drm/amd/display: Fix DP MST sinks removal issue

[Why]
In USB4 DP tunneling, it's possible to have this scenario that
the path becomes unavailable and CM tears down the path a little bit late.
So, in this case, the HPD is high but fails to read any DPCD register.
That causes the link connection type to be set to sst.
And not all sinks are removed behind the MST branch.

[How]
Restore the link connection type if it fails to read DPCD register.

Cc: [email protected]
Cc: Mario Limonciello <[email protected]>
Reviewed-by: Wenjing Liu <[email protected]>
Acked-by: Qingqing Zhuo <[email protected]>
Signed-off-by: Cruise Hung <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: Cruise Hung

drivers/gpu/drm/amd/display/dc/link/link_detection.c

@@ -855,6 +855,7 @@ static bool detect_link_and_local_sink(struct dc_link *link,
 	struct dc_sink *prev_sink = NULL;
 	struct dpcd_caps prev_dpcd_caps;
 	enum dc_connection_type new_connection_type = dc_connection_none;
+	enum dc_connection_type pre_connection_type = link->type;
 	const uint32_t post_oui_delay = 30; // 30ms
 
 	DC_LOGGER_INIT(link->ctx->logger);
@@ -957,6 +958,8 @@ static bool detect_link_and_local_sink(struct dc_link *link,
 			}
 
 			if (!detect_dp(link, &sink_caps, reason)) {
+				link->type = pre_connection_type;
+
 				if (prev_sink)
 					dc_sink_release(prev_sink);
 				return false;
@@ -1244,11 +1247,16 @@ bool link_detect(struct dc_link *link, enum dc_detect_reason reason)
 	bool is_delegated_to_mst_top_mgr = false;
 	enum dc_connection_type pre_link_type = link->type;
 
+	DC_LOGGER_INIT(link->ctx->logger);
+
 	is_local_sink_detect_success = detect_link_and_local_sink(link, reason);
 
 	if (is_local_sink_detect_success && link->local_sink)
 		verify_link_capability(link, link->local_sink, reason);
 
+	DC_LOG_DC("%s: link_index=%d is_local_sink_detect_success=%d pre_link_type=%d link_type=%d\n", __func__,
+				link->link_index, is_local_sink_detect_success, pre_link_type, link->type);
+
 	if (is_local_sink_detect_success && link->local_sink &&
 			dc_is_dp_signal(link->local_sink->sink_signal) &&
 			link->dpcd_caps.is_mst_capable)