[PATCH 1/5] drm/amd/display: Retry link training again

[Bhawanpreet Lakha]

[Why]
Some receivers seem to fail the first link training but are good on
subsequent tries. We want to retry link training again. This fixes
HTC vive pro not lighting up after being disabled.

[How]
Check if the link training passed without fall back if this is not
the case then we retry link training.

Change-Id: Idd7232d9954af863f4d443984b209d87c9d91a30
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland at amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c    | 20 ++++++++++++++++++--
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c |  5 ++++-
 drivers/gpu/drm/amd/display/dc/inc/dc_link_dp.h  |  3 ++-
 3 files changed, 24 insertions(+), 4 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 0adaabcbd984..b180197a41e2 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 +767,16 @@ bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 				 */
 
 				/* deal with non-mst cases */
-				dp_verify_link_cap(link, &link->reported_link_cap);
+				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;
+				}
 			}
 
 			/* 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 b9db6e69e9c3..e8a69d7312c8 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_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};
@@ -1160,6 +1161,8 @@ bool dp_verify_link_cap(
 							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 697b5ee73845..a37255c757e0 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_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