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diff --git a/Documentation/scsi/cxgb3i.rst b/Documentation/scsi/cxgb3i.rst new file mode 100644 index 000000000000..e01f18fbfa9f --- /dev/null +++ b/Documentation/scsi/cxgb3i.rst @@ -0,0 +1,90 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================= +Chelsio S3 iSCSI Driver for Linux +================================= + +Introduction +============ + +The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc. +series of products) support iSCSI acceleration and iSCSI Direct Data Placement +(DDP) where the hardware handles the expensive byte touching operations, such +as CRC computation and verification, and direct DMA to the final host memory +destination: + + - iSCSI PDU digest generation and verification + + On transmitting, Chelsio S3 h/w computes and inserts the Header and + Data digest into the PDUs. + On receiving, Chelsio S3 h/w computes and verifies the Header and + Data digest of the PDUs. + + - Direct Data Placement (DDP) + + S3 h/w can directly place the iSCSI Data-In or Data-Out PDU's + payload into pre-posted final destination host-memory buffers based + on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT) + in Data-Out PDUs. + + - PDU Transmit and Recovery + + On transmitting, S3 h/w accepts the complete PDU (header + data) + from the host driver, computes and inserts the digests, decomposes + the PDU into multiple TCP segments if necessary, and transmit all + the TCP segments onto the wire. It handles TCP retransmission if + needed. + + On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP + segments, separating the header and data, calculating and verifying + the digests, then forwarding the header to the host. The payload data, + if possible, will be directly placed into the pre-posted host DDP + buffer. Otherwise, the payload data will be sent to the host too. + +The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI +acceleration through Chelsio hardware wherever applicable. + +Using the cxgb3i Driver +======================= + +The following steps need to be taken to accelerates the open-iscsi initiator: + +1. Load the cxgb3i driver: "modprobe cxgb3i" + + The cxgb3i module registers a new transport class "cxgb3i" with open-iscsi. + + * in the case of recompiling the kernel, the cxgb3i selection is located at:: + + Device Drivers + SCSI device support ---> + [*] SCSI low-level drivers ---> + <M> Chelsio S3xx iSCSI support + +2. Create an interface file located under /etc/iscsi/ifaces/ for the new + transport class "cxgb3i". + + The content of the file should be in the following format:: + + iface.transport_name = cxgb3i + iface.net_ifacename = <ethX> + iface.ipaddress = <iscsi ip address> + + * if iface.ipaddress is specified, <iscsi ip address> needs to be either the + same as the ethX's ip address or an address on the same subnet. Make + sure the ip address is unique in the network. + +3. edit /etc/iscsi/iscsid.conf + The default setting for MaxRecvDataSegmentLength (131072) is too big; + replace with a value no bigger than 15360 (for example 8192):: + + node.conn[0].iscsi.MaxRecvDataSegmentLength = 8192 + + * The login would fail for a normal session if MaxRecvDataSegmentLength is + too big. A error message in the format of + "cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>." + would be logged to dmesg. + +4. To direct open-iscsi traffic to go through cxgb3i's accelerated path, + "-I <iface file name>" option needs to be specified with most of the + iscsiadm command. <iface file name> is the transport interface file created + in step 2. |