drm/display/dp_mst: Fix payload addition on a disconnected sink

If an MST stream is enabled on a disconnected sink, the payload for the
stream is not created and the MST manager's payload count/next start VC
slot is not updated. Since the payload's start VC slot may still contain
a valid value (!= -1) the subsequent disabling of such a stream could
cause an incorrect decrease of the payload count/next start VC slot in
drm_dp_remove_payload() and hence later payload additions will fail.

Fix the above by marking the payload as invalid in the above case, so
that it's skipped during payload removal. While at it add a debug print
for this case.

Cc: Lyude Paul <lyude@redhat.com>
Cc: <stable@vger.kernel.org> # v6.1+
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221214184258.2869417-3-imre.deak@intel.com

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 01350510244f2f47b495a3f817be534e791586a1..5861b0a6247bc1bb10d5ae4dda45f27f537750d8 100644 (file)
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3309,8 +3309,13 @@ int drm_dp_add_payload_part1(struct drm_dp_mst_topology_mgr *mgr,
        int ret;
 
        port = drm_dp_mst_topology_get_port_validated(mgr, payload->port);
-       if (!port)
+       if (!port) {
+               drm_dbg_kms(mgr->dev,
+                           "VCPI %d for port %p not in topology, not creating a payload\n",
+                           payload->vcpi, payload->port);
+               payload->vc_start_slot = -1;
                return 0;
+       }
 
        if (mgr->payload_count == 0)
                mgr->next_start_slot = mst_state->start_slot;