[PATCH 28/77] drm/amd/display: Fix two MST not light up regressions

[Harry Wentland]

From: Jerry Zuo <Jerry.Zuo at amd.com>

1. Change 100104: Move verify link cap after read edid causes MST
   link_cap struct not being set. It leads to zero denominator
   pbn_per_slot value, leading to the crash at
   dal_fixed31_32_div(). Skip MST link training for now and will
   need to add MST specific link traning routine later.

2. Change 98822: Adding edp supports changes link setting
   condition from max_link to verified_link. It leads to MST is
   getting wrong link settings.
   e.g. LINK_SPREAD_05_DOWNSPREAD_30KHZ not set in MST case

Signed-off-by: Jerry Zuo <Jerry.Zuo at amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng at amd.com>
Acked-by: Harry Wentland <Harry.Wentland at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c    | 16 +++++++++-------
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c |  8 ++++++++
 2 files changed, 17 insertions(+), 7 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 cab54afa1131..ee9b98472029 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -607,6 +607,12 @@ bool dc_link_detect(struct dc_link *link, bool boot)
 			if (link->type == dc_connection_mst_branch) {
 				LINK_INFO("link=%d, mst branch is now Connected\n",
 					link->link_index);
+				/* Need to setup mst link_cap struct here
+				 * otherwise dc_link_detect() will leave mst link_cap
+				 * empty which leads to allocate_mst_payload() has "0"
+				 * pbn_per_slot value leading to exception on dal_fixed31_32_div()
+				 */
+				link->verified_link_cap = link->reported_link_cap;
 				return false;
 			}
 
@@ -672,13 +678,9 @@ bool dc_link_detect(struct dc_link *link, bool boot)
 			 * TODO debug why Dell 2413 doesn't like
 			 *  two link trainings
 			 */
-			if (is_mst_supported(link)) {
-				link->verified_link_cap =
-						link->reported_link_cap;
-			} else {
-				dp_hbr_verify_link_cap(link,
-				    &link->reported_link_cap);
-			}
+
+			/* deal with non-mst cases */
+			dp_hbr_verify_link_cap(link, &link->reported_link_cap);
 		}
 
 		/* 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 d621237e923e..e35bdce6a0f3 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
@@ -1459,6 +1459,14 @@ void decide_link_settings(struct dc_stream_state *stream,
 		return;
 	}
 
+	/* MST doesn't perform link training for now
+	 * TODO: add MST specific link training routine
+	 */
+	if (is_mst_supported(link)) {
+		*link_setting = link->verified_link_cap;
+		return;
+	}
+
     /* search for the minimum link setting that:
      * 1. is supported according to the link training result
      * 2. could support the b/w requested by the timing
-- 
2.11.0