[PATCH RFC v2] Documentation/infiniband: Add docs for rdma-helpers

[Michael Wang <yun.wang@profitbricks.com>]

Since v1:
  * Merge the descriptions from Doug:
    http://www.spinics.net/lists/linux-rdma/msg25172.html

This is the following patch for:
  https://lkml.org/lkml/2015/5/5/417
which try to document the settled rdma_cap_XX().

Highlights:
  There could be many missing/mistakes/misunderstanding, please don't
  be hesitate to point out the issues, any suggestions to improve or
  complete the description are very welcomed ;-)

Signed-off-by: Michael Wang <yun.wang@profitbricks.com>
---
 Documentation/infiniband/rdma_helpers.txt | 79 +++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 Documentation/infiniband/rdma_helpers.txt

diff --git a/Documentation/infiniband/rdma_helpers.txt b/Documentation/infiniband/rdma_helpers.txt
new file mode 100644
index 0000000..be9416d
--- /dev/null
+++ b/Documentation/infiniband/rdma_helpers.txt
@@ -0,0 +1,79 @@
+RDMA HELPERS
+
+  The following helpers are used to check the specific capabilities of a
+  particular port before utilizing those capabilities.
+
+    rdma_cap_ib_mad		- Infiniband Management Datagrams.
+    rdma_cap_ib_smi		- Infiniband Subnet Management Interface.
+    rdma_cap_ib_cm		- Infiniband Communication Manager.
+    rdma_cap_iw_cm		- IWARP Communication Manager.
+    rdma_cap_ib_sa		- Infiniband Subnet Administration.
+    rdma_cap_ib_mcast		- Infiniband Multicast Join/Leave Protocol.
+    rdma_cap_read_multi_sge	- RDMA Read Work Request Support Multiple SGE.
+    rdma_cap_af_ib		- Native Infiniband Address.
+    rdma_cap_eth_ah		- InfiniBand Transport With Ethernet Address.
+
+USAGE
+
+  if (rdma_cap_XX(device, i)) {
+	/* The port i of device support XX */
+	...
+  } else {
+	/* The port i of device don't support XX */
+	...
+  }
+
+  rdma_cap_ib_mad
+  ---------------
+    Management Datagrams (MAD) are a required part of the InfiniBand
+    specification and are supported on all InfiniBand devices.  A slightly
+    extended version are also supported on OPA interfaces.
+
+  rdma_cap_ib_smi
+  ---------------
+    Subnet Management Interface (SMI) will handle SMP packet from SM
+    in an infiniband fabric.
+
+  rdma_cap_ib_cm
+  ---------------
+    Communication Manager (CM) service, used to ease the process of connecting
+    to a remote host.  The IB-CM can be used to connect to remote hosts using
+    either InfiniBand or RoCE connections, iWARP has its own CM.
+
+  rdma_cap_iw_cm
+  ---------------
+    iWARP Communication Manager (CM), Similar to the IB-CM, but only used on
+    iWARP devices.
+
+  rdma_cap_ib_sa
+  ---------------
+    Subnet Administration (SA) is the database built by SM in an
+    infiniband fabric.
+
+  rdma_cap_ib_mcast
+  ---------------
+    InfiniBand (and OPA) use a different multicast mechanism rather than
+    traditional IP multicast found on Ethernet devices.  If this is true, then
+    traditional IPv4/IPv6 multicast is handled by the IPoIB layer and direct
+    multicast joins and leaves are handled per the InfiniBand specifications.
+
+  rdma_cap_read_multi_sge
+  ---------------
+    Certain devices (iWARP in particular) have restrictions on the number of
+    scatter gather elements that can be present in an RDMA READ work request,
+    this is true if the device does not have that restriction.
+
+  rdma_cap_af_ib
+  ---------------
+    Many code paths for traditional InfiniBand and RoCE links are the same,
+    but need minor differences to accommodate the different addresses on the
+    two types of connections.  This helper is true when the address of the
+    specific connection is of the InfiniBand native variety.
+
+  rdma_cap_eth_ah
+  ---------------
+    Queue Pair is InfiniBand transport, but uses Ethernet address instead
+    of native InfiniBand address (aka, this is a RoCE QP, and that means
+    ethertype 0x8915 + GRH for RoCEv1 and IP/UDP to well known UDP port for
+    RoCEv2), this is true when the address family of the specific queue pair
+    is of the Ethernet (RoCE) variety.
-- 
2.1.0