[PATCH AUTOSEL 4.18 52/92] drm/amd/display: support access ddc for mst branch

[Sasha Levin]

From: Eric Yang <Eric.Yang2@xxxxxxx>

[ Upstream commit 0a14544661fad1606cc96aece30b2950fd9c4c81 ]

[Why]
Megachip dockings accesses ddc line through display driver when
installing FW. Previously, we would fail every transaction because
link attached to mst branch did not have their ddc transaction type
set.

[How]
Set ddc transaction type when mst branch is connected.

Signed-off-by: Eric Yang <Eric.Yang2@xxxxxxx>
Reviewed-by: Charlene Liu <Charlene.Liu@xxxxxxx>
Acked-by: Harry Wentland <harry.wentland@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 4 ++++
 1 file changed, 4 insertions(+)

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 2fa521812d23..0351f7dc46e3 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -497,6 +497,10 @@ static bool detect_dp(
 			sink_caps->signal = SIGNAL_TYPE_DISPLAY_PORT_MST;
 			link->type = dc_connection_mst_branch;
 
+			dal_ddc_service_set_transaction_type(
+							link->ddc,
+							sink_caps->transaction_type);
+
 			/*
 			 * This call will initiate MST topology discovery. Which
 			 * will detect MST ports and add new DRM connector DRM
-- 
2.17.1