drm/amd/display: Do not skip link training on DP quick hot plug

[Why]
When rapidly plugging and unplugging a DP sink, detection link
training can be mistakenly skipped.

This is due to the hotplug processing occurring before the
encoder assignment logic has had a chance to process the removal
of a stream. The encoder that would be used for detection link
training is then erroneously reported as already in use and
detection link training is skipped.

[How]
During hot plug processing, only determine a link encoder to be
unavailable for a particular link if it has been assigned to a
different link.
Reviewed-by: Meenakshikumar Somasundaram <Meenakshikumar.Somasundaram@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Agustin Gutierrez Sanchez <agustin.gutierrez@amd.com>
Signed-off-by: Jimmy Kizito <Jimmy.Kizito@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/core/dc_link_dp.c

@@ -2863,7 +2863,7 @@ bool dp_verify_link_cap(
 		link->verified_link_cap = *known_limit_link_setting;
 		return true;
 	} else if (link->link_enc && link->dc->res_pool->funcs->link_encs_assign &&
-			!link_enc_cfg_is_link_enc_avail(link->ctx->dc, link->link_enc->preferred_engine)) {
+			!link_enc_cfg_is_link_enc_avail(link->ctx->dc, link->link_enc->preferred_engine, link)) {
 		link->verified_link_cap = initial_link_settings;
 		return true;
 	}

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

@@ -488,16 +488,19 @@ struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream(
 	return link_enc;
 }
 
-bool link_enc_cfg_is_link_enc_avail(struct dc *dc, enum engine_id eng_id)
+bool link_enc_cfg_is_link_enc_avail(struct dc *dc, enum engine_id eng_id, struct dc_link *link)
 {
 	bool is_avail = true;
 	int i;
 
-	/* Add assigned encoders to list. */
+	/* An encoder is not available if it has already been assigned to a different endpoint. */
 	for (i = 0; i < MAX_PIPES; i++) {
 		struct link_enc_assignment assignment = get_assignment(dc, i);
+		struct display_endpoint_id ep_id = (struct display_endpoint_id) {
+				.link_id = link->link_id,
+				.ep_type = link->ep_type};
 
-		if (assignment.valid && assignment.eng_id == eng_id) {
+		if (assignment.valid && assignment.eng_id == eng_id && !are_ep_ids_equal(&ep_id, &assignment.ep_id)) {
 			is_avail = false;
 			break;
 		}

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

@@ -97,7 +97,7 @@ struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream(
 		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);
+bool link_enc_cfg_is_link_enc_avail(struct dc *dc, enum engine_id eng_id, struct dc_link *link);
 
 /* Returns true if encoder assignments in supplied state pass validity checks. */
 bool link_enc_cfg_validate(struct dc *dc, struct dc_state *state);