1.. SPDX-License-Identifier: GPL-2.0
2
3=================================
4Chelsio S3 iSCSI Driver for Linux
5=================================
6
7Introduction
8============
9
10The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc.
11series of products) support iSCSI acceleration and iSCSI Direct Data Placement
12(DDP) where the hardware handles the expensive byte touching operations, such
13as CRC computation and verification, and direct DMA to the final host memory
14destination:
15
16	- iSCSI PDU digest generation and verification
17
18	  On transmitting, Chelsio S3 h/w computes and inserts the Header and
19	  Data digest into the PDUs.
20	  On receiving, Chelsio S3 h/w computes and verifies the Header and
21	  Data digest of the PDUs.
22
23	- Direct Data Placement (DDP)
24
25	  S3 h/w can directly place the iSCSI Data-In or Data-Out PDU's
26	  payload into pre-posted final destination host-memory buffers based
27	  on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT)
28	  in Data-Out PDUs.
29
30	- PDU Transmit and Recovery
31
32	  On transmitting, S3 h/w accepts the complete PDU (header + data)
33	  from the host driver, computes and inserts the digests, decomposes
34	  the PDU into multiple TCP segments if necessary, and transmit all
35	  the TCP segments onto the wire. It handles TCP retransmission if
36	  needed.
37
38	  On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP
39	  segments, separating the header and data, calculating and verifying
40	  the digests, then forwarding the header to the host. The payload data,
41	  if possible, will be directly placed into the pre-posted host DDP
42	  buffer. Otherwise, the payload data will be sent to the host too.
43
44The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI
45acceleration through Chelsio hardware wherever applicable.
46
47Using the cxgb3i Driver
48=======================
49
50The following steps need to be taken to accelerates the open-iscsi initiator:
51
521. Load the cxgb3i driver: "modprobe cxgb3i"
53
54   The cxgb3i module registers a new transport class "cxgb3i" with open-iscsi.
55
56   * in the case of recompiling the kernel, the cxgb3i selection is located at::
57
58	Device Drivers
59		SCSI device support --->
60			[*] SCSI low-level drivers  --->
61				<M>   Chelsio S3xx iSCSI support
62
632. Create an interface file located under /etc/iscsi/ifaces/ for the new
64   transport class "cxgb3i".
65
66   The content of the file should be in the following format::
67
68	iface.transport_name = cxgb3i
69	iface.net_ifacename = <ethX>
70	iface.ipaddress = <iscsi ip address>
71
72   * if iface.ipaddress is specified, <iscsi ip address> needs to be either the
73     same as the ethX's ip address or an address on the same subnet. Make
74     sure the ip address is unique in the network.
75
763. edit /etc/iscsi/iscsid.conf
77   The default setting for MaxRecvDataSegmentLength (131072) is too big;
78   replace with a value no bigger than 15360 (for example 8192)::
79
80	node.conn[0].iscsi.MaxRecvDataSegmentLength = 8192
81
82   * The login would fail for a normal session if MaxRecvDataSegmentLength is
83     too big.  A error message in the format of
84     "cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>."
85     would be logged to dmesg.
86
874. To direct open-iscsi traffic to go through cxgb3i's accelerated path,
88   "-I <iface file name>" option needs to be specified with most of the
89   iscsiadm command. <iface file name> is the transport interface file created
90   in step 2.
91