[PATCH] drm/amd/display: Retry link training if preferred settings not used

[Bhawanpreet Lakha]

Some receivers seem to fail the first link training but are good on
subsequent tries. Check if the max setting was good otherwise retry
link training.

This fixes HTC vive pro issue where it would fail to light up after
being disabled.

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c    | 21 +++++++++++++++++++--
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c |  9 ++++++---
 drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h  |  3 ++-
 3 files changed, 27 insertions(+), 6 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 4de68fa074a0..34ab1a91baab 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -60,7 +60,14 @@
 
 enum {
 	LINK_RATE_REF_FREQ_IN_MHZ = 27,
-	PEAK_FACTOR_X1000 = 1006
+	PEAK_FACTOR_X1000 = 1006,
+	/*
+	 * Some receivers fail to train on first try and are good
+	 * on subsequent tries. 2 retries should be plenty. If we
+	 * don't have a successful training then we don't expect to
+	 * ever get one.
+	 */
+	LINK_TRAINING_MAX_VERIFY_RETRY = 2
 };
 
 /*******************************************************************************
@@ -760,7 +767,17 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 				 */
 
 				/* deal with non-mst cases */
-				dp_hbr_verify_link_cap(link, &link->reported_link_cap);
+				for (i = 0; i < LINK_TRAINING_MAX_VERIFY_RETRY; i++) {
+					int fail_count = 0;
+
+					dp_hbr_verify_link_cap(link,
+							      &link->reported_link_cap,
+							      &fail_count);
+
+					if (fail_count == 0)
+						break;
+				}
+
 			}
 
 			/* HDMI-DVI Dongle */
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index 8fbb999e4a8a..18258944f442 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -1088,7 +1088,8 @@ static struct dc_link_settings get_max_link_cap(struct dc_link *link)
 
 bool dp_hbr_verify_link_cap(
 	struct dc_link *link,
-	struct dc_link_settings *known_limit_link_setting)
+	struct dc_link_settings *known_limit_link_setting,
+	int *fail_count)
 {
 	struct dc_link_settings max_link_cap = {0};
 	struct dc_link_settings cur_link_setting = {0};
@@ -1146,15 +1147,17 @@ bool dp_hbr_verify_link_cap(
 				cur);
 
 
-		if (skip_link_training)
+		if (skip_link_training) {
 			success = true;
-		else {
+		} else {
 			status = dc_link_dp_perform_link_training(
 							link,
 							cur,
 							skip_video_pattern);
 			if (status == LINK_TRAINING_SUCCESS)
 				success = true;
+			else
+				(*fail_count)++;
 		}
 
 		if (success)
diff --git a/drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h b/drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h
index 2f783c650084..5eed19153de5 100644
--- a/drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h
+++ b/drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h
@@ -35,7 +35,8 @@ struct dc_link_settings;
 
 bool dp_hbr_verify_link_cap(
 	struct dc_link *link,
-	struct dc_link_settings *known_limit_link_setting);
+	struct dc_link_settings *known_limit_link_setting,
+	int *fail_count);
 
 bool dp_validate_mode_timing(
 	struct dc_link *link,
-- 
2.14.1