drm/amd/display: Maintain consistent mode of operation during encoder assignment

[Why]
While applying a state to hardware, there is a transition period where
the back-end is reset using the old state; then enabled using the new
state.

Generally, the link encoder configuration module queries
stream-to-encoder assignments in either the new or old state based on a
mode variable. During the transition there is a need to query both
states, however toggling this mode variable can lead to incorrect
programming of encoders.

[How]
- Add new function to explicity query stream-to-encoder assignment
in the current state rather than intermittently switch the mode
of operation of the link encoder assignment module.
- Add additional checks for encoder assignment defects.
- Explicitly reset the mode of operation if application of state
to hardware ends prematurely.

Acked-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Jimmy Kizito <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/core/dc.c

···
 
 	result = dc->hwss.apply_ctx_to_hw(dc, context);
 
-	if (result != DC_OK)
+	if (result != DC_OK) {
+		/* Application of dc_state to hardware stopped. */
+		dc->current_state->res_ctx.link_enc_cfg_ctx.mode = LINK_ENC_CFG_STEADY;
 		return result;
+	}
 
 	dc_trigger_sync(dc, context);
 

drivers/gpu/drm/amd/display/dc/core/dc_link_enc_cfg.c

···
 	int j;
 
 	ASSERT(state->stream_count == stream_count);
+	ASSERT(dc->current_state->res_ctx.link_enc_cfg_ctx.mode == LINK_ENC_CFG_STEADY);
 
 	/* Release DIG link encoder resources before running assignment algorithm. */
 	for (i = 0; i < dc->current_state->stream_count; i++)
···
 	return link_enc;
 }
 
+struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream_current(
+		struct dc *dc,
+		const struct dc_stream_state *stream)
+{
+	struct link_encoder *link_enc = NULL;
+	struct display_endpoint_id ep_id;
+	int i;
+
+	ep_id = (struct display_endpoint_id) {
+		.link_id = stream->link->link_id,
+		.ep_type = stream->link->ep_type};
+
+	for (i = 0; i < MAX_PIPES; i++) {
+		struct link_enc_assignment assignment =
+			dc->current_state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[i];
+
+		if (assignment.valid == true && are_ep_ids_equal(&assignment.ep_id, &ep_id)) {
+			link_enc = stream->link->dc->res_pool->link_encoders[assignment.eng_id - ENGINE_ID_DIGA];
+			break;
+		}
+	}
+
+	return link_enc;
+}
+
 bool link_enc_cfg_is_link_enc_avail(struct dc *dc, enum engine_id eng_id, struct dc_link *link)
 {
 	bool is_avail = true;
···
 	uint8_t dig_stream_count = 0;
 	int matching_stream_ptrs = 0;
 	int eng_ids_per_ep_id[MAX_PIPES] = {0};
+	int ep_ids_per_eng_id[MAX_PIPES] = {0};
 	int valid_bitmap = 0;
 
 	/* (1) No. valid entries same as stream count. */
···
 			struct display_endpoint_id ep_id_i = assignment_i.ep_id;
 
 			eng_ids_per_ep_id[i]++;
+			ep_ids_per_eng_id[i]++;
 			for (j = 0; j < MAX_PIPES; j++) {
 				struct link_enc_assignment assignment_j =
 					state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[j];
···
 							assignment_i.eng_id != assignment_j.eng_id) {
 						valid_uniqueness = false;
 						eng_ids_per_ep_id[i]++;
+					} else if (!are_ep_ids_equal(&ep_id_i, &ep_id_j) &&
+							assignment_i.eng_id == assignment_j.eng_id) {
+						valid_uniqueness = false;
+						ep_ids_per_eng_id[i]++;
 					}
 				}
 			}

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

···
 	if (pipe_ctx_old->stream->ctx->dc->res_pool->funcs->link_encs_assign) {
 		bool need_reprogram = false;
 		struct dc *dc = pipe_ctx_old->stream->ctx->dc;
-		enum link_enc_cfg_mode mode = dc->current_state->res_ctx.link_enc_cfg_ctx.mode;
+		struct link_encoder *link_enc_prev =
+			link_enc_cfg_get_link_enc_used_by_stream_current(dc, pipe_ctx_old->stream);
 
-		dc->current_state->res_ctx.link_enc_cfg_ctx.mode = LINK_ENC_CFG_STEADY;
-		if (link_enc_cfg_get_link_enc_used_by_stream(dc, pipe_ctx_old->stream) != pipe_ctx->stream->link_enc)
+		if (link_enc_prev != pipe_ctx->stream->link_enc)
 			need_reprogram = true;
-		dc->current_state->res_ctx.link_enc_cfg_ctx.mode = mode;
 
 		return need_reprogram;
 	}

drivers/gpu/drm/amd/display/dc/inc/link_enc_cfg.h

···
 /* Return DIG link encoder. NULL if unused. */
 struct link_encoder *link_enc_cfg_get_link_enc(const struct dc_link *link);
 
+/* Return DIG link encoder used by stream in current/previous state. NULL if unused. */
+struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream_current(
+		struct dc *dc,
+		const struct dc_stream_state *stream);
+
 /* Return true if encoder available to use. */
 bool link_enc_cfg_is_link_enc_avail(struct dc *dc, enum engine_id eng_id, struct dc_link *link);