[SCSI] cxgb3i: Add cxgb3i iSCSI driver.

This patch implements the cxgb3i iscsi connection acceleration for the
open-iscsi initiator.

The cxgb3i driver offers the iscsi PDU based offload:
- digest insertion and verification
- payload direct-placement into host memory buffer.

Signed-off-by: Karen Xie <kxie@chelsio.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/Documentation/scsi/cxgb3i.txt b/Documentation/scsi/cxgb3i.txt
new file mode 100644
index 000000000000..8141fa01978e
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+++ b/Documentation/scsi/cxgb3i.txt
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+Chelsio S3 iSCSI Driver for Linux
+
+Introduction
+============
+
+The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc.
+series of products) supports 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 receving, S3 h/w recovers the iSCSI PDU by reassembling TCP
+          segments, separating the header and data, calculating and verifying
+          the digests, then forwards 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 "node.conn[0].iscsi.MaxRecvDataSegmentLength" to be 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.