drm/dp_mst: Do not set proposed vcpi directly

[Why]
When we receive CSN message to notify one port is disconnected, we will
implicitly set its corresponding num_slots to 0. Later on, we will
eventually call drm_dp_update_payload_part1() to arrange down streams.

In drm_dp_update_payload_part1(), we iterate over all proposed_vcpis[]
to do the update. Not specific to a target sink only. For example, if we
light up 2 monitors, Monitor_A and Monitor_B, and then we unplug
Monitor_B. Later on, when we call drm_dp_update_payload_part1() to try
to update payload for Monitor_A, we'll also implicitly clean payload for
Monitor_B at the same time. And finally, when we try to call
drm_dp_update_payload_part1() to clean payload for Monitor_B, we will do
nothing at this time since payload for Monitor_B has been cleaned up
previously.

For StarTech 1to3 DP hub, it seems like if we didn't update DPCD payload
ID table then polling for "ACT Handled"(BIT_1 of DPCD 002C0h) will fail
and this polling will last for 3 seconds.

Therefore, guess the best way is we don't set the proposed_vcpi[]
diretly. Let user of these herlper functions to set the proposed_vcpi
directly.

[How]
1. Revert commit 7617e96 ("drm/dp_mst: clear time slots for ports
invalid")
2. Tackle the issue in previous commit by skipping those trasient
proposed VCPIs. These stale VCPIs shoulde be explicitly cleared by
user later on.

Changes since v1:
* Change debug macro to use drm_dbg_kms() instead
* Amend the commit message to add Fixed & Cc tags

Signed-off-by: Wayne Lin <[email protected]>
Fixes: 7617e96 ("drm/dp_mst: clear time slots for ports invalid")
Cc: Lyude Paul <[email protected]>
Cc: Wayne Lin <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: [email protected]
Cc: <[email protected]> # v5.5+
Signed-off-by: Lyude Paul <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Lyude Paul <[email protected]>

Author: Wayne Lin

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -2501,7 +2501,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 {
 	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
 	struct drm_dp_mst_port *port;
-	int old_ddps, old_input, ret, i;
+	int old_ddps, ret;
 	u8 new_pdt;
 	bool new_mcs;
 	bool dowork = false, create_connector = false;
@@ -2533,7 +2533,6 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 	}
 
 	old_ddps = port->ddps;
-	old_input = port->input;
 	port->input = conn_stat->input_port;
 	port->ldps = conn_stat->legacy_device_plug_status;
 	port->ddps = conn_stat->displayport_device_plug_status;
@@ -2555,28 +2554,6 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 		dowork = false;
 	}
 
-	if (!old_input && old_ddps != port->ddps && !port->ddps) {
-		for (i = 0; i < mgr->max_payloads; i++) {
-			struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
-			struct drm_dp_mst_port *port_validated;
-
-			if (!vcpi)
-				continue;
-
-			port_validated =
-				container_of(vcpi, struct drm_dp_mst_port, vcpi);
-			port_validated =
-				drm_dp_mst_topology_get_port_validated(mgr, port_validated);
-			if (!port_validated) {
-				mutex_lock(&mgr->payload_lock);
-				vcpi->num_slots = 0;
-				mutex_unlock(&mgr->payload_lock);
-			} else {
-				drm_dp_mst_topology_put_port(port_validated);
-			}
-		}
-	}
-
 	if (port->connector)
 		drm_modeset_unlock(&mgr->base.lock);
 	else if (create_connector)
@@ -3410,8 +3387,15 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 				port = drm_dp_mst_topology_get_port_validated(
 				    mgr, port);
 				if (!port) {
-					mutex_unlock(&mgr->payload_lock);
-					return -EINVAL;
+					if (vcpi->num_slots == payload->num_slots) {
+						cur_slots += vcpi->num_slots;
+						payload->start_slot = req_payload.start_slot;
+						continue;
+					} else {
+						drm_dbg_kms("Fail:set payload to invalid sink");
+						mutex_unlock(&mgr->payload_lock);
+						return -EINVAL;
+					}
 				}
 				put_port = true;
 			}