drm/amd/display: Don't skip link training for empty dongle

[Why]
Skipping initial link training will result in no verified link cap for
mode enumeration. Some versions of the BIOS seem to have PHY programming
sequence issue as well if initial link training is skipped, resulting in
a softlock in BIOS command table.

[How]
Identify the empty dongle hotplug case, and still do initial link
training.

Signed-off-by: Eric Yang <[email protected]>
Reviewed-by: Tony Cheng <[email protected]>
Acked-by: Leo Li <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

1 files changed, 16 insertions, 2 deletions

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index 564f140d4e60..9f551fc68622 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -706,12 +706,26 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 				if (memcmp(&link->dpcd_caps, &prev_dpcd_caps, sizeof(struct dpcd_caps)))
 					same_dpcd = false;
 			}
-			/* Active dongle downstream unplug */
+			/* Active dongle plug in without display or downstream unplug*/
 			if (link->type == dc_connection_active_dongle
 					&& link->dpcd_caps.sink_count.
 					bits.SINK_COUNT == 0) {
-				if (prev_sink != NULL)
+				if (prev_sink != NULL) {
+					/* Downstream unplug */
 					dc_sink_release(prev_sink);
+				} else {
+					/* Empty dongle plug in */
+					for (i = 0; i < LINK_TRAINING_MAX_VERIFY_RETRY; i++) {
+						int fail_count = 0;
+
+						dp_verify_link_cap(link,
+								  &link->reported_link_cap,
+								  &fail_count);
+
+						if (fail_count == 0)
+							break;
+					}
+				}
 				return true;
 			}