11. DPAA2 Poll Mode Driver

11.1.1. DPAA2 Overview

Reference: FSL MC BUS in Linux Kernel.

DPAA2 is a hardware architecture designed for high-speed 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.

11.1.2. 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. There is also a Linux user space tool called “restool” that can be used to create/destroy containers and objects dynamically.

11.1.3. 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

11.1.4. 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.

11.1.5. 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.

11.2.1. DPAA2 bus driver

The DPAA2 bus driver is a rte_bus driver which scans the fsl-mc bus. Key functions include:

• Reading the container and setting up vfio group
• Scanning and parsing the various MC objects and adding them to their respective device list.

Additionally, it also provides the object driver for generic MC objects.

11.2.2. 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 – Ethernet, crypto, compression, etc.

11.2.3. DPBP based Mempool driver

The DPBP driver is bound to a DPBP objects and provides sevices to create a hardware offloaded packet buffer mempool.

11.2.4. DPAA2 NIC 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 DPDK network interface.

11.5.1. Config File Options

The following options can be modified in the config file. Please note that enabling debugging options may affect system performance.

• CONFIG_RTE_LIBRTE_FSLMC_BUS (default n)

  By default it is enabled only for defconfig_arm64-dpaa2-* config. Toggle compilation of the librte_bus_fslmc driver.

• CONFIG_RTE_LIBRTE_DPAA2_PMD (default n)

  By default it is enabled only for defconfig_arm64-dpaa2-* config. Toggle compilation of the librte_pmd_dpaa2 driver.

• CONFIG_RTE_LIBRTE_DPAA2_DEBUG_DRIVER (default n)

  Toggle display of debugging messages/logic

• CONFIG_RTE_LIBRTE_DPAA2_USE_PHYS_IOVA (default y)

  Toggle to use physical address vs virtual address for hardware accelerators.

11.9.1. Platform Requirement

DPAA2 drivers for DPDK can only work on NXP SoCs as listed in the Supported DPAA2 SoCs.

11.9.2. Maximum packet length

The DPAA2 SoC family support a maximum of a 10240 jumbo frame. The value is fixed and cannot be changed. So, even when the rxmode.max_rx_pkt_len member of struct rte_eth_conf is set to a value lower than 10240, frames up to 10240 bytes can still reach the host interface.

11.9.3. Other Limitations

• RSS hash key cannot be modified.
• RSS RETA cannot be configured.
• Secondary process packet I/O is not supported.