IB/opa-vnic: Virtual Network Interface Controller (VNIC) documentation

Add OPA VNIC design document explaining the VNIC architecture and the
driver design.
Reviewed-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: NIra Weiny <ira.weiny@intel.com>
Signed-off-by: NNiranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

Documentation/infiniband/opa_vnic.txt

+Intel Omni-Path (OPA) Virtual Network Interface Controller (VNIC) feature
+supports Ethernet functionality over Omni-Path fabric by encapsulating
+the Ethernet packets between HFI nodes.
+
+Architecture
+=============
+The patterns of exchanges of Omni-Path encapsulated Ethernet packets
+involves one or more virtual Ethernet switches overlaid on the Omni-Path
+fabric topology. A subset of HFI nodes on the Omni-Path fabric are
+permitted to exchange encapsulated Ethernet packets across a particular
+virtual Ethernet switch. The virtual Ethernet switches are logical
+abstractions achieved by configuring the HFI nodes on the fabric for
+header generation and processing. In the simplest configuration all HFI
+nodes across the fabric exchange encapsulated Ethernet packets over a
+single virtual Ethernet switch. A virtual Ethernet switch, is effectively
+an independent Ethernet network. The configuration is performed by an
+Ethernet Manager (EM) which is part of the trusted Fabric Manager (FM)
+application. HFI nodes can have multiple VNICs each connected to a
+different virtual Ethernet switch. The below diagram presents a case
+of two virtual Ethernet switches with two HFI nodes.
+
+                             +-------------------+
+                             |      Subnet/      |
+                             |     Ethernet      |
+                             |      Manager      |
+                             +-------------------+
+                                /          /
+                              /           /
+                            /            /
+                          /             /
++-----------------------------+  +------------------------------+
+|  Virtual Ethernet Switch    |  |  Virtual Ethernet Switch     |
+|  +---------+    +---------+ |  | +---------+    +---------+   |
+|  | VPORT   |    |  VPORT  | |  | |  VPORT  |    |  VPORT  |   |
++--+---------+----+---------+-+  +-+---------+----+---------+---+
+         |                 \        /                 |
+         |                   \    /                   |
+         |                     \/                     |
+         |                    /  \                    |
+         |                  /      \                  |
+     +-----------+------------+  +-----------+------------+
+     |   VNIC    |    VNIC    |  |    VNIC   |    VNIC    |
+     +-----------+------------+  +-----------+------------+
+     |          HFI           |  |          HFI           |
+     +------------------------+  +------------------------+
+
+
+The Omni-Path encapsulated Ethernet packet format is as described below.
+
+Bits          Field
+------------------------------------
+Quad Word 0:
+0-19      SLID (lower 20 bits)
+20-30     Length (in Quad Words)
+31        BECN bit
+32-51     DLID (lower 20 bits)
+52-56     SC (Service Class)
+57-59     RC (Routing Control)
+60        FECN bit
+61-62     L2 (=10, 16B format)
+63        LT (=1, Link Transfer Head Flit)
+
+Quad Word 1:
+0-7       L4 type (=0x78 ETHERNET)
+8-11      SLID[23:20]
+12-15     DLID[23:20]
+16-31     PKEY
+32-47     Entropy
+48-63     Reserved
+
+Quad Word 2:
+0-15      Reserved
+16-31     L4 header
+32-63     Ethernet Packet
+
+Quad Words 3 to N-1:
+0-63      Ethernet packet (pad extended)
+
+Quad Word N (last):
+0-23      Ethernet packet (pad extended)
+24-55     ICRC
+56-61     Tail
+62-63     LT (=01, Link Transfer Tail Flit)
+
+Ethernet packet is padded on the transmit side to ensure that the VNIC OPA
+packet is quad word aligned. The 'Tail' field contains the number of bytes
+padded. On the receive side the 'Tail' field is read and the padding is
+removed (along with ICRC, Tail and OPA header) before passing packet up
+the network stack.
+
+The L4 header field contains the virtual Ethernet switch id the VNIC port
+belongs to. On the receive side, this field is used to de-multiplex the
+received VNIC packets to different VNIC ports.
+
+Driver Design
+==============
+Intel OPA VNIC software design is presented in the below diagram.
+OPA VNIC functionality has a HW dependent component and a HW
+independent component.
+
+The support has been added for IB device to allocate and free the RDMA
+netdev devices. The RDMA netdev supports interfacing with the network
+stack thus creating standard network interfaces. OPA_VNIC is an RDMA
+netdev device type.
+
+The HW dependent VNIC functionality is part of the HFI1 driver. It
+implements the verbs to allocate and free the OPA_VNIC RDMA netdev.
+It involves HW resource allocation/management for VNIC functionality.
+It interfaces with the network stack and implements the required
+net_device_ops functions. It expects Omni-Path encapsulated Ethernet
+packets in the transmit path and provides HW access to them. It strips
+the Omni-Path header from the received packets before passing them up
+the network stack. It also implements the RDMA netdev control operations.
+
+The OPA VNIC module implements the HW independent VNIC functionality.
+It consists of two parts. The VNIC Ethernet Management Agent (VEMA)
+registers itself with IB core as an IB client and interfaces with the
+IB MAD stack. It exchanges the management information with the Ethernet
+Manager (EM) and the VNIC netdev. The VNIC netdev part allocates and frees
+the OPA_VNIC RDMA netdev devices. It overrides the net_device_ops functions
+set by HW dependent VNIC driver where required to accommodate any control
+operation. It also handles the encapsulation of Ethernet packets with an
+Omni-Path header in the transmit path. For each VNIC interface, the
+information required for encapsulation is configured by the EM via VEMA MAD
+interface. It also passes any control information to the HW dependent driver
+by invoking the RDMA netdev control operations.
+
+        +-------------------+ +----------------------+
+        |                   | |       Linux          |
+        |     IB MAD        | |      Network         |
+        |                   | |       Stack          |
+        +-------------------+ +----------------------+
+                 |               |          |
+                 |               |          |
+        +----------------------------+      |
+        |                            |      |
+        |      OPA VNIC Module       |      |
+        |  (OPA VNIC RDMA Netdev     |      |
+        |     & EMA functions)       |      |
+        |                            |      |
+        +----------------------------+      |
+                    |                       |
+                    |                       |
+           +------------------+             |
+           |     IB core      |             |
+           +------------------+             |
+                    |                       |
+                    |                       |
+        +--------------------------------------------+
+        |                                            |
+        |      HFI1 Driver with VNIC support         |
+        |                                            |
+        +--------------------------------------------+