staging: fsl-dpaa2/eth: Add Ethernet driver overview document

Add a README file describing the driver architecture, components
and I/O interface.
Signed-off-by: NIoana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fsl-dpaa2/ethernet/README

+Freescale DPAA2 Ethernet driver
+===============================
+
+This file provides documentation for the Freescale DPAA2 Ethernet driver.
+
+
+Contents
+========
+	Supported Platforms
+	Architecture Overview
+	Creating a Network Interface
+	Features & Offloads
+
+
+Supported Platforms
+===================
+This driver provides networking support for Freescale DPAA2 SoCs, e.g.
+LS2080A, LS2088A, LS1088A.
+
+
+Architecture Overview
+=====================
+Unlike regular NICs, in the DPAA2 architecture there is no single hardware block
+representing network interfaces; instead, several separate hardware resources
+concur to provide the networking functionality:
+        - network interfaces
+        - queues, channels
+        - buffer pools
+        - MAC/PHY
+
+All hardware resources are allocated and configured through the Management
+Complex (MC) portals. MC abstracts most of these resources as DPAA2 objects
+and exposes ABIs through which they can be configured and controlled. A few
+hardware resources, like queues, do not have a corresponding MC object and
+are treated as internal resources of other objects.
+
+For a more detailed description of the DPAA2 architecture and its object
+abstractions see:
+	drivers/staging/fsl-mc/README.txt
+
+Each Linux net device is built on top of a Datapath Network Interface (DPNI)
+object and uses Buffer Pools (DPBPs), I/O Portals (DPIOs) and Concentrators
+(DPCONs).
+
+Configuration interface:
+
+                 -----------------------
+                | DPAA2 Ethernet Driver |
+                 -----------------------
+                     .      .      .
+                     .      .      .
+             . . . . .      .      . . . . . .
+             .              .                .
+             .              .                .
+         ----------     ----------      -----------
+        | DPBP API |   | DPNI API |    | DPCON API |
+         ----------     ----------      -----------
+             .              .                .             software
+===========  .  ==========  .  ============  .  ===================
+             .              .                .             hardware
+         ------------------------------------------
+        |            MC hardware portals           |
+         ------------------------------------------
+             .              .                .
+             .              .                .
+          ------         ------            -------
+         | DPBP |       | DPNI |          | DPCON |
+          ------         ------            -------
+
+The DPNIs are network interfaces without a direct one-on-one mapping to PHYs.
+DPBPs represent hardware buffer pools. Packet I/O is performed in the context
+of DPCON objects, using DPIO portals for managing and communicating with the
+hardware resources.
+
+Datapath (I/O) interface:
+
+         -----------------------------------------------
+        |           DPAA2 Ethernet Driver               |
+          -----------------------------------------------
+          |          ^        ^         |            |
+          |          |        |         |            |
+   enqueue|   dequeue|   data |  dequeue|       seed |
+    (Tx)  | (Rx, TxC)|  avail.|  request|     buffers|
+          |          |  notify|         |            |
+          |          |        |         |            |
+          V          |        |         V            V
+         -----------------------------------------------
+        |                 DPIO Driver                   |
+         -----------------------------------------------
+          |          |        |         |            |          software
+          |          |        |         |            |  ================
+          |          |        |         |            |          hardware
+         -----------------------------------------------
+        |               I/O hardware portals            |
+         -----------------------------------------------
+          |          ^        ^         |            |
+          |          |        |         |            |
+          |          |        |         V            |
+          V          |    ================           V
+        ----------------------           |      -------------
+ queues  ----------------------          |     | Buffer pool |
+          ----------------------         |      -------------
+                   =======================
+                                Channel
+
+Datapath I/O (DPIO) portals provide enqueue and dequeue services, data
+availability notifications and buffer pool management. DPIOs are shared between
+all DPAA2 objects (and implicitly all DPAA2 kernel drivers) that work with data
+frames, but must be affine to the CPUs for the purpose of traffic distribution.
+
+Frames are transmitted and received through hardware frame queues, which can be
+grouped in channels for the purpose of hardware scheduling. The Ethernet driver
+enqueues TX frames on egress queues and after transmission is complete a TX
+confirmation frame is sent back to the CPU.
+
+When frames are available on ingress queues, a data availability notification
+is sent to the CPU; notifications are raised per channel, so even if multiple
+queues in the same channel have available frames, only one notification is sent.
+After a channel fires a notification, is must be explicitly rearmed.
+
+Each network interface can have multiple Rx, Tx and confirmation queues affined
+to CPUs, and one channel (DPCON) for each CPU that services at least one queue.
+DPCONs are used to distribute ingress traffic to different CPUs via the cores'
+affine DPIOs.
+
+The role of hardware buffer pools is storage of ingress frame data. Each network
+interface has a privately owned buffer pool which it seeds with kernel allocated
+buffers.
+
+
+DPNIs are decoupled from PHYs; a DPNI can be connected to a PHY through a DPMAC
+object or to another DPNI through an internal link, but the connection is
+managed by MC and completely transparent to the Ethernet driver.
+
+     ---------     ---------     ---------
+    | eth if1 |   | eth if2 |   | eth ifn |
+     ---------     ---------     ---------
+          .           .          .
+          .           .          .
+          .           .          .
+         ---------------------------
+        |   DPAA2 Ethernet Driver   |
+         ---------------------------
+          .           .          .
+          .           .          .
+          .           .          .
+       ------      ------      ------            -------
+      | DPNI |    | DPNI |    | DPNI |          | DPMAC |----+
+       ------      ------      ------            -------     |
+         |           |           |                  |        |
+         |           |           |                  |      -----
+          ===========             ==================      | PHY |
+                                                           -----
+
+Creating a Network Interface
+============================
+A net device is created for each DPNI object probed on the MC bus. Each DPNI has
+a number of properties which determine the network interface configuration
+options and associated hardware resources.
+
+DPNI objects (and the other DPAA2 objects needed for a network interface) can be
+added to a container on the MC bus in one of two ways: statically, through a
+Datapath Layout Binary file (DPL) that is parsed by MC at boot time; or created
+dynamically at runtime, via the DPAA2 objects APIs.
+
+
+Features & Offloads
+===================
+Hardware checksum offloading is supported for TCP and UDP over IPv4/6 frames.
+The checksum offloads can be independently configured on RX and TX through
+ethtool.
+
+Hardware offload of unicast and multicast MAC filtering is supported on the
+ingress path and permanently enabled.
+
+Scatter-gather frames are supported on both RX and TX paths. On TX, SG support
+is configurable via ethtool; on RX it is always enabled.
+
+The DPAA2 hardware can process jumbo Ethernet frames of up to 10K bytes.
+
+The Ethernet driver defines a static flow hashing scheme that distributes
+traffic based on a 5-tuple key: src IP, dst IP, IP proto, L4 src port,
+L4 dst port. No user configuration is supported for now.
+
+Hardware specific statistics for the network interface as well as some
+non-standard driver stats can be consulted through ethtool -S option.