staging: fsl-mc: add DPAA2 overview readme
add README file providing an overview of the DPAA2 architecture and how it is integrated in Linux Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Stuart Yoder
Greg Kroah-Hartman
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Copyright (C) 2015 Freescale Semiconductor Inc.
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DPAA2 (Data Path Acceleration Architecture Gen2)
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------------------------------------------------
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This document provides an overview of the Freescale DPAA2 architecture
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and how it is integrated into the Linux kernel.
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Contents summary
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-DPAA2 overview
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-Overview of DPAA2 objects
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-DPAA2 Linux driver architecture overview
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-bus driver
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-dprc driver
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-allocator
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-dpio driver
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-Ethernet
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-mac
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DPAA2 Overview
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--------------
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DPAA2 is a hardware architecture designed for high-speeed network
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packet processing. DPAA2 consists of sophisticated mechanisms for
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processing Ethernet packets, queue management, buffer management,
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autonomous L2 switching, virtual Ethernet bridging, and accelerator
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(e.g. crypto) sharing.
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A DPAA2 hardware component called the Management Complex (or MC) manages the
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DPAA2 hardware resources. The MC provides an object-based abstraction for
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software drivers to use the DPAA2 hardware.
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The MC uses DPAA2 hardware resources such as queues, buffer pools, and
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network ports to create functional objects/devices such as network
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interfaces, an L2 switch, or accelerator instances.
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The MC provides memory-mapped I/O command interfaces (MC portals)
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which DPAA2 software drivers use to operate on DPAA2 objects:
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+--------------------------------------+
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| OS |
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| DPAA2 drivers |
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| | |
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+-----------------------------|--------+
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| (create,discover,connect
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| config,use,destroy)
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DPAA2 |
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+------------------------| mc portal |-+
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| | |
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| +- - - - - - - - - - - - -V- - -+ |
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| | | |
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| | Management Complex (MC) | |
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| | | |
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| +- - - - - - - - - - - - - - - -+ |
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| |
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| Hardware Hardware |
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| Resources Objects |
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| --------- ------- |
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| -queues -DPRC |
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| -buffer pools -DPMCP |
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| -Eth MACs/ports -DPIO |
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| -network interface -DPNI |
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| profiles -DPMAC |
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| -queue portals -DPBP |
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| -MC portals ... |
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| ... |
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| |
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+--------------------------------------+
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The MC mediates operations such as create, discover,
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connect, configuration, and destroy. Fast-path operations
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on data, such as packet transmit/receive, are not mediated by
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the MC and are done directly using memory mapped regions in
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DPIO objects.
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Overview of DPAA2 Objects
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-------------------------
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The section provides a brief overview of some key objects
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in the DPAA2 hardware. A simple scenario is described illustrating
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the objects involved in creating a network interfaces.
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-DPRC (Datapath Resource Container)
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A DPRC is an container object that holds all the other
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types of DPAA2 objects. In the example diagram below there
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are 8 objects of 5 types (DPMCP, DPIO, DPBP, DPNI, and DPMAC)
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in the container.
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+---------------------------------------------------------+
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| DPRC |
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| |
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| +-------+ +-------+ +-------+ +-------+ +-------+ |
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| | DPMCP | | DPIO | | DPBP | | DPNI | | DPMAC | |
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| +-------+ +-------+ +-------+ +---+---+ +---+---+ |
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| | DPMCP | | DPIO | |
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| +-------+ +-------+ |
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| | DPMCP | |
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| +-------+ |
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| |
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+---------------------------------------------------------+
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From the point of view of an OS, a DPRC is bus-like. Like
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a plug-and-play bus, such as PCI, DPRC commands can be used to
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enumerate the contents of the DPRC, discover the hardware
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objects present (including mappable regions and interrupts).
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dprc.1 (bus)
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+--+--------+-------+-------+-------+
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| | | | |
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dpmcp.1 dpio.1 dpbp.1 dpni.1 dpmac.1
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dpmcp.2 dpio.2
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dpmcp.3
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Hardware objects can be created and destroyed dynamically, providing
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the ability to hot plug/unplug objects in and out of the DPRC.
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A DPRC has a mappable mmio region (an MC portal) that can be used
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to send MC commands. It has an interrupt for status events (like
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hotplug).
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All objects in a container share the same hardware "isolation context".
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This means that with respect to an IOMMU the isolation granularity
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is at the DPRC (container) level, not at the individual object
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level.
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DPRCs can be defined statically and populated with objects
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via a config file passed to the MC when firmware starts
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it. There is also a Linux user space tool called "restool"
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that can be used to create/destroy containers and objects
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dynamically.
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-DPAA2 Objects for an Ethernet Network Interface
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A typical Ethernet NIC is monolithic-- the NIC device contains TX/RX
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queuing mechanisms, configuration mechanisms, buffer management,
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physical ports, and interrupts. DPAA2 uses a more granular approach
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utilizing multiple hardware objects. Each object has specialized
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functions, and are used together by software to provide Ethernet network
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interface functionality. This approach provides efficient use of finite
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hardware resources, flexibility, and performance advantages.
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The diagram below shows the objects needed for a simple
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network interface configuration on a system with 2 CPUs.
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+---+---+ +---+---+
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CPU0 CPU1
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+---+---+ +---+---+
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| |
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+---+---+ +---+---+
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DPIO DPIO
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+---+---+ +---+---+
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\ /
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\ /
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\ /
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+---+---+
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DPNI --- DPBP,DPMCP
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+---+---+
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+---+---+
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DPMAC
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+---+---+
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port/PHY
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Below the objects are described. For each object a brief description
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is provided along with a summary of the kinds of operations the object
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supports and a summary of key resources of the object (mmio regions
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and irqs).
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-DPMAC (Datapath Ethernet MAC): represents an Ethernet MAC, a
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hardware device that connects to an Ethernet PHY and allows
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physical transmission and reception of Ethernet frames.
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-mmio regions: none
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-irqs: dpni link change
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-commands: set link up/down, link config, get stats,
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irq config, enable, reset
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-DPNI (Datapath Network Interface): contains TX/RX queues,
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network interface configuration, and rx buffer pool configuration
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mechanisms.
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-mmio regions: none
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-irqs: link state
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-commands: port config, offload config, queue config,
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parse/classify config, irq config, enable, reset
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-DPIO (Datapath I/O): provides interfaces to enqueue and dequeue
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packets and do hardware buffer pool management operations. For
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optimum performance there is typically DPIO per CPU. This allows
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each CPU to perform simultaneous enqueue/dequeue operations.
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-mmio regions: queue operations, buffer mgmt
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-irqs: data availability, congestion notification, buffer
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pool depletion
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-commands: irq config, enable, reset
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-DPBP (Datapath Buffer Pool): represents a hardware buffer
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pool.
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-mmio regions: none
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-irqs: none
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-commands: enable, reset
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-DPMCP (Datapath MC Portal): provides an MC command portal.
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Used by drivers to send commands to the MC to manage
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objects.
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-mmio regions: MC command portal
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-irqs: command completion
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-commands: irq config, enable, reset
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Object Connections
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------------------
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Some objects have explicit relationships that must
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be configured:
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-DPNI <--> DPMAC
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-DPNI <--> DPNI
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-DPNI <--> L2-switch-port
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A DPNI must be connected to something such as a DPMAC,
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another DPNI, or L2 switch port. The DPNI connection
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is made via a DPRC command.
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+-------+ +-------+
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| DPNI | | DPMAC |
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+---+---+ +---+---+
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| |
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+==========+
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-DPNI <--> DPBP
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A network interface requires a 'buffer pool' (DPBP
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object) which provides a list of pointers to memory
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where received Ethernet data is to be copied. The
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Ethernet driver configures the DPBPs associated with
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the network interface.
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Interrupts
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----------
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All interrupts generated by DPAA2 objects are message
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interrupts. At the hardware level message interrupts
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generated by devices will normally have 3 components--
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1) a non-spoofable 'device-id' expressed on the hardware
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bus, 2) an address, 3) a data value.
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In the case of DPAA2 devices/objects, all objects in the
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same container/DPRC share the same 'device-id'.
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For ARM-based SoC this is the same as the stream ID.
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DPAA2 Linux Driver Overview
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---------------------------
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This section provides an overview of the Linux kernel drivers for
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DPAA2-- 1) the bus driver and associated "DPAA2 infrastructure"
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drivers and 2) functional object drivers (such as Ethernet).
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As described previously, a DPRC is a container that holds the other
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types of DPAA2 objects. It is functionally similar to a plug-and-play
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bus controller.
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Each object in the DPRC is a Linux "device" and is bound to a driver.
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The diagram below shows the Linux drivers involved in a networking
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scenario and the objects bound to each driver. A brief description
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of each driver follows.
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+------------+
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| OS Network |
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| Stack |
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+------------+ +------------+
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| Allocator |. . . . . . . | Ethernet |
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|(dpmcp,dpbp)| | (dpni) |
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+-.----------+ +---+---+----+
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. . ^ |
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. . <data avail, | |<enqueue,
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. . tx confirm> | | dequeue>
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+-------------+ . | |
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| DPRC driver | . +---+---V----+ +---------+
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| (dprc) | . . . . . .| DPIO driver| | MAC |
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+----------+--+ | (dpio) | | (dpmac) |
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| +------+-----+ +-----+---+
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|<dev add/remove> | |
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+----+--------------+ | +--+---+
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| mc-bus driver | | | PHY |
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| | | |driver|
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| /fsl-mc@80c000000 | | +--+---+
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+-------------------+ | |
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================================ HARDWARE =========|=================|======
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DPIO |
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DPNI---DPBP |
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DPMAC |
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PHY ---------------+
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===================================================|========================
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A brief description of each driver is provided below.
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mc-bus driver
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-------------
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The mc-bus driver is a platform driver and is probed from an
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"/fsl-mc@xxxx" node in the device tree passed in by boot firmware.
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It is responsible for bootstrapping the DPAA2 kernel infrastructure.
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Key functions include:
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-registering a new bus type named "fsl-mc" with the kernel,
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and implementing bus call-backs (e.g. match/uevent/dev_groups)
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-implemeting APIs for DPAA2 driver registration and for device
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add/remove
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-creates an MSI irq domain
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-do a device add of the 'root' DPRC device, which is needed
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to bootstrap things
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DPRC driver
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-----------
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The dprc-driver is bound DPRC objects and does runtime management
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of a bus instance. It performs the initial bus scan of the DPRC
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and handles interrupts for container events such as hot plug.
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Allocator
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----------
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Certain objects such as DPMCP and DPBP are generic and fungible,
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and are intended to be used by other drivers. For example,
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the DPAA2 Ethernet driver needs:
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-DPMCPs to send MC commands, to configure network interfaces
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-DPBPs for network buffer pools
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The allocator driver registers for these allocatable object types
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and those objects are bound to the allocator when the bus is probed.
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The allocator maintains a pool of objects that are available for
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allocation by other DPAA2 drivers.
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DPIO driver
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-----------
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The DPIO driver is bound to DPIO objects and provides services that allow
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other drivers such as the Ethernet driver to receive and transmit data.
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Key services include:
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-data availability notifications
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-hardware queuing operations (enqueue and dequeue of data)
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-hardware buffer pool management
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There is typically one DPIO object per physical CPU for optimum
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performance, allowing each CPU to simultaneously enqueue
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and dequeue data.
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The DPIO driver operates on behalf of all DPAA2 drivers
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active in the kernel-- Ethernet, crypto, compression,
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etc.
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Ethernet
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--------
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The Ethernet driver is bound to a DPNI and implements the kernel
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interfaces needed to connect the DPAA2 network interface to
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the network stack.
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Each DPNI corresponds to a Linux network interface.
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MAC driver
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----------
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An Ethernet PHY is an off-chip, board specific component and is managed
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by the appropriate PHY driver via an mdio bus. The MAC driver
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plays a role of being a proxy between the PHY driver and the
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MC. It does this proxy via the MC commands to a DPMAC object.
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@ -1,7 +1,3 @@
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* Add README file (with ASCII art) describing relationships between
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DPAA2 objects and how combine them to make a NIC, an LS2 switch, etc.
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Also, define all acronyms used.
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* Decide if multiple root fsl-mc buses will be supported per Linux instance,
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and if so add support for this.
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