linux_kernel/Documentation/networking/dpaa2/overview.rst

.. include:: <isonum.txt>

=========================================================
DPAA2 (Data Path Acceleration Architecture Gen2) Overview
=========================================================

:Copyright: |copy| 2015 Freescale Semiconductor Inc.
:Copyright: |copy| 2018 NXP

This document provides an overview of the Freescale DPAA2 architecture
and how it is integrated into the Linux kernel.

Introduction
============

DPAA2 is a hardware architecture designed for high-speeed network
packet processing.  DPAA2 consists of sophisticated mechanisms for
processing Ethernet packets, queue management, buffer management,
autonomous L2 switching, virtual Ethernet bridging, and accelerator
(e.g. crypto) sharing.

A DPAA2 hardware component called the Management Complex (or MC) manages the
DPAA2 hardware resources.  The MC provides an object-based abstraction for
software drivers to use the DPAA2 hardware.
The MC uses DPAA2 hardware resources such as queues, buffer pools, and
network ports to create functional objects/devices such as network
interfaces, an L2 switch, or accelerator instances.
The MC provides memory-mapped I/O command interfaces (MC portals)
which DPAA2 software drivers use to operate on DPAA2 objects.

The diagram below shows an overview of the DPAA2 resource management
architecture::

	+--------------------------------------+
	|                  OS                  |
	|                        DPAA2 drivers |
	|                             |        |
	+-----------------------------|--------+
	                              |
	                              | (create,discover,connect
	                              |  config,use,destroy)
	                              |
	                 DPAA2        |
	+------------------------| mc portal |-+
	|                             |        |
	|   +- - - - - - - - - - - - -V- - -+  |
	|   |                               |  |
	|   |   Management Complex (MC)     |  |
	|   |                               |  |
	|   +- - - - - - - - - - - - - - - -+  |
	|                                      |
	| Hardware                  Hardware   |
	| Resources                 Objects    |
	| ---------                 -------    |
	| -queues                   -DPRC      |
	| -buffer pools             -DPMCP     |
	| -Eth MACs/ports           -DPIO      |
	| -network interface        -DPNI      |
	|  profiles                 -DPMAC     |
	| -queue portals            -DPBP      |
	| -MC portals                ...       |
	|  ...                                 |
	|                                      |
	+--------------------------------------+


The MC mediates operations such as create, discover,
connect, configuration, and destroy.  Fast-path operations
on data, such as packet transmit/receive, are not mediated by
the MC and are done directly using memory mapped regions in
DPIO objects.

Overview of DPAA2 Objects
=========================

The section provides a brief overview of some key DPAA2 objects.
A simple scenario is described illustrating the objects involved
in creating a network interfaces.

DPRC (Datapath Resource Container)
----------------------------------

A DPRC is a container object that holds all the other
types of DPAA2 objects.  In the example diagram below there
are 8 objects of 5 types (DPMCP, DPIO, DPBP, DPNI, and DPMAC)
in the container.

::

	+---------------------------------------------------------+
	| DPRC                                                    |
	|                                                         |
	|  +-------+  +-------+  +-------+  +-------+  +-------+  |
	|  | DPMCP |  | DPIO  |  | DPBP  |  | DPNI  |  | DPMAC |  |
	|  +-------+  +-------+  +-------+  +---+---+  +---+---+  |
	|  | DPMCP |  | DPIO  |                                   |
	|  +-------+  +-------+                                   |
	|  | DPMCP |                                              |
	|  +-------+                                              |
	|                                                         |
	+---------------------------------------------------------+

From the point of view of an OS, a DPRC behaves similar to a plug and
play bus, like PCI.  DPRC commands can be used to enumerate the contents
of the DPRC, discover the hardware objects present (including mappable
regions and interrupts).

::

	DPRC.1 (bus)
	   |
	   +--+--------+-------+-------+-------+
	      |        |       |       |       |
	    DPMCP.1  DPIO.1  DPBP.1  DPNI.1  DPMAC.1
	    DPMCP.2  DPIO.2
	    DPMCP.3

Hardware objects can be created and destroyed dynamically, providing
the ability to hot plug/unplug objects in and out of the DPRC.

A DPRC has a mappable MMIO region (an MC portal) that can be used
to send MC commands.  It has an interrupt for status events (like
hotplug).
All objects in a container share the same hardware "isolation context".
This means that with respect to an IOMMU the isolation granularity
is at the DPRC (container) level, not at the individual object
level.

DPRCs can be defined statically and populated with objects
via a config file passed to the MC when firmware starts it.

DPAA2 Objects for an Ethernet Network Interface
-----------------------------------------------

A typical Ethernet NIC is monolithic-- the NIC device contains TX/RX
queuing mechanisms, configuration mechanisms, buffer management,
physical ports, and interrupts.  DPAA2 uses a more granular approach
utilizing multiple hardware objects.  Each object provides specialized
functions. Groups of these objects are used by software to provide
Ethernet network interface functionality.  This approach provides
efficient use of finite hardware resources, flexibility, and
performance advantages.

The diagram below shows the objects needed for a simple
network interface configuration on a system with 2 CPUs.

::

	+---+---+ +---+---+
	   CPU0     CPU1
	+---+---+ +---+---+
	    |         |
	+---+---+ +---+---+
	   DPIO     DPIO
	+---+---+ +---+---+
	    \     /
	     \   /
	      \ /
	   +---+---+
	      DPNI  --- DPBP,DPMCP
	   +---+---+
	       |
	       |
	   +---+---+
	     DPMAC
	   +---+---+
	       |
	   port/PHY

Below the objects are described.  For each object a brief description
is provided along with a summary of the kinds of operations the object
supports and a summary of key resources of the object (MMIO regions
and IRQs).

DPMAC (Datapath Ethernet MAC)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Represents an Ethernet MAC, a hardware device that connects to an Ethernet
PHY and allows physical transmission and reception of Ethernet frames.

- MMIO regions: none
- IRQs: DPNI link change
- commands: set link up/down, link config, get stats,
  IRQ config, enable, reset

DPNI (Datapath Network Interface)
Contains TX/RX queues, network interface configuration, and RX buffer pool
configuration mechanisms.  The TX/RX queues are in memory and are identified
by queue number.

- MMIO regions: none
- IRQs: link state
- commands: port config, offload config, queue config,
  parse/classify config, IRQ config, enable, reset

DPIO (Datapath I/O)
~~~~~~~~~~~~~~~~~~~
Provides interfaces to enqueue and dequeue
packets and do hardware buffer pool management operations.  The DPAA2
architecture separates the mechanism to access queues (the DPIO object)
from the queues themselves.  The DPIO provides an MMIO interface to
enqueue/dequeue packets.  To enqueue something a descriptor is written
to the DPIO MMIO region, which includes the target queue number.
There will typically be one DPIO assigned to each CPU.  This allows all
CPUs to simultaneously perform enqueue/dequeued operations.  DPIOs are
expected to be shared by different DPAA2 drivers.

- MMIO regions: queue operations, buffer management
- IRQs: data availability, congestion notification, buffer
  pool depletion
- commands: IRQ config, enable, reset

DPBP (Datapath Buffer Pool)
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Represents a hardware buffer pool.

- MMIO regions: none
- IRQs: none
- commands: enable, reset

DPMCP (Datapath MC Portal)
~~~~~~~~~~~~~~~~~~~~~~~~~~
Provides an MC command portal.
Used by drivers to send commands to the MC to manage
objects.

- MMIO regions: MC command portal
- IRQs: command completion
- commands: IRQ config, enable, reset

Object Connections
==================
Some objects have explicit relationships that must
be configured:

- DPNI <--> DPMAC
- DPNI <--> DPNI
- DPNI <--> L2-switch-port

    A DPNI must be connected to something such as a DPMAC,
    another DPNI, or L2 switch port.  The DPNI connection
    is made via a DPRC command.

::

              +-------+  +-------+
              | DPNI  |  | DPMAC |
              +---+---+  +---+---+
                  |          |
                  +==========+

- DPNI <--> DPBP

    A network interface requires a 'buffer pool' (DPBP
    object) which provides a list of pointers to memory
    where received Ethernet data is to be copied.  The
    Ethernet driver configures the DPBPs associated with
    the network interface.

Interrupts
==========
All interrupts generated by DPAA2 objects are message
interrupts.  At the hardware level message interrupts
generated by devices will normally have 3 components--
1) a non-spoofable 'device-id' expressed on the hardware
bus, 2) an address, 3) a data value.

In the case of DPAA2 devices/objects, all objects in the
same container/DPRC share the same 'device-id'.
For ARM-based SoC this is the same as the stream ID.


DPAA2 Linux Drivers Overview
============================

This section provides an overview of the Linux kernel drivers for
DPAA2-- 1) the bus driver and associated "DPAA2 infrastructure"
drivers and 2) functional object drivers (such as Ethernet).

As described previously, a DPRC is a container that holds the other
types of DPAA2 objects.  It is functionally similar to a plug-and-play
bus controller.
Each object in the DPRC is a Linux "device" and is bound to a driver.
The diagram below shows the Linux drivers involved in a networking
scenario and the objects bound to each driver.  A brief description
of each driver follows.

::

	                                     +------------+
	                                     | OS Network |
	                                     |   Stack    |
	         +------------+              +------------+
	         | Allocator  |. . . . . . . |  Ethernet  |
	         |(DPMCP,DPBP)|              |   (DPNI)   |
	         +-.----------+              +---+---+----+
	          .          .                   ^   |
	         .            .     <data avail, |   | <enqueue,
	        .              .     tx confirm> |   | dequeue>
	+-------------+         .                |   |
	| DPRC driver |          .           +---+---V----+     +---------+
	|   (DPRC)    |           . . . . . .| DPIO driver|     |   MAC   |
	+----------+--+                      |  (DPIO)    |     | (DPMAC) |
	           |                         +------+-----+     +-----+---+
	           |<dev add/remove>                |                 |
	           |                                |                 |
	  +--------+----------+                     |              +--+---+
	  |   MC-bus driver   |                     |              | PHY  |
	  |                   |                     |              |driver|
	  |   /bus/fsl-mc     |                     |              +--+---+
	  +-------------------+                     |                 |
	                                            |                 |
	========================= HARDWARE =========|=================|======
	                                          DPIO                |
	                                            |                 |
	                                          DPNI---DPBP         |
	                                            |                 |
	                                          DPMAC               |
	                                            |                 |
	                                           PHY ---------------+
	============================================|========================

A brief description of each driver is provided below.

MC-bus driver
-------------
The MC-bus driver is a platform driver and is probed from a
node in the device tree (compatible "fsl,qoriq-mc") passed in by boot
firmware.  It is responsible for bootstrapping the DPAA2 kernel
infrastructure.
Key functions include:

- registering a new bus type named "fsl-mc" with the kernel,
  and implementing bus call-backs (e.g. match/uevent/dev_groups)
- implementing APIs for DPAA2 driver registration and for device
  add/remove
- creates an MSI IRQ domain
- doing a 'device add' to expose the 'root' DPRC, in turn triggering
  a bind of the root DPRC to the DPRC driver

The binding for the MC-bus device-tree node can be consulted at
*Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt*.
The sysfs bind/unbind interfaces for the MC-bus can be consulted at
*Documentation/ABI/testing/sysfs-bus-fsl-mc*.

DPRC driver
-----------
The DPRC driver is bound to DPRC objects and does runtime management
of a bus instance.  It performs the initial bus scan of the DPRC
and handles interrupts for container events such as hot plug by
re-scanning the DPRC.

Allocator
---------
Certain objects such as DPMCP and DPBP are generic and fungible,
and are intended to be used by other drivers.  For example,
the DPAA2 Ethernet driver needs:

- DPMCPs to send MC commands, to configure network interfaces
- DPBPs for network buffer pools

The allocator driver registers for these allocatable object types
and those objects are bound to the allocator when the bus is probed.
The allocator maintains a pool of objects that are available for
allocation by other DPAA2 drivers.

DPIO driver
-----------
The DPIO driver is bound to DPIO objects and provides services that allow
other drivers such as the Ethernet driver to enqueue and dequeue data for
their respective objects.
Key services include:

- data availability notifications
- hardware queuing operations (enqueue and dequeue of data)
- hardware buffer pool management

To transmit a packet the Ethernet driver puts data on a queue and
invokes a DPIO API.  For receive, the Ethernet driver registers
a data availability notification callback.  To dequeue a packet
a DPIO API is used.
There is typically one DPIO object per physical CPU for optimum
performance, allowing different CPUs to simultaneously enqueue
and dequeue data.

The DPIO driver operates on behalf of all DPAA2 drivers
active in the kernel--  Ethernet, crypto, compression,
etc.

Ethernet driver
---------------
The Ethernet driver is bound to a DPNI and implements the kernel
interfaces needed to connect the DPAA2 network interface to
the network stack.
Each DPNI corresponds to a Linux network interface.

MAC driver
----------
An Ethernet PHY is an off-chip, board specific component and is managed
by the appropriate PHY driver via an mdio bus.  The MAC driver
plays a role of being a proxy between the PHY driver and the
MC.  It does this proxy via the MC commands to a DPMAC object.
If the PHY driver signals a link change, the MAC driver notifies
the MC via a DPMAC command.  If a network interface is brought
up or down, the MC notifies the DPMAC driver via an interrupt and
the driver can take appropriate action.