drm/dp_mst: Remove single tx msg restriction.

Now that we can support multiple simultaneous replies, remove the
restrictions placed on sending new tx msgs.

This patch essentially just reverts commit
5a64967a2f3b ("drm/dp_mst: Have DP_Tx send one msg at a time")
now that the problem is solved in a different way.

Cc: Wayne Lin <[e-mail]>
Reviewed-by: Lyude Paul <[e-mail]>
Reviewed-by: Wayne Lin <[e-mail]>
Signed-off-by: Sean Paul <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_dp_mst_topology.c

···
 		    txmsg->state == DRM_DP_SIDEBAND_TX_SENT) {
 			mstb->tx_slots[txmsg->seqno] = NULL;
 		}
-		mgr->is_waiting_for_dwn_reply = false;
-
 	}
 out:
 	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
···
 	}
 	mutex_unlock(&mgr->qlock);
 
-	drm_dp_mst_kick_tx(mgr);
 	return ret;
 }
 
···
 	ret = process_single_tx_qlock(mgr, txmsg, false);
 	if (ret == 1) {
 		/* txmsg is sent it should be in the slots now */
-		mgr->is_waiting_for_dwn_reply = true;
 		list_del(&txmsg->next);
 	} else if (ret) {
 		DRM_DEBUG_KMS("failed to send msg in q %d\n", ret);
-		mgr->is_waiting_for_dwn_reply = false;
 		list_del(&txmsg->next);
 		if (txmsg->seqno != -1)
 			txmsg->dst->tx_slots[txmsg->seqno] = NULL;
···
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
 	}
 
-	if (list_is_singular(&mgr->tx_msg_downq) &&
-	    !mgr->is_waiting_for_dwn_reply)
+	if (list_is_singular(&mgr->tx_msg_downq))
 		process_single_down_tx_qlock(mgr);
 	mutex_unlock(&mgr->qlock);
 }
···
 	mutex_lock(&mgr->qlock);
 	txmsg->state = DRM_DP_SIDEBAND_TX_RX;
 	mstb->tx_slots[seqno] = NULL;
-	mgr->is_waiting_for_dwn_reply = false;
 	mutex_unlock(&mgr->qlock);
 
 	wake_up_all(&mgr->tx_waitq);
···
 	return 0;
 
 out_clear_reply:
-	mutex_lock(&mgr->qlock);
-	mgr->is_waiting_for_dwn_reply = false;
-	mutex_unlock(&mgr->qlock);
 	if (msg)
 		memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
 out:
···
 	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, tx_work);
 
 	mutex_lock(&mgr->qlock);
-	if (!list_empty(&mgr->tx_msg_downq) && !mgr->is_waiting_for_dwn_reply)
+	if (!list_empty(&mgr->tx_msg_downq))
 		process_single_down_tx_qlock(mgr);
 	mutex_unlock(&mgr->qlock);
 }

include/drm/drm_dp_mst_helper.h

···
 	bool payload_id_table_cleared : 1;
 
 	/**
-	 * @is_waiting_for_dwn_reply: whether we're waiting for a down reply.
-	 */
-	bool is_waiting_for_dwn_reply : 1;
-
-	/**
 	 * @mst_primary: Pointer to the primary/first branch device.
 	 */
 	struct drm_dp_mst_branch *mst_primary;