk_mgr->dccg->ref_dppclk = clk_mgr->base.clks.dppclk_khz;
 	for (i = 0; i < clk_mgr->base.ctx->dc->res_pool->pipe_count; i++) {
-		int dpp_inst, dppclk_khz;
+		int dpp_inst, dppclk_khz, prev_dppclk_khz;
 
 		/* Loop index will match dpp->inst if resource exists,
 		 * and we want to avoid dependency on dpp object
@@ -115,9 +115,13 @@ void dcn20_update_clocks_update_dpp_dto(struct clk_mgr_internal *clk_mgr,
 		dpp_inst = i;
 		dppclk_khz = context->res_ctx.pipe_ctx[i].plane_res.bw.dppclk_khz;
 
+		prev_dppclk_khz = clk_mgr->base.ctx->dc->current_state->res_ctx.pipe_ctx[i].plane_res.bw.dppclk_khz;
+
+		if (safe_to_lower || prev_dppclk_khz < dppclk_khz) {
 			clk_mgr->dccg->funcs->update_dpp_dto(
 							clk_mgr->dccg, dpp_inst, dppclk_khz);
 		}
+	}
 }
 
 void dcn20_update_clocks_update_dentist(struct clk_mgr_internal *clk_mgr)
@@ -244,7 +248,7 @@ void dcn2_update_clocks(struct clk_mgr *clk_mgr_base,
 	if (dc->config.forced_clocks == false || (force_reset && safe_to_lower)) {
 		if (dpp_clock_lowered) {
 			// if clock is being lowered, increase DTO before lowering refclk
-			dcn20_update_clocks_update_dpp_dto(clk_mgr, context);
+			dcn20_update_clocks_update_dpp_dto(clk_mgr, context, safe_to_lower);
 			dcn20_update_clocks_update_dentist(clk_mgr);
 		} else {
 			// if clock is being raised, increase refclk before lowering DTO
@@ -252,7 +256,7 @@ void dcn2_update_clocks(struct clk_mgr *clk_mgr_base,
 				dcn20_update_clocks_update_dentist(clk_mgr);
 			// always update dtos unless clock is lowered and not safe to lower
 			if (new_clocks->dppclk_khz >= dc->current_state->bw_ctx.bw.dcn.clk.dppclk_khz)
-				dcn20_update_clocks_update_dpp_dto(clk_mgr, context);
+				dcn20_update_clocks_update_dpp_dto(clk_mgr, context, safe_to_lower);
 		}
 	}
 

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn20/dcn20_clk_mgr.h

@@ -34,7 +34,7 @@ void dcn2_update_clocks_fpga(struct clk_mgr *clk_mgr,
 			struct dc_state *context,
 			bool safe_to_lower);
 void dcn20_update_clocks_update_dpp_dto(struct clk_mgr_internal *clk_mgr,
-		struct dc_state *context);
+		struct dc_state *context, bool safe_to_lower);
 
 void dcn2_init_clocks(struct clk_mgr *clk_mgr);
 

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c

@@ -164,16 +164,16 @@ void rn_update_clocks(struct clk_mgr *clk_mgr_base,
 	}
 
 	if (dpp_clock_lowered) {
-		// if clock is being lowered, increase DTO before lowering refclk
-		dcn20_update_clocks_update_dpp_dto(clk_mgr, context);
+		// increase per DPP DTO before lowering global dppclk
+		dcn20_update_clocks_update_dpp_dto(clk_mgr, context, safe_to_lower);
 		rn_vbios_smu_set_dppclk(clk_mgr, clk_mgr_base->clks.dppclk_khz);
 	} else {
-		// if clock is being raised, increase refclk before lowering DTO
+		// increase global DPPCLK before lowering per DPP DTO
 		if (update_dppclk || update_dispclk)
 			rn_vbios_smu_set_dppclk(clk_mgr, clk_mgr_base->clks.dppclk_khz);
 		// always update dtos unless clock is lowered and not safe to lower
 		if (new_clocks->dppclk_khz >= dc->current_state->bw_ctx.bw.dcn.clk.dppclk_khz)
-			dcn20_update_clocks_update_dpp_dto(clk_mgr, context);
+			dcn20_update_clocks_update_dpp_dto(clk_mgr, context, safe_to_lower);
 	}
 
 	if (update_dispclk &&