drm/dp-mst: Remove tx_down_in_progress

Just replicates whether the list is empty or not. Nuke code
to avoid writing docs for it!

Cc: Dave Airlie <airlied@redhat.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1468612088-9721-6-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1493,11 +1493,8 @@ static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
 	WARN_ON(!mutex_is_locked(&mgr->qlock));
 
 	/* construct a chunk from the first msg in the tx_msg queue */
-	if (list_empty(&mgr->tx_msg_downq)) {
-		mgr->tx_down_in_progress = false;
+	if (list_empty(&mgr->tx_msg_downq))
 		return;
-	}
-	mgr->tx_down_in_progress = true;
 
 	txmsg = list_first_entry(&mgr->tx_msg_downq, struct drm_dp_sideband_msg_tx, next);
 	ret = process_single_tx_qlock(mgr, txmsg, false);
@@ -1512,10 +1509,6 @@ static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
 		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
 		wake_up(&mgr->tx_waitq);
 	}
-	if (list_empty(&mgr->tx_msg_downq)) {
-		mgr->tx_down_in_progress = false;
-		return;
-	}
 }
 
 /* called holding qlock */
@@ -1538,7 +1531,7 @@ static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
 {
 	mutex_lock(&mgr->qlock);
 	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);
-	if (!mgr->tx_down_in_progress)
+	if (list_is_singular(&mgr->tx_msg_downq))
 		process_single_down_tx_qlock(mgr);
 	mutex_unlock(&mgr->qlock);
 }
@@ -2887,7 +2880,7 @@ static void drm_dp_tx_work(struct work_struct *work)
 	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, tx_work);
 
 	mutex_lock(&mgr->qlock);
-	if (mgr->tx_down_in_progress)
+	if (!list_empty(&mgr->tx_msg_downq))
 		process_single_down_tx_qlock(mgr);
 	mutex_unlock(&mgr->qlock);
 }

include/drm/drm_dp_mst_helper.h

@@ -446,7 +446,6 @@ struct drm_dp_mst_topology_mgr {
 	   the mstb tx_slots and txmsg->state once they are queued */
 	struct mutex qlock;
 	struct list_head tx_msg_downq;
-	bool tx_down_in_progress;
 
 	/* payload info + lock for it */
 	struct mutex payload_lock;