kernel – Bootlin

Congatec Board Controller support into the upstream Linux Kernel

Introduction

Congatec’s x86 System-on-Modules (SoM) include a Board Controller component connected to the processor via an eSPI bus, and providing various features such as I²C buses, GPIOs, a watchdog timer, and various sensors for monitoring voltage, fan speed, and more.

For their x86 System-on-Modules (SoMs), Congatec provides a Yocto meta-layer: meta-congatec-x86. This meta-layer includes, among other components, a driver, a library, and tools for interfacing with the Board Controller.

The primary issue with the provided driver is its deviation from standard Linux APIs. It exposes a custom character device and relies on custom ioctl() for communication with userspace. This non-standard approach leads to compatibility and portability challenges. For example, an application using the standard Linux GPIO API would need to be adapted to access the GPIOs from Congatec’s Board Controller. Similarly, software designed specifically for the Board Controller’s GPIOs would require changes to work with GPIOs on other platforms.

Additionally, because the driver is out-of-tree, it raises concerns about long-term support and maintainability. Questions naturally arise—will the driver be regularly updated to remain compatible with future Linux kernel versions, given the instability of internal APIs? Will bugs and security vulnerabilities be addressed in a timely manner?

One of our customers, planning to use the Conga-SA7 board in a commercial product, recognized these challenges early on. As a result, they asked us to integrate support for the Congatec Board Controller directly into the mainline Linux kernel. Upstreaming the driver into the kernel would eliminate these issues by ensuring better portability, long-term maintenance, and community support.

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Bouncing on trampolines to run eBPF programs

This blog post is the second installment in our eBPF blog post series, following our blog post about eBPF selftests.

As eBPF is more and more used in the industry, eBPF kernel developers give considerable attention to eBPF performance: some standard use cases like system monitoring involve hundreds of eBPF programs attached to events triggered at high frequencies. It is then paramount to keep eBPF programs execution overhead as low as possible. This blog post aims to shed some light on an internal eBPF mechanism perfectly showcasing those efforts: the eBPF trampoline.

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Linux 6.16 released, Bootlin contributions

Penguin coding, AI generated Linux 6.16 was released last Sunday, and as usual LWN provides the best coverage of what’s new: part 1 and part 2, as well as the KernelNewbies.org page for this release.

This time around, the engineers at Bootlin contributed 89 patches to the 6.16 release, but also as maintainers, they reviewed/merged 117 patches from other contributors!

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Linux 6.15 released, Bootlin contributions inside

Penguin coding, AI generated Linux 6.15 has been released last Sunday, and we as usual encourage our readers to look at the LWN summaries of the merge window (part 1, part 2) for a good summary. CNX-Software also has a summary more oriented towards hardware support for ARM and RISC-V platforms.

On our side, we have been quite active in this release cycle, with no less than 145 commits from Bootlin engineers merged. Also, our engineers who maintain various subsystems in the Linux kernel reviewed and merged a total of 104 patches from other contributors.

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Announcing our new Embedded Linux Networking training course

We are proud to announce the launch of a brand new addition to our lineup of training courses: Embedded Linux Networking!

This training course is designed to provide embedded Linux engineers with a deep and practical understanding of networking concepts and their implementation in both the Linux kernel and user-space — with a strong focus on real-world embedded applications.
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Demystifying the Kernel Boot Sequence: From ‘Starting Kernel…’ to Userspace”

Board booting

As kernel developers, we often find ourselves writing device drivers—pieces of code that are typically registered using module_init() in the Linux kernel. But have you ever paused to wonder: just how late in the boot process does this happen? What exactly takes place between the moment we see the famous "Starting kernel..." message and the point where drivers are finally registered and devices probed?

If you’re curious about the intricate steps that occur before the system even reaches a working init process, you’re in the right place. Join us as we explore the fascinating journey of the Linux kernel boot sequence—step by step.

Throughout this article, you’ll find clickable links to our Elixir source code browser. We encourage you to dive in and follow along!

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Back from Netdev 0x19

Around mid-March, Bootlin engineers Köry Maincent and Romain Gantois had the chance to attend edition 0x19 of the Netdev conference, where developers from the Linux kernel networking community assemble for four days of technical presentations and discussions.

They were generally very much impressed by the quality and detail of the talks given during this conference, and they have selected two of the talks that they found the most interesting, which they summarized below. We expect the slides and videos to be published at some point in the future, but they don’t seem to be available at the moment.

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Linux 6.14 released, Bootlin contributions inside

Penguin coding, AI generated Linux 6.14 was released last week, and as usual, we recommend checking out the LWN articles covering the 6.14 merge window (part 1, part 2) to get a good sense of the main new features and updates in this release.

Bootlin engineers have once again been busy contributing to this kernel release, with 125 commits authored by Bootlin engineers, and 60 patches reviewed and merged by Bootlin engineers who are maintainers of specific parts of the Linux kernel.

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Bootlin at Netdev 0x19, THE Technical Conference on Linux Networking

The Netdev conference is THE annual event dedicated to Linux networking, featuring numerous talks, presentations, and discussions on all aspects of network support in the Linux kernel and ecosystem. It takes place this year on March 10-13 in Zagreb, Croatia.

Given the importance of these topics to Bootlin, our engineers Köry Maincent and Romain Gantois are attending in person. Köry has contributed to Linux’s new Power over Ethernet support and improvements in PTP timestamping flexibility, while Romain is actively working on SFP support. Additionally, Bootlin networking expert Maxime Chevallier will be following the conference remotely.

Attending Netdev is essential for Bootlin, enabling our engineers to stay at the forefront of Linux networking advancements, collaborate with key contributors, and take part in discussions shaping the future of networking in the Linux kernel. By actively participating, we ensure that Bootlin continues to make meaningful contributions to the ecosystem while strengthening our expertise to better support our customers and open-source initiatives.

Bootlin Training: In-person public sessions are back!

Icon from www.flaticon.com Bootlin training courses have long been recognized for their quality and effectiveness. Before the COVID era, we offered in-person sessions either on-site at customer locations for larger groups or as public sessions at our facilities, bringing together engineers from multiple companies. However, with the onset of the pandemic, we transitioned exclusively to online training. Since then, we have resumed in-person sessions at customer locations, but public sessions have yet to make a comeback—until now.

We’re excited to announce the return of our in-person public training sessions! The first session will focus on Linux kernel driver development and is scheduled for June 16-20, 2025, in Lyon, France. This course will be conducted by none other than Bootlin engineer and Linux kernel maintainer Grégory Clement.

For participants who prefer an in-person learning experience, this session provides a valuable opportunity for direct interaction with our trainer and fellow attendees. It’s an excellent alternative to online sessions, fostering deeper engagement and collaboration.

Seats are available at the standard rate of 2100 EUR per participant, with a discounted rate of 2000 EUR per participant under certain conditions.

Beyond this Linux kernel driver development in-person public session, we have plans to also open in-person public sessions for our Embedded Linux system development, Yocto Project/OpenEmbedded system development and Debugging, tracing, profiling and performance analysis with Linux training courses. Do not hesitate to contact us if you’re interested. Your feedback will help us gauge interest and schedule these sessions accordingly.