IB/cma: Introduce rdma_set_min_rnr_timer()

Introduce the ability for kernel ULPs to adjust the minimum RNR Retry
timer. The INIT -> RTR transition executed by RDMA CM will be used for
this adjustment. This avoids an additional ib_modify_qp() call.

rdma_set_min_rnr_timer() must be called before the call to rdma_connect()
on the active side and before the call to rdma_accept() on the passive
side.

The default value of RNR Retry timer is zero, which translates to 655
ms. When the receiver is not ready to accept a send messages, it encodes
the RNR Retry timer value in the NAK. The requestor will then wait at
least the specified time value before retrying the send.

The 5-bit value to be supplied to the rdma_set_min_rnr_timer() is
documented in IBTA Table 45: "Encoding for RNR NAK Timer Field".

Link: https://lore.kernel.org/r/1617216194-12890-2-git-send-email-haakon.bugge@oracle.comSigned-off-by: NHåkon Bugge <haakon.bugge@oracle.com>
Acked-by: NJason Gunthorpe <jgg@nvidia.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/cma.c

@@ -843,6 +843,7 @@ __rdma_create_id(struct net *net, rdma_cm_event_handler event_handler,
 	id_priv->id.qp_type = qp_type;
 	id_priv->tos_set = false;
 	id_priv->timeout_set = false;
+	id_priv->min_rnr_timer_set = false;
 	id_priv->gid_type = IB_GID_TYPE_IB;
 	spin_lock_init(&id_priv->lock);
 	mutex_init(&id_priv->qp_mutex);
@@ -1133,6 +1134,9 @@ int rdma_init_qp_attr(struct rdma_cm_id *id, struct ib_qp_attr *qp_attr,
 	if ((*qp_attr_mask & IB_QP_TIMEOUT) && id_priv->timeout_set)
 		qp_attr->timeout = id_priv->timeout;
 
+	if ((*qp_attr_mask & IB_QP_MIN_RNR_TIMER) && id_priv->min_rnr_timer_set)
+		qp_attr->min_rnr_timer = id_priv->min_rnr_timer;
+
 	return ret;
 }
 EXPORT_SYMBOL(rdma_init_qp_attr);
@@ -2608,6 +2612,43 @@ int rdma_set_ack_timeout(struct rdma_cm_id *id, u8 timeout)
 }
 EXPORT_SYMBOL(rdma_set_ack_timeout);
 
+/**
+ * rdma_set_min_rnr_timer() - Set the minimum RNR Retry timer of the
+ *			      QP associated with a connection identifier.
+ * @id: Communication identifier to associated with service type.
+ * @min_rnr_timer: 5-bit value encoded as Table 45: "Encoding for RNR NAK
+ *		   Timer Field" in the IBTA specification.
+ *
+ * This function should be called before rdma_connect() on active
+ * side, and on passive side before rdma_accept(). The timer value
+ * will be associated with the local QP. When it receives a send it is
+ * not read to handle, typically if the receive queue is empty, an RNR
+ * Retry NAK is returned to the requester with the min_rnr_timer
+ * encoded. The requester will then wait at least the time specified
+ * in the NAK before retrying. The default is zero, which translates
+ * to a minimum RNR Timer value of 655 ms.
+ *
+ * Return: 0 for success
+ */
+int rdma_set_min_rnr_timer(struct rdma_cm_id *id, u8 min_rnr_timer)
+{
+	struct rdma_id_private *id_priv;
+
+	/* It is a five-bit value */
+	if (min_rnr_timer & 0xe0)
+		return -EINVAL;
+
+	if (WARN_ON(id->qp_type != IB_QPT_RC && id->qp_type != IB_QPT_XRC_TGT))
+		return -EINVAL;
+
+	id_priv = container_of(id, struct rdma_id_private, id);
+	id_priv->min_rnr_timer = min_rnr_timer;
+	id_priv->min_rnr_timer_set = true;
+
+	return 0;
+}
+EXPORT_SYMBOL(rdma_set_min_rnr_timer);
+
 static void cma_query_handler(int status, struct sa_path_rec *path_rec,
 			      void *context)
 {

drivers/infiniband/core/cma_priv.h

@@ -86,9 +86,11 @@ struct rdma_id_private {
 	u8			tos;
 	u8			tos_set:1;
 	u8                      timeout_set:1;
+	u8			min_rnr_timer_set:1;
 	u8			reuseaddr;
 	u8			afonly;
 	u8			timeout;
+	u8			min_rnr_timer;
 	enum ib_gid_type	gid_type;
 
 	/*

include/rdma/rdma_cm.h

@@ -331,6 +331,8 @@ int rdma_set_reuseaddr(struct rdma_cm_id *id, int reuse);
 int rdma_set_afonly(struct rdma_cm_id *id, int afonly);
 
 int rdma_set_ack_timeout(struct rdma_cm_id *id, u8 timeout);
+
+int rdma_set_min_rnr_timer(struct rdma_cm_id *id, u8 min_rnr_timer);
  /**
  * rdma_get_service_id - Return the IB service ID for a specified address.
  * @id: Communication identifier associated with the address.