xref: /openbmc/linux/Documentation/networking/device_drivers/ethernet/freescale/dpaa2/ethernet-driver.rst (revision 132db935)

.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

===============================
DPAA2 Ethernet driver
===============================

:Copyright: |copy| 2017-2018 NXP

This file provides documentation for the Freescale DPAA2 Ethernet driver.

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
*Documentation/networking/device_drivers/ethernet/freescale/dpaa2/overview.rst*.

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.