RDMA/srp: Calculate max_it_iu_size if remote max_it_iu length available

The default maximum immediate size is too big for old srp clients, which
do not support immediate data.

According to the SRP and SRP-2 specifications, the IOControllerProfile
attributes for SRP target ports contains the maximum initiator to target
iu length.

The maximum initiator to target iu length can be obtained by sending MAD
packets to query subnet manager port and SRP target ports. We should
calculate the max_it_iu_size instead of the default value, when remote
maximum initiator to target iu length available.

Link: https://lore.kernel.org/r/20190927174352.7800-2-honli@redhat.com
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Honggang Li <honli@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -1365,7 +1365,8 @@ static void srp_terminate_io(struct srp_rport *rport)
 }
 
 /* Calculate maximum initiator to target information unit length. */
-static uint32_t srp_max_it_iu_len(int cmd_sg_cnt, bool use_imm_data)
+static uint32_t srp_max_it_iu_len(int cmd_sg_cnt, bool use_imm_data,
+				  uint32_t max_it_iu_size)
 {
 	uint32_t max_iu_len = sizeof(struct srp_cmd) + SRP_MAX_ADD_CDB_LEN +
 		sizeof(struct srp_indirect_buf) +
@@ -1375,6 +1376,11 @@ static uint32_t srp_max_it_iu_len(int cmd_sg_cnt, bool use_imm_data)
 		max_iu_len = max(max_iu_len, SRP_IMM_DATA_OFFSET +
 				 srp_max_imm_data);
 
+	if (max_it_iu_size)
+		max_iu_len = min(max_iu_len, max_it_iu_size);
+
+	pr_debug("max_iu_len = %d\n", max_iu_len);
+
 	return max_iu_len;
 }
 
@@ -1392,7 +1398,8 @@ static int srp_rport_reconnect(struct srp_rport *rport)
 	struct srp_target_port *target = rport->lld_data;
 	struct srp_rdma_ch *ch;
 	uint32_t max_iu_len = srp_max_it_iu_len(target->cmd_sg_cnt,
-						srp_use_imm_data);
+						srp_use_imm_data,
+						target->max_it_iu_size);
 	int i, j, ret = 0;
 	bool multich = false;
 
@@ -2541,7 +2548,8 @@ static void srp_cm_rep_handler(struct ib_cm_id *cm_id,
 		ch->req_lim       = be32_to_cpu(lrsp->req_lim_delta);
 		ch->use_imm_data  = lrsp->rsp_flags & SRP_LOGIN_RSP_IMMED_SUPP;
 		ch->max_it_iu_len = srp_max_it_iu_len(target->cmd_sg_cnt,
-						      ch->use_imm_data);
+						      ch->use_imm_data,
+						      target->max_it_iu_size);
 		WARN_ON_ONCE(ch->max_it_iu_len >
 			     be32_to_cpu(lrsp->max_it_iu_len));
 
@@ -3900,7 +3908,9 @@ static ssize_t srp_create_target(struct device *dev,
 	target->mr_per_cmd = mr_per_cmd;
 	target->indirect_size = target->sg_tablesize *
 				sizeof (struct srp_direct_buf);
-	max_iu_len = srp_max_it_iu_len(target->cmd_sg_cnt, srp_use_imm_data);
+	max_iu_len = srp_max_it_iu_len(target->cmd_sg_cnt,
+				       srp_use_imm_data,
+				       target->max_it_iu_size);
 
 	INIT_WORK(&target->tl_err_work, srp_tl_err_work);
 	INIT_WORK(&target->remove_work, srp_remove_work);