Bootlin – Embedded Linux and kernel engineering

Device tree addons: describing non-discoverable addon boards and connectors

Lots of embedded devices exist that have a connector for addon boards: BeagleBone Black Capes and Raspberry Pi Hats are just some common de facto standards, each with a whole ecosystem of base boards and addon boards that can be mixed and matched in countless ways. Most of them are based on embedded System-on-Chips, and thus use device tree to describe their hardware. Yet there is no good way to describe the connectors and addons in an efficient, modular and effective way.

At Bootlin we have been working for a few years to implement a proper way of describing such addon boards and their connectors using device tree. We have found a huge interest in the embedded systems community, but the road to get there is steep.

Our initial effort based on device tree overlays was rejected due to fundamental shortcomings in the device tree overlay design at its root. After discussing with the community we are now proposing a totally new concept: device tree addons. It’s a huge work, a lot has been done but there is still a lot to be done.

This post introduces the rationale and use cases, shows a practical example, describes how to test our current proposal and, last but not least, suggests how to contribute to the mailing list discussion to help this work land upstream for everyone’s benefit.

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Welcome to Thomas Païta and Paul Cercueil

We recently welcomed two engineers to our team: Thomas Païta, based at our Lyon office, and Paul Cercueil, working from Madrid, Spain.

Thomas Païta

Thomas Païta Thomas joined Bootlin at the end of June 2026. After graduating from the Université de Technologie de Compiègne, he worked on embedded Linux and FreeRTOS at Sagemcom, followed by Rust and C++ development in the space industry. At Bootlin, his work will focus not only on Embedded Linux, but also on Zephyr.

Thomas is currently the 5th Thomas at Bootlin, joining Thomas Petazzoni, Thomas Perrot, Thomas Richard, and Thomas Bonnefille.

See his profile page for more details.

Paul Cercueil

Paul Cercueil Paul joined Bootlin in September 2026. After graduating in 2014 from the Université de Technologie de Belfort-Montbéliard, Paul worked at Analog Devices, where he designed and developed the ecosystem around Linux’ IIO subsystem and authored the companion libiio project. In addition to his work on IIO, Paul has extensive Linux kernel experience, with over 750 patches, mainly focused on supporting MIPS-based Ingenic SoCs, for which he is the platform maintainer. Paul also has a solid background in Buildroot, having been the main developer and maintainer of the Buildroot-based OpenDingux distribution, as well as contributing more than 60 patches to upstream Buildroot. Paul also enjoys tinkering with other retro-gaming console projects, including the KallistiOS project, an operating system for the SEGA Dreamcast, and a MIPS-to-everything JIT compiler for the PlayStation 1.

Paul is French and also speaks English and Spanish fluently. See his profile page for more details.

audio-iio-aux: when IIO meets audio

Some time ago, one of our customers came to us with a hardware design featuring the Renesas X9250 digital potentiometer in an audio path, as shown in the following diagram. Naturally, our goal was to find the proper way to support this hardware design in the upstream Linux kernel.

Audio path with potentiometer

Since the X9250 is part of an audio path, the first thing that came to mind was the ALSA subsystem of the Linux kernel. However, the Renesas X9250 is a generic digital potentiometer, and audio is only one of its many possible use cases.

The Linux kernel also has a separate subsystem called IIO (Industrial I/O), which provides support for a wide range of devices, including accelerometers, various types of sensors, ADCs, DACs, and potentiometers. Potentiometers are already supported by IIO, as can be seen in the drivers/iio/potentiometer directory.

IIO is not specific to audio, so implementing the Renesas X9250 driver as an IIO driver made more sense than implementing an ALSA-specific driver. This way, the same driver can be reused for non-audio use cases as well.

However, we still needed a way for the potentiometer to be handled as a regular component of an audio path through the ALSA subsystem.

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Bootlin toolchains 2026.08 released

We are happy to announce the release of a new version of our freely available, pre-compiled cross-compilation toolchains, hosted at toolchains.bootlin.com.

This update covers a range of 43 CPU architecture variants, including: aarch64, aarch64be, arcle-750d, arcle-hs38, armv5-eabi, armv6-eabihf, armv7-eabihf, armebv7-eabihf, armv7m, m68k-68xxx, m68k-coldfire, microblazebe, microblazeel, mips32, mips32el, mips32r5el, mips32r6el, mips64-n32, mips64el-n32, mips64r6el-n32, openrisc, powerpc-440fp, powerpc-e300c3, powerpc-e500mc, powerpc64-e5500, powerpc64-e6500, powerpc64-power8, powerpc64le-power8, riscv32-ilp32d, riscv64-lp64d, s390x-z13, sh-sh4, sh-sh4aeb, sparc64, sparcv8, x86-64, x86-64-v2, x86-64-v3, x86-64-v4, x86-64-core-i7, x86-core2, x86-i686, xtensa-lx60.

As with previous releases, we provide two editions of each toolchain: a stable version based on the N-1 releases of GCC, binutils, GDB, and slightly older kernel headers, and a bleeding edge version featuring the latest available components. For the 2026.08 release, the versions are:

The bleeding-edge toolchains are based on gcc 16.2, binutils 2.46.1, gdb 17.1, kernel headers 6.12, glibc 2.44, musl 1.2.6 or uclibc-ng 1.0.59.
The stable toolchains are based on gcc 15.3, binutils 2.45.1, gdb 16.3, kernel headers 5.10, glibc 2.44, musl 1.2.6 or uclibc-ng 1.0.59.

All toolchains are built for x86-64 Linux hosts and are compatible even with relatively old Linux distributions. We welcome bug reports and feedback through our project issue tracker.

Bootlin’s Yocto training course updated to Wrynose

The latest Long Term Support release of the Yocto Project, Yocto Project 6.0 (Wrynose), was released a few months ago, so it was time to update our Yocto Project training materials. This update is now complete.

As with every new Yocto Project release, Wrynose brings a number of changes and new features. Some of them affect the way developers work with Yocto, so we have updated our slides and labs accordingly. In particular:

The bitbake-setup tool was introduced as the Yocto Project-supported way to fetch layers and set up a build configuration. This has been a long-requested feature, and it is now covered in our training.
As part of this change, the Poky Git repository has been deprecated and is no longer maintained. Users now fetch the base components through a bitbake-setup configuration file or by using an external tool.
Support for configuration fragments was added, making it possible to group related and consistent configuration settings together. This is intended to simplify configuration management, whether or not bitbake-setup is being used. The new bitbake-config-build command can be used to enable these fragments from the command line.
There are also internal changes that affect how recipes should be written. These changes are reflected in our training materials. For example, the introduction of UNPACKDIR changes how the S and WORKDIR variables can be used.

Updated labs

We continue to support four different boards in our practical labs:

STM32MP157A-DK1
i.MX93 FRDM
BeaglePlay
BeagleBone Black

For each of these platforms, we use either vendor-provided or community-supported layers, each approach has its own advantages and limitations.

The labs have therefore been updated alongside the training slides to ensure that they remain aligned with the latest Yocto Project release.

Join our Yocto Project training

As with all Bootlin training courses, the Yocto Project training materials are freely available on our website.

If you would like to attend the training with an instructor, we offer public online sessions scheduled by Bootlin. We can also organize private online or private on-site sessions on demand.

Our next public sessions with available seats are:

Whether you are new to the Yocto Project or want to update your existing knowledge, our training provides both the concepts and hands-on experience needed to build and maintain embedded Linux systems with Yocto.

sbom-cve-check 1.3.2 and 1.3.3: improved SBOM handling and more robust CVE analysis

Since our previous update on sbom-cve-check, the project has continued to evolve with two new releases: version 1.3.2, released in June, and version 1.3.3, released in August.

These releases bring a number of improvements to the handling of SBOM data, CVE version ranges and vulnerability assessments, as well as fixes for some corner cases encountered when analyzing real-world software projects.

For those discovering the project, sbom-cve-check is a lightweight open-source tool developed by Bootlin for performing vulnerability analysis on Software Bill of Materials (SBOMs). It is based on SPDX SBOMs and can be used both as a standalone tool and through its integration in the Yocto Project. Since the Yocto Project’s Wrynose release, sbom-cve-check has been used as the Yocto Project’s official tool for CVE monitoring.

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yocto-kiss: updated to the Wrynose Yocto LTS release

We are pleased to announce that yocto-kiss, our minimal but realistic Yocto/OpenEmbedded reference setup, has been updated to the latest Wrynose Yocto LTS release (version 6.0). Following the addition of ZynqMP support and the move to a cleaner multi-layer architecture earlier this year, this update keeps the project aligned with the current Yocto LTS and brings several improvements we’d like to highlight.

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Snagboot v3.0 is released!

Snagboot has just received its second major version number increase since its initial release in 2023! The jump to 2.0 had been made to mark the introduction of Snagfactory, back in 2024. Almost two years have passed since then, and contributions to the project have been going strong! The milestone which underlies our decision to jump to 3.0 is a major overhaul of Snagfactory, turning it into a QT6-based app.

Let’s look back at some notable changes since the last release.

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Linux 7.2 released, Bootlin contributions inside

Tux Linux 7.2 has been released last Sunday afternoon. You can take a look at the whole content of this new version thanks to LWN merge window posts (see part 1 and part 2). As stated by Linus Torvalds himself, the final week of this release has not been a peaceful endeavour (with some late reverts being needed), but this phenomenon seems to be slowly becoming “the new normal thing”. You can find more details and facts about this release in the 7.2 coverage from LWN.

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Understanding the Linux Graphics Stack is now available as a self-paced video course

Bootlin’s Understanding the Linux Graphics Stack training course is now available as a self-paced, pre-recorded video course on Udemy.

This course has previously been offered as an instructor-led training course. We are now changing its format: it is no longer available as an instructor-led course and is instead offered as a pre-recorded course that you can follow at your own pace.

For now, Understanding the Linux Graphics Stack is the only Bootlin training course available in a self-paced format. All of our other training courses continue to be offered as instructor-led training sessions.

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