drm/display/dp_mst: Fix down/up message handling after sink disconnect

If the sink gets disconnected during receiving a multi-packet DP MST AUX
down-reply/up-request sideband message, the state keeping track of which
packets have been received already is not reset. This results in a failed
sanity check for the subsequent message packet received after a sink is
reconnected (due to the pending message not yet completed with an
end-of-message-transfer packet), indicated by the

"sideband msg set header failed"

error.

Fix the above by resetting the up/down message reception state after a
disconnect event.

Cc: Lyude Paul <[email protected]>
Cc: <[email protected]> # v3.17+
Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: Lyude Paul <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -3641,6 +3641,9 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 		drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
 		ret = 0;
 		mgr->payload_id_table_cleared = false;
+
+		memset(&mgr->down_rep_recv, 0, sizeof(mgr->down_rep_recv));
+		memset(&mgr->up_req_recv, 0, sizeof(mgr->up_req_recv));
 	}
 
 out_unlock: