diff --git a/drivers/infiniband/hw/cxgb4/device.c b/drivers/infiniband/hw/cxgb4/device.c
index 8483111..9062ed9 100644
--- a/drivers/infiniband/hw/cxgb4/device.c
+++ b/drivers/infiniband/hw/cxgb4/device.c
@@ -44,6 +44,12 @@ MODULE_DESCRIPTION("Chelsio T4 RDMA Driver");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_VERSION(DRV_VERSION);
 
+struct uld_ctx {
+	struct list_head entry;
+	struct cxgb4_lld_info lldi;
+	struct c4iw_dev *dev;
+};
+
 static LIST_HEAD(uld_ctx_list);
 static DEFINE_MUTEX(dev_mutex);
 
@@ -263,6 +269,9 @@ static int stats_show(struct seq_file *seq, void *v)
 	seq_printf(seq, "  OCQPMEM: %10llu %10llu %10llu\n",
 			dev->rdev.stats.ocqp.total, dev->rdev.stats.ocqp.cur,
 			dev->rdev.stats.ocqp.max);
+	seq_printf(seq, "  DB FULL: %10llu\n", dev->rdev.stats.db_full);
+	seq_printf(seq, " DB EMPTY: %10llu\n", dev->rdev.stats.db_empty);
+	seq_printf(seq, "  DB DROP: %10llu\n", dev->rdev.stats.db_drop);
 	return 0;
 }
 
@@ -283,6 +292,9 @@ static ssize_t stats_clear(struct file *file, const char __user *buf,
 	dev->rdev.stats.pbl.max = 0;
 	dev->rdev.stats.rqt.max = 0;
 	dev->rdev.stats.ocqp.max = 0;
+	dev->rdev.stats.db_full = 0;
+	dev->rdev.stats.db_empty = 0;
+	dev->rdev.stats.db_drop = 0;
 	mutex_unlock(&dev->rdev.stats.lock);
 	return count;
 }
@@ -443,12 +455,6 @@ static void c4iw_rdev_close(struct c4iw_rdev *rdev)
 	c4iw_destroy_resource(&rdev->resource);
 }
 
-struct uld_ctx {
-	struct list_head entry;
-	struct cxgb4_lld_info lldi;
-	struct c4iw_dev *dev;
-};
-
 static void c4iw_dealloc(struct uld_ctx *ctx)
 {
 	c4iw_rdev_close(&ctx->dev->rdev);
@@ -514,6 +520,7 @@ static struct c4iw_dev *c4iw_alloc(const struct cxgb4_lld_info *infop)
 	idr_init(&devp->mmidr);
 	spin_lock_init(&devp->lock);
 	mutex_init(&devp->rdev.stats.lock);
+	mutex_init(&devp->db_mutex);
 
 	if (c4iw_debugfs_root) {
 		devp->debugfs_root = debugfs_create_dir(
@@ -659,11 +666,76 @@ static int c4iw_uld_state_change(void *handle, enum cxgb4_state new_state)
 	return 0;
 }
 
+static int disable_qp_db(int id, void *p, void *data)
+{
+	struct c4iw_qp *qp = p;
+
+	t4_disable_wq_db(&qp->wq);
+	return 0;
+}
+
+static void stop_queues(struct uld_ctx *ctx)
+{
+	spin_lock_irq(&ctx->dev->lock);
+	ctx->dev->db_state = FLOW_CONTROL;
+	idr_for_each(&ctx->dev->qpidr, disable_qp_db, NULL);
+	spin_unlock_irq(&ctx->dev->lock);
+}
+
+static int enable_qp_db(int id, void *p, void *data)
+{
+	struct c4iw_qp *qp = p;
+
+	t4_enable_wq_db(&qp->wq);
+	return 0;
+}
+
+static void resume_queues(struct uld_ctx *ctx)
+{
+	spin_lock_irq(&ctx->dev->lock);
+	ctx->dev->db_state = NORMAL;
+	idr_for_each(&ctx->dev->qpidr, enable_qp_db, NULL);
+	spin_unlock_irq(&ctx->dev->lock);
+}
+
+static int c4iw_uld_control(void *handle, enum cxgb4_control control, ...)
+{
+	struct uld_ctx *ctx = handle;
+
+	switch (control) {
+	case CXGB4_CONTROL_DB_FULL:
+		stop_queues(ctx);
+		mutex_lock(&ctx->dev->rdev.stats.lock);
+		ctx->dev->rdev.stats.db_full++;
+		mutex_unlock(&ctx->dev->rdev.stats.lock);
+		break;
+	case CXGB4_CONTROL_DB_EMPTY:
+		resume_queues(ctx);
+		mutex_lock(&ctx->dev->rdev.stats.lock);
+		ctx->dev->rdev.stats.db_empty++;
+		mutex_unlock(&ctx->dev->rdev.stats.lock);
+		break;
+	case CXGB4_CONTROL_DB_DROP:
+		printk(KERN_WARNING MOD "%s: Fatal DB DROP\n",
+		       pci_name(ctx->lldi.pdev));
+		mutex_lock(&ctx->dev->rdev.stats.lock);
+		ctx->dev->rdev.stats.db_drop++;
+		mutex_unlock(&ctx->dev->rdev.stats.lock);
+		break;
+	default:
+		printk(KERN_WARNING MOD "%s: unknown control cmd %u\n",
+		       pci_name(ctx->lldi.pdev), control);
+		break;
+	}
+	return 0;
+}
+
 static struct cxgb4_uld_info c4iw_uld_info = {
 	.name = DRV_NAME,
 	.add = c4iw_uld_add,
 	.rx_handler = c4iw_uld_rx_handler,
 	.state_change = c4iw_uld_state_change,
+	.control = c4iw_uld_control,
 };
 
 static int __init c4iw_init_module(void)
diff --git a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
index ec7c848..1924c19 100644
--- a/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
+++ b/drivers/infiniband/hw/cxgb4/iw_cxgb4.h
@@ -117,6 +117,9 @@ struct c4iw_stats {
 	struct c4iw_stat pbl;
 	struct c4iw_stat rqt;
 	struct c4iw_stat ocqp;
+	u64  db_full;
+	u64  db_empty;
+	u64  db_drop;
 };
 
 struct c4iw_rdev {
@@ -192,6 +195,12 @@ static inline int c4iw_wait_for_reply(struct c4iw_rdev *rdev,
 	return wr_waitp->ret;
 }
 
+enum db_state {
+	NORMAL = 0,
+	FLOW_CONTROL = 1,
+	RECOVERY = 2
+};
+
 struct c4iw_dev {
 	struct ib_device ibdev;
 	struct c4iw_rdev rdev;
@@ -200,7 +209,9 @@ struct c4iw_dev {
 	struct idr qpidr;
 	struct idr mmidr;
 	spinlock_t lock;
+	struct mutex db_mutex;
 	struct dentry *debugfs_root;
+	enum db_state db_state;
 };
 
 static inline struct c4iw_dev *to_c4iw_dev(struct ib_device *ibdev)
@@ -228,8 +239,8 @@ static inline struct c4iw_mr *get_mhp(struct c4iw_dev *rhp, u32 mmid)
 	return idr_find(&rhp->mmidr, mmid);
 }
 
-static inline int insert_handle(struct c4iw_dev *rhp, struct idr *idr,
-				void *handle, u32 id)
+static inline int _insert_handle(struct c4iw_dev *rhp, struct idr *idr,
+				 void *handle, u32 id, int lock)
 {
 	int ret;
 	int newid;
@@ -237,15 +248,29 @@ static inline int insert_handle(struct c4iw_dev *rhp, struct idr *idr,
 	do {
 		if (!idr_pre_get(idr, GFP_KERNEL))
 			return -ENOMEM;
-		spin_lock_irq(&rhp->lock);
+		if (lock)
+			spin_lock_irq(&rhp->lock);
 		ret = idr_get_new_above(idr, handle, id, &newid);
 		BUG_ON(newid != id);
-		spin_unlock_irq(&rhp->lock);
+		if (lock)
+			spin_unlock_irq(&rhp->lock);
 	} while (ret == -EAGAIN);
 
 	return ret;
 }
 
+static inline int insert_handle(struct c4iw_dev *rhp, struct idr *idr,
+				void *handle, u32 id)
+{
+	return _insert_handle(rhp, idr, handle, id, 1);
+}
+
+static inline int insert_handle_nolock(struct c4iw_dev *rhp, struct idr *idr,
+				       void *handle, u32 id)
+{
+	return _insert_handle(rhp, idr, handle, id, 0);
+}
+
 static inline void remove_handle(struct c4iw_dev *rhp, struct idr *idr, u32 id)
 {
 	spin_lock_irq(&rhp->lock);
@@ -369,6 +394,8 @@ struct c4iw_qp_attributes {
 	struct c4iw_ep *llp_stream_handle;
 	u8 layer_etype;
 	u8 ecode;
+	u16 sq_db_inc;
+	u16 rq_db_inc;
 };
 
 struct c4iw_qp {
@@ -443,6 +470,8 @@ static inline void insert_mmap(struct c4iw_ucontext *ucontext,
 
 enum c4iw_qp_attr_mask {
 	C4IW_QP_ATTR_NEXT_STATE = 1 << 0,
+	C4IW_QP_ATTR_SQ_DB = 1<<1,
+	C4IW_QP_ATTR_RQ_DB = 1<<2,
 	C4IW_QP_ATTR_ENABLE_RDMA_READ = 1 << 7,
 	C4IW_QP_ATTR_ENABLE_RDMA_WRITE = 1 << 8,
 	C4IW_QP_ATTR_ENABLE_RDMA_BIND = 1 << 9,
diff --git a/drivers/infiniband/hw/cxgb4/qp.c b/drivers/infiniband/hw/cxgb4/qp.c
index 74df98e..36fc94d 100644
--- a/drivers/infiniband/hw/cxgb4/qp.c
+++ b/drivers/infiniband/hw/cxgb4/qp.c
@@ -34,6 +34,10 @@
 
 #include "iw_cxgb4.h"
 
+static int db_delay_usecs = 1;
+module_param(db_delay_usecs, int, 0644);
+MODULE_PARM_DESC(db_delay_usecs, "Usecs to delay awaiting db fifo to drain");
+
 static int ocqp_support = 1;
 module_param(ocqp_support, int, 0644);
 MODULE_PARM_DESC(ocqp_support, "Support on-chip SQs (default=1)");
@@ -1117,6 +1121,29 @@ out:
 	return ret;
 }
 
+/*
+ * Called by the library when the qp has user dbs disabled due to
+ * a DB_FULL condition.  This function will single-thread all user
+ * DB rings to avoid overflowing the hw db-fifo.
+ */
+static int ring_kernel_db(struct c4iw_qp *qhp, u32 qid, u16 inc)
+{
+	int delay = db_delay_usecs;
+
+	mutex_lock(&qhp->rhp->db_mutex);
+	do {
+		if (cxgb4_dbfifo_count(qhp->rhp->rdev.lldi.ports[0], 1) < 768) {
+			writel(V_QID(qid) | V_PIDX(inc), qhp->wq.db);
+			break;
+		}
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		schedule_timeout(usecs_to_jiffies(delay));
+		delay = min(delay << 1, 200000);
+	} while (1);
+	mutex_unlock(&qhp->rhp->db_mutex);
+	return 0;
+}
+
 int c4iw_modify_qp(struct c4iw_dev *rhp, struct c4iw_qp *qhp,
 		   enum c4iw_qp_attr_mask mask,
 		   struct c4iw_qp_attributes *attrs,
@@ -1165,6 +1192,15 @@ int c4iw_modify_qp(struct c4iw_dev *rhp, struct c4iw_qp *qhp,
 		qhp->attr = newattr;
 	}
 
+	if (mask & C4IW_QP_ATTR_SQ_DB) {
+		ret = ring_kernel_db(qhp, qhp->wq.sq.qid, attrs->sq_db_inc);
+		goto out;
+	}
+	if (mask & C4IW_QP_ATTR_RQ_DB) {
+		ret = ring_kernel_db(qhp, qhp->wq.rq.qid, attrs->rq_db_inc);
+		goto out;
+	}
+
 	if (!(mask & C4IW_QP_ATTR_NEXT_STATE))
 		goto out;
 	if (qhp->attr.state == attrs->next_state)
@@ -1454,7 +1490,11 @@ struct ib_qp *c4iw_create_qp(struct ib_pd *pd, struct ib_qp_init_attr *attrs,
 	init_waitqueue_head(&qhp->wait);
 	atomic_set(&qhp->refcnt, 1);
 
-	ret = insert_handle(rhp, &rhp->qpidr, qhp, qhp->wq.sq.qid);
+	spin_lock_irq(&rhp->lock);
+	if (rhp->db_state != NORMAL)
+		t4_disable_wq_db(&qhp->wq);
+	ret = insert_handle_nolock(rhp, &rhp->qpidr, qhp, qhp->wq.sq.qid);
+	spin_unlock_irq(&rhp->lock);
 	if (ret)
 		goto err2;
 
@@ -1598,6 +1638,15 @@ int c4iw_ib_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr,
 			 C4IW_QP_ATTR_ENABLE_RDMA_WRITE |
 			 C4IW_QP_ATTR_ENABLE_RDMA_BIND) : 0;
 
+	/*
+	 * Use SQ_PSN and RQ_PSN to pass in IDX_INC values for
+	 * ringing the queue db when we're in DB_FULL mode.
+	 */
+	attrs.sq_db_inc = attr->sq_psn;
+	attrs.rq_db_inc = attr->rq_psn;
+	mask |= (attr_mask & IB_QP_SQ_PSN) ? C4IW_QP_ATTR_SQ_DB : 0;
+	mask |= (attr_mask & IB_QP_RQ_PSN) ? C4IW_QP_ATTR_RQ_DB : 0;
+
 	return c4iw_modify_qp(rhp, qhp, mask, &attrs, 0);
 }
 
