.. SPDX-License-Identifier: BSD-3-Clause
   Copyright 2024 The DPDK contributors


Adding a New Driver
===================

The DPDK project continuously grows its ecosystem by adding support for new devices.
This document assists contributors in creating DPDK drivers,
also known as Poll Mode Drivers (PMD).

By having public support for a device, we ensure accessibility across various
operating systems and guarantee community maintenance in future releases.
If a new device is similar to a device already supported by an existing driver,
it is more efficient to update the existing driver.

Here are our best practice recommendations for creating a new driver.


Early Engagement with the Community
-----------------------------------

When creating a new driver, engage with the DPDK community early
rather than waiting for the work to mature.

These public discussions help align development of your driver with DPDK expectations.
You may submit a roadmap before the release to inform the community of your plans.
Additionally, sending a Request For Comments (RFC) early in the release cycle,
or even during the prior release, is advisable.

DPDK is mainly consumed via Long Term Support (LTS) releases.
It is common to target a new PMD to an LTS release.
For this, start upstreaming at least one release before an LTS release.


Progressive Work
----------------

To continually progress your work, plan
for incremental upstreaming across multiple patch series or releases.

Prioritize quality of the driver over upstreaming
in a single release or single patch series.


Finalizing
----------

Once the driver is upstreamed,
the author is responsible for maintaining it.

This includes the public test report.
Authors must send a public test report after the first upstreaming of the PMD.
The same public test procedure may be reproduced regularly per release.

After the PMD is upstreamed, send a patch to update
`the website <https://core.dpdk.org/supported/>`_
with the name of the new PMD and supported devices via the
`DPDK web mailing list <https://mails.dpdk.org/listinfo/web>`_.

For more information about the role of maintainers, see :doc:`patches`.


Splitting into Patches
----------------------

Split drivers into patches
so that each patch represents a single feature.
If the driver code is already developed, it may be challenging to split.
However, there are many benefits to doing so.

Splitting patches makes it easier to understand a feature
and clarifies the list of components/files that compose that specific feature.

It also enables the ability to track
from the source code to the feature it enables,
and helps users understand the reasoning and intention of implementation.
This kind of tracing is regularly required for defect resolution and refactoring.

Another benefit of splitting the codebase per feature is that
it highlights unnecessary or irrelevant code,
as any code not belonging to any specific feature becomes obvious.

Git bisect is also more useful if patches are split per feature.

Focus the split on logical features rather than file-based divisions.

Each patch in the series must compile without errors
and should maintain functionality.

Enable the build as early as possible within the series
to facilitate continuous integration and testing.
This approach ensures a clear and manageable development process.

Split patches following this approach:

* Organize each patch logically as a new feature.
* Run test tools per patch (See :ref:`contrib_tool_list`).
* Update relevant documentation and `<driver>.ini` file with each patch.

The following order in the patch series is as suggested below.

The first patch should have the driver's skeleton which should include:

* Maintainers file update
* Driver documentation
* Document must have links to official product documentation web page
* Add the new document to the index (`index.rst`)
* Initial `<driver>.ini` file
* Release notes announcement for the new driver

The next patches should include basic device features.
The following is a suggested sample list of such patches:

================================  ================================
Net                               Crypto
================================  ================================
Initialization                    Initialization
Configure queues                  Configure queues
Start queues                      Configure sessions
Simple Rx / Tx                    Add capabilities
Statistics                        Statistics and device info
Device info                       Simple data processing
Link interrupt
Burst mode info
Promisc all-multicast
RSS
================================  ================================

Advanced features should be in the next group of patches.
The suggestions for these, listed below, are in no specific order:

================================  ================================
Net                               Crypto
================================  ================================
Advanced Rx / Tx                  Chained operations
Vector Rx / Tx                    Scatter Gather
Scatter support                   Security protocols (IPsec, etc.)
TSO / LRO                         Asymmetric crypto
Rx / Tx descriptor status
Rx / Tx queue info
Flow offload
Traffic management / metering
Extended statistics
Secondary process support
FreeBSD / Windows support
Flow control
FEC
EEPROM access
Register dump
Time synchronization, PTP
Performance documentation
================================  ================================

After enabling all features,
if there is remaining base code that is not upstreamed,
upstream it at the end of the patch series.
However, still split these patches into logical groups.


Additional Suggestions
----------------------

Avoid doing the following:

* Using PMD specific macros when DPDK macros exist
* Including unused headers (see `process-iwyu.py`)
* Disabling compiler warnings for a driver
* #ifdef with driver-defined macros
* DPDK version checks (via ``RTE_VERSION_NUM``) in the upstream code
* Introducing public API directly from the driver

Remember to do the following:

* Runtime configuration when applicable
* Document device parameters in the driver guide
* Make device operations struct 'const'
* Dynamic logging
* SPDX license tags and copyright notice on each file
* Run the Coccinelle scripts `devtools/cocci.sh`
  which check for common cleanups
  such as useless null checks before calling free routines


Dependencies
------------

At times, drivers may have dependencies on external software.
For driver dependencies, the same DPDK rules for dependencies apply.
Dependencies should be publicly and freely available;
drivers that depend on unavailable components will not be accepted.
If the required dependency is not yet publicly available,
wait to submit the driver until the dependent library is available.


.. _contrib_tool_list:

Test Tools
----------

Build and check the driver's documentation.
Ensure there are no warnings
and the driver shows up in the relevant index page.

Run the following test tools per patch in a patch series:

* `checkpatches.sh`
* `check-git-log.sh`
* `check-meson.py`
* `check-doc-vs-code.sh`
* `check-spdx-tag.sh`
* Build documentation and validate how output looks
* Optionally run ``review-patch.py`` for AI-assisted review
  (see :ref:`contrib_ai_assisted_review` in the Contributing Guide)
