drm/amd/display: Add hook for MST root branch info

This allows DM to do any necessary updates before MST discovery starts.
Signed-off-by: NNikola Cornij <nikola.cornij@amd.com>
Reviewed-by: NNikola Cornij <Nikola.Cornij@amd.com>
Acked-by: NLeo Li <sunpeng.li@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -169,6 +169,11 @@ static void get_payload_table(
 	mutex_unlock(&mst_mgr->payload_lock);
 }
 
+void dm_helpers_dp_update_branch_info(
+	struct dc_context *ctx,
+	const struct dc_link *link)
+{}
+
 /*
  * Writes payload allocation table in immediate downstream device.
  */

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -529,6 +529,10 @@ static bool detect_dp(
 			if (reason == DETECT_REASON_BOOT)
 				boot = true;
 
+			dm_helpers_dp_update_branch_info(
+				link->ctx,
+				link);
+
 			if (!dm_helpers_dp_mst_start_top_mgr(
 				link->ctx,
 				link, boot)) {

drivers/gpu/drm/amd/display/dc/dm_helpers.h

@@ -40,6 +40,14 @@ enum dc_edid_status dm_helpers_parse_edid_caps(
 	const struct dc_edid *edid,
 	struct dc_edid_caps *edid_caps);
 
+
+/*
+ * Update DP branch info
+ */
+void dm_helpers_dp_update_branch_info(
+		struct dc_context *ctx,
+		const struct dc_link *link);
+
 /*
  * Writes payload allocation table in immediate downstream device.
  */