..  SPDX-License-Identifier: BSD-3-Clause
    Copyright (c) 2015-2020 Amazon.com, Inc. or its affiliates.
    All rights reserved.

ENA Poll Mode Driver
====================

The ENA PMD is a DPDK poll-mode driver for the Amazon Elastic
Network Adapter (ENA) family.

Supported ENA adapters
----------------------

Current ENA PMD supports the following ENA adapters including:

* ``1d0f:ec20`` - ENA VF
* ``1d0f:ec21`` - ENA VF RSERV0

Supported features
------------------

* MTU configuration
* Jumbo frames up to 9K
* IPv4/TCP/UDP checksum offload
* TSO offload
* Multiple receive and transmit queues
* RSS hash
* RSS indirection table configuration
* Low Latency Queue for Tx
* Basic and extended statistics
* LSC event notification
* Watchdog (requires handling of timers in the application)
* Device reset upon failure
* Rx interrupts

Overview
--------

The ENA driver exposes a lightweight management interface with a
minimal set of memory mapped registers and an extendable command set
through an Admin Queue.

The driver supports a wide range of ENA adapters, is link-speed
independent (i.e., the same driver is used for 10GbE, 25GbE, 40GbE,
etc.), and it negotiates and supports an extendable feature set.

ENA adapters allow high speed and low overhead Ethernet traffic
processing by providing a dedicated Tx/Rx queue pair per CPU core.

The ENA driver supports industry standard TCP/IP offload features such
as checksum offload and TCP transmit segmentation offload (TSO).

Receive-side scaling (RSS) is supported for multi-core scaling.

Some of the ENA devices support a working mode called Low-latency
Queue (LLQ), which saves several more microseconds.

Management Interface
--------------------

ENA management interface is exposed by means of:

* Device Registers
* Admin Queue (AQ) and Admin Completion Queue (ACQ)

ENA device memory-mapped PCIe space for registers (MMIO registers)
are accessed only during driver initialization and are not involved
in further normal device operation.

AQ is used for submitting management commands, and the
results/responses are reported asynchronously through ACQ.

ENA introduces a very small set of management commands with room for
vendor-specific extensions. Most of the management operations are
framed in a generic Get/Set feature command.

The following admin queue commands are supported:

* Create I/O submission queue
* Create I/O completion queue
* Destroy I/O submission queue
* Destroy I/O completion queue
* Get feature
* Set feature
* Get statistics

Refer to ``ena_admin_defs.h`` for the list of supported Get/Set Feature
properties.

Data Path Interface
-------------------

I/O operations are based on Tx and Rx Submission Queues (Tx SQ and Rx
SQ correspondingly). Each SQ has a completion queue (CQ) associated
with it.

The SQs and CQs are implemented as descriptor rings in contiguous
physical memory.

Refer to ``ena_eth_io_defs.h`` for the detailed structure of the descriptor

The driver supports multi-queue for both Tx and Rx.

Configuration
-------------

Runtime Configuration
^^^^^^^^^^^^^^^^^^^^^

   * **llq_policy** (default 1)

     Controls whether use device recommended header policy or override it:

     0 - Disable LLQ (Use with extreme caution as it leads to a huge performance
     degradation on AWS instances built with Nitro v4 onwards).

     1 - Accept device recommended LLQ policy (Default).

     2 - Enforce normal LLQ policy.

     3 - Enforce large LLQ policy.

   * **miss_txc_to** (default 5)

     Number of seconds after which the Tx packet will be considered missing.
     If the missing packets number will exceed dynamically calculated threshold,
     the driver will trigger the device reset which should be handled by the
     application. Checking for missing Tx completions happens in the driver's
     timer service. Setting this parameter to 0 disables this feature. Maximum
     allowed value is 60 seconds.

   * **control_poll_interval** (default 0)

     Enable polling-based functionality of the admin queues,
     eliminating the need for interrupts in the control-path:

     0 - Disable (Admin queue will work in interrupt mode).

     [500..1000] - Time in milliseconds to wait between periodic checks of the admin queues.
     If a value outside this range is specified, the driver will automatically adjust it
     to fit within the valid range.

     **A non-zero value for this devarg is mandatory for control path functionality
     when binding ports to uio_pci_generic kernel module which lacks interrupt support.**


ENA Configuration Parameters
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

   * **Number of Queues**

     This is the requested number of queues upon initialization, however, the actual
     number of receive and transmit queues to be created will be the minimum between
     the maximal number supported by the device and number of queues requested.

   * **Size of Queues**

     This is the requested size of receive/transmit queues, while the actual size
     will be the minimum between the requested size and the maximal receive/transmit
     supported by the device.

Building DPDK
-------------

See the :ref:`DPDK Getting Started Guide for Linux <linux_gsg>` for
instructions on how to build DPDK.

By default the ENA PMD library will be built into the DPDK library.

For configuring and using UIO and VFIO frameworks, please also refer :ref:`the
documentation that comes with DPDK suite <linux_gsg>`.

Supported Operating Systems
---------------------------

Any Linux distribution fulfilling the conditions described in ``System Requirements``
section of :ref:`the DPDK documentation <linux_gsg>` or refer to *DPDK Release Notes*.

Prerequisites
-------------

#. Prepare the system as recommended by DPDK suite.  This includes environment
   variables, hugepages configuration, tool-chains and configuration.

#. ENA PMD can operate with ``vfio-pci`` (*), ``igb_uio``, or ``uio_pci_generic`` driver.

   (*) ENAv2 hardware supports Low Latency Queue v2 (LLQv2). This feature
   reduces the latency of the packets by pushing the header directly through
   the PCI to the device, before the DMA is even triggered. For proper work
   kernel PCI driver must support write-combining (WC).
   In DPDK ``igb_uio`` it must be enabled by loading module with
   ``wc_activate=1`` flag (example below). However, mainline's vfio-pci
   driver in kernel doesn't have WC support yet (planned to be added).
   If vfio-pci is used user should follow `AWS ENA PMD documentation
   <https://github.com/amzn/amzn-drivers/tree/master/userspace/dpdk/README.md>`_.

#. For ``igb_uio``:
   Insert ``igb_uio`` kernel module using the command ``modprobe uio; insmod igb_uio.ko wc_activate=1``

#. For ``vfio-pci``:
   Insert ``vfio-pci`` kernel module using the command ``modprobe vfio-pci``
   Please make sure that ``IOMMU`` is enabled in your system,
   or use ``vfio`` driver in ``noiommu`` mode::

     echo 1 > /sys/module/vfio/parameters/enable_unsafe_noiommu_mode

   To use ``noiommu`` mode, the ``vfio-pci`` must be built with flag
   ``CONFIG_VFIO_NOIOMMU``.

#. For ``uio_pci_generic``:
   Insert ``uio_pci_generic`` kernel module using the command ``modprobe uio_pci_generic``.
   Make sure that the IOMMU is disabled or is in passthrough mode.
   For example: ``modprobe uio_pci_generic intel_iommu=off``.

   Note that when launching the application,
   the ``control_poll_interval`` devarg must be used with a non-zero value (1000 is recommended)
   as ``uio_pci_generic`` lacks interrupt support.
   The control-path (admin queues) of the ENA requires poll-mode
   to process command completion and asynchronous notification from the device.
   For example: ``dpdk-app -a "00:06.0,control_path_poll_interval=1000"``.

#. Bind the intended ENA device to ``vfio-pci``, ``igb_uio``, or ``uio_pci_generic`` module.

At this point the system should be ready to run DPDK applications. Once the
application runs to completion, the ENA can be detached from attached module if
necessary.

**Rx interrupts support**

ENA PMD supports Rx interrupts, which can be used to wake up lcores waiting for input.
Please note that it won't work with ``igb_uio`` and ``uio_pci_generic``
so to use this feature, the ``vfio-pci`` should be used.

ENA handles admin interrupts and AENQ notifications on separate interrupt.
There is possibility that there won't be enough event file descriptors to
handle both admin and Rx interrupts. In that situation the Rx interrupt request
will fail.

**Note about usage on \*.metal instances**

On AWS, the metal instances are supporting IOMMU for both arm64 and x86_64 hosts.
Note that ``uio_pci_generic`` lacks IOMMU support and cannot be used for metal instances.

* x86_64 (e.g. c5.metal, i3.metal):
   IOMMU should be disabled by default. In that situation, the ``igb_uio`` can
   be used as it is but ``vfio-pci`` should be working in no-IOMMU mode (please
   see above).

   When IOMMU is enabled, ``igb_uio`` cannot be used as it's not supporting this
   feature, while ``vfio-pci`` should work without any changes.
   To enable IOMMU on those hosts, please update ``GRUB_CMDLINE_LINUX`` in file
   ``/etc/default/grub`` with the below extra boot arguments::

    iommu=1 intel_iommu=on

   Then, make the changes live by executing as a root::

    # grub2-mkconfig > /boot/grub2/grub.cfg

   Finally, reboot should result in IOMMU being enabled.

* arm64 (a1.metal):
   IOMMU should be enabled by default. Unfortunately, ``vfio-pci`` isn't
   supporting SMMU, which is implementation of IOMMU for arm64 architecture and
   ``igb_uio`` isn't supporting IOMMU at all, so to use DPDK with ENA on those
   hosts, one must disable IOMMU. This can be done by updating
   ``GRUB_CMDLINE_LINUX`` in file ``/etc/default/grub`` with the extra boot
   argument::

    iommu.passthrough=1

   Then, make the changes live by executing as a root::

    # grub2-mkconfig > /boot/grub2/grub.cfg

   Finally, reboot should result in IOMMU being disabled.
   Without IOMMU, ``igb_uio`` can be used as it is but ``vfio-pci`` should be
   working in no-IOMMU mode (please see above).

Usage example
-------------

Follow instructions available in the document
:ref:`compiling and testing a PMD for a NIC <pmd_build_and_test>` to launch
**testpmd** with Amazon ENA devices managed by librte_net_ena.

Example output:

.. code-block:: console

   [...]
   EAL: PCI device 0000:00:06.0 on NUMA socket -1
   EAL: Device 0000:00:06.0 is not NUMA-aware, defaulting socket to 0
   EAL:   probe driver: 1d0f:ec20 net_ena

   Interactive-mode selected
   testpmd: create a new mbuf pool <mbuf_pool_socket_0>: n=171456, size=2176, socket=0
   testpmd: preferred mempool ops selected: ring_mp_mc
   Warning! port-topology=paired and odd forward ports number, the last port will pair with itself.
   Configuring Port 0 (socket 0)
   Port 0: 00:00:00:11:00:01
   Checking link statuses...

   Done
   testpmd>