2018 at Bootlin, a year in review

First of all, the entire team at Bootlin wishes you a Happy New Year, and best wishes for 2019 in your personal and professional life. The beginning of the new year is a good time to look back and see the achievements of the past year, which is why we review the 2018 year in terms of Bootlin news and activity:

We’re now called Bootlin

Due to a legal battle related to trademarks, we decided to change our name to Bootlin at the beginning of 2018. The company was not sold or purchased, it is still owned by the same people, and driven by the same team of engineers. This change of name obviously took a lot of time, which could have been used for other more productive contribution activities, but it’s finally done, and in 2019 we can move on and leave this legal battle behind us. See our blog post for more details.

Kernel contributions

In 2018, we contributed to the 4.15, 4.16, 4.17, 4.18, 4.19 and 4.20 kernel releases a total of 1365 commits, putting Bootlin regularly in the top 20 companies contributing to the Linux kernel.

Our most significant contributions have been:

  • Thanks to a successful crowdfunding campaign launched in February, we have been able to dedicate enough time to develop and upstream a Linux kernel driver and associated user-space library to support hardware-accelerated video decoding on Allwinner processors. This was a massive effort as it required discussing with the Linux kernel community a new set of userspace interfaces to support stateless video decoders. The base of our driver was merged in Linux 4.20 and supports only MPEG2 decoding. Support for H264 and H265 decoding is ready and has been posted several times, but discussions on the userspace interface are still on-going. See our numerous blog posts and especially the end of year status.
  • We have developed and contributed a brand new Linux kernel subsystem to support the MIPI I3C bus, a modern bus offering an alternative to SPI or I2C. Being vastly different from I2C, it required a completely separate subsystem located in drivers/i3c/. Along with the core subsystem itself, we developed a driver for the Cadence I3C master, and a driver for a Cadence I3C GPIO expander. See our blog posts on I3C for more details.
  • We contributed a new interface called exec_op for NAND flash controller drivers, which allows the MTD subsystem to more easily support optimized NAND flash controllers and vendor-specific NAND commands. This new interface was originally developed for the Marvell NAND controller driver, but a number of other drivers have been converted since then, and all new drivers make use of his interface. See our blog post for more details.
  • We contributed support for the Microsemi VSC7513 and VSC7514 MIPS processors, with the base support (irqchip, pinctrl, gpio, reset, DT) but more importantly a massive switchdev driver to support the major feature of these processors: a built-in gigabit Ethernet switch. Our switchdev driver supports bridging, STP, IGMP snooping, VLAN filtering and link aggregation. See our blog posts about platform support and switchdev support.
  • We contributed a new subsystem called spi-mem, which allows to support SPI flash memories in a generic way, re-using SPI controller drivers for regular SPI devices, SPI NOR flashes and SPI NAND flashes, instead of having separate controller drivers as was done until now for SPI NOR support. On top of spi-mem, we added support for SPI NAND flash memories to Linux. See our blog post on spi-mem: bringing some consistency to the SPI memory ecosystem.
  • We contributed a number of drivers for Cadence hardware IPs: Cadence MIPI CSI receiver, Cadence MIPI CSI transceiver, Cadence DSI encoder, Cadence PCIe host controller, Cadence PCIe endpoint controller and as detailed above Cadence I3C master controller.
  • We continued to work on improving the support for Marvell ARM processors
    • Improvements in the inside-secure crypto accelerator driver: support for new crypto algorithms, support for the EIP97 variant which enabled using the driver on Armada 37xx in addition to the already support EIP197 variant used on Armada 7K/8K, numerous fixes and performance improvements
    • Improvements in the mvpp2 network controller driver, used on Armada 7K/8K: RSS support, support for SFP ports, HW offloading for VLAN filtering, 1000baseX and 2500baseX support
    • On Armada 7K/8K, we added support for the NAND controller and the thermal sensors.
    • On Armada 37xx, we added cpufreq support and the first pieces of suspend/resume support.
  • Allwinner platform support improvements: of course the Allwinner VPU driver detailed above, but also general improvements to the Allwinner A83 support (for which we delivered a complete BSP for a customer), improvements to the sun4i display driver (especially support for YUV planes, and MIPI DSI support on Allwinner A33), improvements to the sun8i-codec audio driver, and improvements to the AXP209 and AXP813 PMIC drivers.
  • For Microchip/Atmel platforms, we continued our maintenance work, with a focus this year on reworking the representation of the platform clocks in the Device Tree.

U-Boot contributions

Even if Bootlin is mainly active as a Linux kernel contributor, we also contribute to U-Boot, and we have been more active in 2018 than we were in the past. In a recent blog post, we summarized our most significant contributions:

  • Support for SPI NAND memories, as well as a significant sync of the MTD stack in U-Boot with the one from Linux, and the introduction of a generic mtd U-Boot command to manipulate all types of flash memories
  • Generic support for TPMv2 and for TPMv2 chips connected over SPI
  • Brand new subsystem to support 1-wire controllers and devices
  • Support for the Microsemi Ocelot and Luton MIPS processors. We also contributed support for Microsemi Ocelot to Linux, as discussed above
  • Support for the ARM PL022 SPI controller
  • Support for multiple U-Boot environment backends
  • Support for Microsemi VSC8574 and VSC8584 Ethernet PHYs

In total, we contributed 172 commits to U-Boot in 2018.

Other contributions

Beyond Linux and U-Boot, we also contributed to a few other open-source projects:

Other engineering projects

While many of our engineering projects are directly related to upstream contributions, which have been described above, some are not always leading to direct contributions. Here is a small selection of other interesting projects we worked on in 2018:

  • For a German customer in the healthcare industry, wrote a complete U-Boot, Linux and Buildroot BSP for a custom NXP i.MX6 platform.
  • For an international company in the TV/set-top box industry, worked on adding support for top-level parallel build to Buildroot.
  • For a Netherlands based customer in the gaming industry, wrote a complete U-Boot, Linux and Buildrot BSP for a custom Allwinner A33 platform, with significant boot time optimization to quickly boot up to a Qt5 OpenGL application.
  • For a Spanish customer, brought up a PCM1789 audio codec connected to a NXP i.MX6 processor, and for an Italian customer, brought up a CS4272 audio codec connected to an Allwinner A20 processor. Under Linux, of course!
  • We continued working for a major US customer, delivering an i.MX6 and SPEAr600 Linux BSP based on Yocto. Our work in 2018 was mainly focused on supporting secure boot on i.MX6 (see our talk at ELC on this topic) and porting a modern version of U-Boot on the SPEAr600 platform.
  • For a customer in Chile, we worked on supporting a OV5640 camera sensor connected over CSI to an Allwinner H3 platform. Thanks to this, we made a significant number of improvements to the OV5640 driver.
  • We have continued to maintain toolchains.bootlin.com, by keeping the toolchains reguarly updated, and adding support for the RISC-V 64 bit architecture. See our blog posts.


In 2018, Bootlin was at a large number of conferences and events:


In 2018, we gave our Embedded Linux, Linux kernel, Yocto Project and Buildroot training courses on-site in the United States, Portugal, Belgium, Germany, France, Spain, Serbia, Greece, Bosnia, Finland and Switzerland. As you can see, we travel all around the world to teach our training courses.

Of course, we continued our public training sessions organized in Avignon (France), given in English by Bootlin founder and CEO Michael Opdenacker.

In 2018, we made 217 commits to our training materials Git repository, showing our continuous work to keep them updated. Our training materials remain all freely available under a Creative Commons CC-BY-SA license, as they have been since Bootlin creation fifteen years ago.

Office expansion

In 2018, we expanded both our Toulouse and Lyon offices:

  • We moved our office in Toulouse mid-2018 from a 100m² surface to a 180m² one, offering more room for the existing team, and room to expand the team in the coming years. As of January 1, 2019, we have a team of 8 engineers working in Toulouse.
  • We moved our office in Lyon end of 2018 from a small one room office of 30m² to a full office of 100m², here as well to expand the team in the coming years. As of January 1, 2019, the team in Lyon has 2 engineers, but we hope to increase this number soon (see Recruiting below).


In terms of recruiting:

  • Maxime Chevallier joined us in February 2018, and has since then been mostly working on networking topics on Marvell platforms, but also a few other engineering projects.
  • Paul Kocialkowski joined us in March 2018 for an internship focused on the Allwinner VPU development and then was hired as a full-time engineer starting November 2018.
  • Thanks to our office expansion in Lyon, we have an open position for a Embedded Linux and Kernel engineer with existing experience in Lyon. See our blog post (in French) for more details.
  • We have openings for several internships in 2019, on Linux, U-Boot, Buildroot and Elixir related topics. See our blog post (in French).

Financial support

In 2018, we continued to support organizations and events who promote and defend Free Software:

  • Donating 1,024 EUR to Framasoft, an organization whose goal (in addition to supporting Free Software) is to decentralize Internet services. For example, they made a huge effort to release PeerTube in 2018, a peer-to-peer and of course Free Software alternative to centralized video hosting solutions.
  • Donating 1,024 EUR to Wikimedia France, to support free knowledge sharing through projects such as Wikipedia and Wikimedia Commons.
  • Donating 1,024 EUR to April, a French organization doing terrific work to promote Free Software, to follow the evolution of national and European law, and to animate campaigns to keep our political representatives aware of the needs of Free Software developers and users.
  • We also sponsored the Capitole du Libre 2018 (250 EUR) and Buildroot Developers Meeting 2018 in Edinburgh (250 EUR) events.
  • And of course, we support the LWN.net on-line weekly column through a corporate subscription (810 USD).
  • Last words

    We have plenty of ideas for 2019, so stay tuned for more news. We hope that 2019 will be a great year for you too, with many contributions of all kinds to the lives of others.

    A year of Bootlin contributions to U-Boot

    We regularly post about Bootlin contributions to the Linux kernel, but we more rarely post about our U-Boot contributions. Even though we are a bit less active in U-Boot than we are in Linux, we do quite a bit of upstream U-Boot work as well. In this blog post, we do a review of our most significant U-Boot contributions in 2018.

    U-Boot 2018.03

    Maxime Ripard contributed support for using multiple U-Boot environments. Thanks to this, multiple U-Boot environment backends can be compiled into a single U-Boot binary, so that it can support falling back to a different environment backend if needed. For example, U-Boot can try to load an environment from a file in a FAT partition, and if that fails, try to load from raw MMC storage. As explained by Maxime Ripard in his cover letter, this is useful to help converting Allwinner-based platforms from an environment stored in raw MMC to an environment stored in a FAT partition.

    U-Boot 2018.05

    Miquèl Raynal contributed support for the Allwinner A33 based Nintendo NES Classic platform. It was also the first Allwinner A33 platform supported in U-Boot that boots from NAND, so as part of this work, Miquèl had to change the Allwinner NAND driver used in the SPL to make it work on Allwinner A31, which required using PIO transfers instead of DMA, and a number of other changes.

    U-Boot 2018.07

    Miquèl Raynal contributed generic support for TPMv2, and also specifically support for TPMv2 chips over SPI. We will publish a more detailed blog post about this topic in the near future.

    U-Boot 2018.09

    Quentin Schulz improved the env import command so that it can filter the environment variables it loads from the provided environment. This allows to white-list only a few selected environment variables in cases where the system is locked down by secure boot, but we still need a small writable U-Boot environment to store a few variables. As part of this release, Miquèl Raynal also contributed a few TPM-related fixes.

    U-Boot 2018.11

    • Miquèl Raynal contributed a lot of changes in the MTD subsystem, which brought support for SPI NAND flash memories in U-Boot. We described this work in a previous blog post. Boris Brezillon helped by submitting a number of fixes related to this effort.
    • Miquèl Raynal contributed a new mtd command, which can be used in a generic way to access all flash memories. This command will replace commands such as sf, nand, etc. We will publish in the near future a separate blog post about this topic.
    • Quentin Schulz contributed a SPI controller driver for the ARM PL022 SPI controller, which we are using on an old STMicro SPEAr600 platform.
    • Maxime Ripard contributed a brand new subsystem to support One Wire devices. This work was initially started by Maxime years ago as part of our work on the CHIP platform from Nextthing, and was picked up by Eugen Hristev from Microchip who pushed it all the way to upstream U-Boot.

    U-Boot 2019.01

    • Grégory Clement contributed the support for the Microchip/Microsemi Ocelot and Luton MIPS platforms, which includes the core code, but also a GPIO driver and a pinctrl driver.
    • Boris Brezillon contributed a number of fixes in the MTD subsystem to address various issues introduced by our work on this subsystem in the previous release.
    • Quentin Schulz contributed support for the VSC8574 and VSC8584 Ethernet PHYs from Microchip/Microsemi.
    • Miquèl Raynal improved the NAND controller driver for Marvell platforms by adding raw read support, which was used to add support for NAND chips using 2 KB pages and a ECC strength of 8 bits.

    Overall contribution statistics

    Overall, during this year, Bootlin engineer Miquèl Raynal contributed 90 commits, Maxime Ripard 33 commits, Boris Brezillon 24 commits, Quentin Schulz 14 commits, Grégory Clement 9 commits and Mylène Josserand 2 commits, a total of 172 commits, including some significant new features: SPI NAND support, TPMv2 support, One Wire subsystem, Ocelot and Luton platform support, ARM PL022 SPI controller support, support for additional Ethernet PHY, support for multiple environments.

    We expect to continue our involvement in upstream U-Boot development, starting with a new network driver for the Microchip/Microsemi Ocelot and Luton platforms.

    Detailed list of our contributions

    Allwinner VPU support in mainline Linux end of the year status update

    The end of 2018 is approaching, which is the right time to provide an update on where we stand with the Allwinner VPU support in Linux. The promise of our Kickstarter campaign was to deliver all funded stretch goals by the end of 2018. As we’ll explain below, all the goals have been met, and only the upstreaming process is not completely finished for some features.

    With the Linux 4.20 release happening just a few days ago, the core of the Cedrus driver and the media Requests API that supports it are finally available through Linus Torvalds’ tree! They provide the required interface for hardware-accelerated MPEG-2 decoding on the A13, A20, A33 and H3 Allwinner SoCs.

    Cedrus driver in staging

    Discussions regarding the details of the stateless video decoding interface offered by the V4L2 API are still taking place, which explains why our driver was integrated as a staging media driver. It was also decided to hide the associated interface for MPEG-2 decoding from the public kernel headers for now. This way, the interface is not considered stable and can keep evolving as discussions are still taking place. Because the kernel has a policy of never breaking backward compatibility, these interfaces will hardly evolve once they are declared stable, so it is crucial to ensure they are ready when that happens. This is especially true given the level of complexity associated with video decoding and the various pitfalls paving that road.

    Status of H264 and H265 decoding support

    The code for H264 and H265 decoding is already developed and functional, has already been submitted for upstream inclusion but it hasn’t been merged yet. However, with the decoding interfaces considered unstable for now, it should become easier to bring-in H.264 and H.265 decoding support to mainline. Support for these two codecs in the API and our driver is still under review and we will continue sending new iterations for them, with the suggested changes and fixes as well as adaptations for the still-evolving decoding interface. More specifically, our series need to be updated to the latest proposal for identifying reference frames, which is now based on the timestamps of the buffers.

    Platform support: H5, A64 and A10 on the horizon

    Regarding the platforms supported by our driver, the patches for H5 and A64 support were accepted since our last update and they will make it to Linux 4.21! We are also looking to send out support for the A10, which was missing from our previous series (but shouldn’t cause any particular trouble).

    DRM driver improvements

    The adaptations for the DRM driver allowing to display the raw decoded frames from the VPU on older platforms were also finalized, with the first half of the series already queued for 4.21. Subsequent changes in the series are still waiting for more reviews as they affect common parts of the framework.


    Overall, we are slowly closing down on this project and hoping to get the remaining pieces of our work integrated in mainline Linux as soon as possible, as there seems to be very few obstacles left in the way.

    Linux 4.20 released, Bootlin contributions

    Penguin from Mylène Josserand
    Drawing from Mylène Josserand, based on a picture from Samuel Blanc (https://commons.wikimedia.org/wiki/File:Manchot_royal_-_King_Penguin.jpg)
    The Linux 4.20 kernel has been released just before Christmas, on December 23. As usual, LWN had a very nice coverage of the most significant features and improvements provided by this new release as part of the merge window articles: part 1 and part 2.

    Bootlin once again contributed to this Linux 4.20 release, with a total of 216 non-merge commits, which puts us the 13th contributing company by number of commits and the 8th contributing company by number of lines changed, according to LWN statistics for the 4.20 release.

    Significant Bootlin contributions

    For Linux 4.20, the most significant contributions from Bootlin have been:

    • On the support for Marvell platforms
      • Antoine Ténart reworked how the “software thread” mechanism is handled in the mvpp2 network driver, used on Marvell Armada 375 and 7K/8K.
      • Maxime Chevallier enabled XPS support in the same mvpp2 driver
      • Maxime Chevallier added logic to support 2.5G speed in the mvneta driver, but this logic is not enabled yet, as we don’t have the necessary COMPHY driver for Armada 38x to really allow using 2.5G speed.
      • Miquèl Raynal added suspend/resume support for the Armada 37xx clock driver. This is part of a larger work to enable suspend/resume on the Armada 37xx platform.
      • Miquèl Raynal improved the Marvell ICU driver to support SEI interrupts. The ICU is the Interrupt Collector Unit, found on Marvell Armada 7K/8K. It turns wired interrupts from a part of the chip called the “Communication Processor” (CP) into message interrupts so that they can be notified to the other part of the chip called the “Application Processor” (AP), which contains the CPU core and GIC.
      • Thomas Petazzoni introduced some common code in the PCI subsystem to emulate a PCI root port bridge, and converted the pci-mvebu and pci-aardvark drivers to use it. pci-mvebu already had such an emulation logic, but since it became also needed for pci-aardvark, we turn it into a piece of common code so that it can be shared by both drivers (and perhaps others in the future). pci-mvebu is used on Marvell Armada XP, 370, 375, 38x, while pci-aardvark is used on Marvell Armada 37xx.
    • On the support for Allwinner platforms
      • Paul Kocialkowski contributed the Cedrus VPU driver, with for now just MPEG2 decoding support. This work was done thanks to the successful crowd-funding campaign we did in February/March 2018.
      • Paul Kocialkowski contributed a few fixes to the sun4i DRM display driver.
    • On the support for Microchip/Microsemi MIPS platforms
      • Alexandre Belloni added support for the Microsemi Jaguar2 in the Designware SPI controller driver
      • Alexandre Belloni added support for the Microsemi Ocelot in the Designware I2C controller driver
      • Quentin Schulz contributed a new driver in the PHY subsystem to configure the SERDES muxing on Microsemi Ocelot platforms
      • Quentin Schulz contributed a new Device Tree description for the Microsemi Ocelot PCB120 platform
    • On the support Microchip/Atmel ARM platforms
      • Alexandre Belloni got the first step of the clock drivers rework merged. The purpose of this rework is to move from a Device Tree representation with one Device Tree node per clock to a much simpler representation with only one Device Tree node for the whole clock controller. The SAMA5D2, SAMA5D4, AT91SAM9260, AT91SAM9x5 at AT91SAM9RL clock drivers have already been converted. Other platforms and DT changes will arrive in future releases.
    • In the support for RaspberryPi platforms
      • Boris Brezillon contributed a few minor fixes for the vc4 DRM driver.
    • In the RTC subsystem
      • As the subsystem maintainer, Alexandre Belloni as usual did a number of cleanups and improvements in numerous drivers, especially to use more modern APIs where possible.
    • In the network subsystem
      • Quentin Schulz contributed extensive support for the Microsemi VSC8574 and VSC8584 Ethernet PHYs.
    • In the MTD subsystem
      • Subsystem maintainer Boris Brezillon did a lot of changes to pass a nand_chip object to numerous NAND subsystem hooks, and fixed all the drivers accordingly.
      • Boris Brezillon also deprecated a significant number of NAND subsystem hooks, by introducing a nand_legacy structure with legacy hooks. This should encourage developers to move their drivers to the more modern MTD/NAND APIs.

    Bootlin maintainers activity

    A number of Bootlin engineers are maintainers in the Linux kernel, so their work is not visible as patch authors, but rather as developers reviewing and merging patches contributed by others. As part of this maintainer work:

    • Maxime Ripard reviewed and merged 47 patches from other developers, as the Allwinner platform co-maintainer
    • Boris Brezillon reviewed and merged 36 patches from other developers, as the MTD subsystem co-maintainer
    • Alexandre Belloni reviewed and merged 64 patches from other developers, as the RTC subsystem maintainer and the Microchip/Atmel platform co-maintainer
    • Grégory Clement reviewed and merged 25 patches from other developers, as the Marvell platform co-maintainer
    • Miquèl Raynal reviewed and merged 71 patches from other developers, as the NAND subsystem co-maintainer

    Detailed list of Bootlin contributions

    MIPI I3C support is now in upstream Linux

    MIPI I3C specification publishedBack in August 2017, we wrote in a blog post about the first iteration of the Linux kernel subsystem we proposed to support the brand new MIPI I3C bus. Almost a year and half later, there are some really good news:

    • The Linux I3C support now has its own Git repository on kernel.org
    • The Linux I3C community has its mailing list.
    • Besides the first I3C controller driver we wrote for the Cadence I3C Master, Synopsys has contributed a second driver for their I3C master IP: i3c: master: Add driver for Synopsys DesignWare IP. This definitely helped show that there is interest in I3C beyond our contributions, and also helped validate that the subsystem was working fine for a different I3C controller.
    • The Linux I3C tree has been part of linux-next since November 6, 2018: linux-next: Tree for Nov 6.
    • The Linux I3C subsystem has received a Reviewed-by: Arnd Bergmann and later on a Acked-by: Greg Kroah-Hartman, which were two key approvals to move forward with the merging of I3C support.
    • I3C subsystem maintainer Boris Brezillon has therefore sent a pull request to get this subsystem merged in the upcoming 4.21 (or 5.0 ?) Linux kernel: [GIT PULL] i3c: Initial pull request, and this pull request has been merged by Linus Torvalds, so the I3C subsystem is now visible in Linus Git tree: drivers/i3c. The merge commit has been done on December 25, so it arrived as a very nice Christmas present!

    It has been a long process, but we are proud and happy to have pioneered the support for I3C in the Linux kernel, from the design of the subsystem based on the I3C specifications all the way to its merging in the upstream Linux kernel and the creation of a small (but hopefully growing) community of developers around it.

    Real-Time Summit 2018

    This year, Bootlin engineer Maxime Chevallier attended the Real-Time Summit, which took place after ELCE in Edinburgh. In a similar fashion to the Linux Media Summit, this was a 1-day conference dedicated to Real-Time topics in the Linux ecosystem, more specifically the Linux Kernel.

    The future of Preempt-RT

    Real-Time (or should we say, deterministic) behavior in the Linux kernel has been pursued for a long time, the most famous effort being the Preempt-RT patch. As Steven Rostedt announced during his talk at ELCE 2018, the Preempt-RT patch is close to being fully merged in mainline Linux, we can expect to see this happen in 2019.

    Some of the maintainers of the Preempt-RT patch were present at the Real-Time summit, including Thomas Gleixner who lead the discussion throughout the day.

    This was the occasion to discuss the remaining points to be addressed for Preempt-RT to make it into mainline Linux :

    • Printk : As Steven Rostedt explained at ELCE 2017, printk is not very real-time friendly. The main issue was worked around, but John Ogness presented his current work of fully redesigning printk’s behaviour.
    • Thomas Gleixner talked about the current state of softirq handling, which is also a critical point for determinism. They work by “stealing” some irq context time, falling back to ksoftirqd when necessary. This is particularly problematic for networking drivers that heavily rely on softirq.
    • Peter Zijlstra exposed the different scheduler related issues that needs to be addressed, focusing on SCHED_DEADLINE.

    Modeling and analyzing the kernel behavior

    All the talks weren’t about the Preempt-RT match merging effort. Daniel Bristot de Oliveira presented his ongoing academic work on modeling the Linux task model. The idea here is to build a formal model that doesn’t take shortcuts or idealize the way tasks are handled in the kernel, so that this can be used as a basis for academic research on topics such as scheduling.

    One of the main arguments is that there’s a gap in terms of language and methodology used between kernel developers and the academic world. Daniel explained how he managed to build a huge state-machine representing the task model, and how he uses it now to verify that tasks behave how they should by running trace events in the state machine.

    This talk sparked a lot if interesting discussions, for example Peter Zijlstra suggested to compile the state machine into eBPF code and run it live in the kernel.

    Julia Lawall was present in the room, and improvised a talk inspired by Daniel’s presentation. She presented DSAC, a static analysis tool dedicated to finding Sleeping in Atomic Context bugs. Julia is involved in the development and use of the coccinelle tool, and explained that it is quickly limited when trying to find that categories of bugs, where sleeping calls can be deeply nested in a call stack protected by spinlocks. Using LLVM, DSAC can analyze complex scenarios with multiple level of nesting and indirect calls to detect SAC bugs. After analyzing the v4.17 kernel sources for only a few hours, the tool was able to detect more than 1000 bugs, 220 of which were confirmed.

    The overall technical level of the different talks was high, leading to passionate discussions and suggestions on every topic that was brought during the day.

    Feedback from Bootlin at the Linux Plumbers Conference 2018

    The Linux Plumbers Conference (LPC) was held a few weeks ago in Vancouver, BC. As always there were several tracks where contributors gave a presentation of on-going or future work, and discussed it with the audience, on specific topics such as thermal, containers, real time, device tree and many more. For the first time at LPC a 2-day networking track took place. As we work on a diversity of networking projects at Bootlin we decided to attend.

    Networking track at LPC. Photo @linuxplumbers.

    The hot topic of the last couple of years in conferences in the network subsystem is XDP, so the conference was not exception. We saw a handful of talks and discussions about the on-going work and support of XDP within the kernel. XDP provides a programmable network data path (using eBPF) in the Linux kernel to process bare metal packets at the lowest point in the network stack. Packets are processed directly in the drivers’ Rx queues, before any allocation happen (such as socket buffers). Facebook is one well known heavy user of this technology (every packet toward Facebook is processed by XDP) and its engineers gave feedback about how they use XDP and the issues they faced. Other projects and companies are currently evaluating and starting to use XDP as well: we also saw presentations about XDP/eBPF in Open vSwitch, DPDK or kTLS.

    While XDP/eBPF was featured in most of the discussions, other interesting topics where brought up. Andrew Lunn gave a presentation about the current need to go beyond 1G copper PHYs for many Linux enabled embedded devices. This was very interesting for us as we used and worked on the technologies used within the Linux kernel to address this, such as Phylink and the SFP bus (we used those when enabling 10G interfaces in the Marvell MacchiatoBin board).

    Another presentation caught our attention as the topic was related to what we do at Bootlin. Jesse Brandeburg from Intel talked about the networking hardware offloads and their APIs. He exposed a brief history of the offloads supported by NICs and then showed some issues with the current APIs, where some use cases or behaviors are not clearly defined and sometimes overlap. This is a feeling we share as we experienced it while implementing some of those hardware networking offloads. Jesse’s idea was to open a discussion to come up with better solutions within the next years, as NICs offloading continue to grow.

    The Linux Plumbers Conference was very pleasant and well organized. We had the chance to attend the networking track, seeing lots of great cutting-edge topics being discussed; as well as other interesting tracks.

    We’d like to thank the conference and track organizers, we had a great time! Videos, slides and papers are now available on the official website or on Youtube.

    Buildroot 2018.11 released, Bootlin contributions inside

    Buildroot logoThe 2018.11 release of Buildroot was published a few days ago. As is well-known, Bootlin is a strong contributor to this project, and this blog post proposes a summary of the new features provided by 2018.11, and highlights the contributions made by Bootlin.

    What’s new in 2018.11 ?

    • From a CPU architecture support point of view, by far the most important addition is support for the RISC-V 64 architecture. For now, only the 64-bit version of the architecture is supported, but the patches for the 32-bit version have been posted already, and will hopefully be merged for the next release. It is worth mentioning that we have already used the RISC-V 64 support in Buildroot to provide a pre-built toolchain for this architecture on our toolchains.bootlin.com site.
    • In the toolchain support area, the most important change is that glibc was upgraded to version 2.28. This caused a number of build issues with various packages, which were detected by the project autobuilders and fixed. musl was bumped to version 1.1.20, and the ARM (formerly Linaro) pre-built toolchains for ARM and AArch64 were updated.
    • The support for hardening flags, i.e flags passed to gcc to improve the “security” of programs, has been changed, and is now done directly as part of the compiler wrapper that Buildroot has. Indeed, when using Buildroot, arm-linux-gcc is not directly the usual gcc compiler, but a small wrapper program that Buildroot uses to make sure we always pass the appropriate flags when calling the cross-compiler. Passing those hardening flags through the wrapper allowed to solve a number of build issues. Options such as BR2_RELRO_PARTIAL, BR2_RELRO_FULL, BR2_SSP_REGULAR, BR2_SSP_STRONG and BR2_SSP_ALL should therefore work better now.
    • In terms of filesystem images, while Buildroot already supports the most popular filesystem types, two additional filesystems are now supported: btrfs and f2fs.
    • A number of new default configuration for various boards have been added: Amarula a64-relic, Bananapi m2 ultra, Embest riotboard, Hardkernel Odroid XU-4, QEMU riscv64-virt.
    • A number of packages have been added: bird, bluez5_utils-headers, btrfs-progs, checksec, davici, duktape, ell, haproxy, libclc, libcorrect, libopencl, libopenresolv, nss-myhostname, riscv-pk, sedutil, spandsp, tini, waffle, xapian, not counting the dozens of new Perl and Python modules that have been added.

    Bootlin contributions

    By far and large, the most significant contribution from Bootlin to Buildroot is the activity of Thomas Petazzoni as a co-maintainer for the project. Out of the 1366 commits made between the 2018.08 and 2018.11 release, Thomas authored 126 commits, but more importantly reviewed and merged 883 patches from other developers, or in other words 64% of the commits that have been made.

    As part of the 127 commits Bootlin contributed, we:

    • Fixed a large number of build issues reported by the autobuilder, or by the CI testing the build of our defconfigs.
    • Introduced a make check-package target to more easily use Buildroot check-package tool to verify the coding style of packages.
    • Updated the musl C library to 1.1.20.
    • Updated the Solidrun MacchiatoBin defconfigs (board powered by a Marvell Armada 8K processor) to use the most recent kernel, U-Boot and ATF versions.
    • Started adding a virtual package for opencl.
    • Fixed a number of missing dependencies on host-pkgconf (i.e pkg-config) which were detected by our work on per-package directories, that we will discuss in a future blog post.

    Here is the detailed list of our contributions to this release:

    Bootlin at the Linux Media Summit 2018

    This year’s edition of the Linux Media Summit happened a month ago, in Edinburgh, right after the Embedded Linux Conference. Since we were already at the ELCE, and that we’ve been more and more involved in the media community thanks to our work on the Allwinner CSI driver and more importantly the Cedrus driver, it was natural for us to attend.

    The media summit is usually a meeting to discuss the hot topics, so the whole day was a mix and match of various status updates and discussions on the future needs and developments around the Video4Linux2 framework.

    Linux Media Summit attendees

    Most of the discussion was about how to improve the contributor’s experience and improve the maintenance. The DRM subsystem was used as an example, since the number of patches are in the same order of magnitude, and a number of v4l2 contributors are also contributing to DRM drivers. Part of the improvement of both the maintenance and contribution experience will also come through some CI work, so there was a lot of discussions on how to improve the already existing tools (such as v4l2-compliance) but also how to setup some automatic tooling to run those tests as early as possible.

    A good part of the day was also spent on dealing with the current developments, such as the Request API we’ve used in the Cedrus driver, and how to integrate that API into popular multimedia frameworks like gstreamer or ffmpeg. It looks like our libva implementation was well received, so it will probably be made standard and hosted on linuxtv.org in the near future. Other developments discussed were fault tolerant v4l2, in order to deal with video pipelines where one or several components might not work anymore, and storing the v4l2 controls state in a persistent way.

    It was overall a very productive day, and it’s always nice to meet people you interact with over mailing list and IRC on a regular basis. If you want more information, you can read the extensive report.

    Bootlin adds SPI NAND support to U-Boot

    Bootlin is proud to announce that it has contributed SPI NAND support to the U-Boot bootloader, which is part of the recently released U-Boot 2018.11. Thanks to this effort, one can now use SPI NAND memories from U-Boot, a feature that had been missing for a long time.

    State of the art: Linux support

    A few months ago, Bootlin engineer Boris Brezillon added SPI-NAND support in the Linux kernel, based on an initial contribution from Peter Pan. As Boris explained in a previous blog post, adding SPI NAND support in Linux required adding a new spi-mem layer, that allows SPI NOR and SPI NAND drivers to leverage regular SPI controller drivers, but also to allow those SPI controller drivers to expose optimized operations for flash memory access. The spi-mem layer was added to the SPI subsystem by a first series of patches, while the SPI NAND support itself was added to the MTD subsystem as part of another patch series.

    The spi-mem framework in Linux
    The spi-mem framework in Linux

    Moving to U-Boot

    Since accessing flash memories from the bootloader is often necessary, Bootlin engineer Miquèl Raynal took the challenge of adding SPI NAND support in U-Boot. Miquèl did this by porting the SPI-mem and SPI-NAND subsystems from Linux to U-Boot. The first challenge when porting the SPI-mem and SPI-NAND code from Linux to U-Boot was that the U-Boot MTD stack hadn’t been synchronized with the one of Linux for quite some time. Thus a number of changes in the Linux MTD subsystem had to be ported to U-Boot as well, which was a fairly time-consuming effort. The SPI NAND code has been imported in drivers/mtd/nand/spi, while the spi-mem layer is in drivers/spi/spi-mem.c.

    Once the core code was ready, we had to find a way to let the user interact with the SPI NAND devices. Until now, U-Boot had a separate set of commands for each type of flash memory (nand for parallel NAND, erase/cp for parallel NOR, sf for SPI NOR), and it indeed seemed like adding yet another command was the way to go. Instead, we introduced a new mtd that can be used to access all flash memory devices, regardless of their specific type. We will discuss this mtd in more details in another blog post.

    However, such a move to a generic mtd command forced us to do a lot more cleanup than expected, as we ended up reworking the MTD partition handling, and even making deep changes in the ubi command. This was more complicated than anticipated because of the SPI NOR support in U-Boot: it is not very well integrated with MTD subsystem, in the sense that there is a duplication of information between the SPI NOR and MTD subsystems, and when the duplicated information is no longer consistent, really bad things happen. As an example, any call to sf probe was doing a reset of the MTD device structure using memset, causing all other state information contained in this structure to be lost. Since the SPI NAND support relies on the MTD subsystem (much more than the current SPI NOR support), we had to mitigate those issues. Long term, a proper rework of the SPI NOR support in U-Boot is definitely needed.

    Some of those issues are present in the 2018.11 release and were discovered by U-Boot users who started testing the new mtd command. We have contributed a patch series addressing them, which hopefully should be merged soon.

    Now that those difficulties are hopefully behind us, the U-Boot SPI-NAND support looks pretty stable, and we have quite a few SPI-NAND manufacturer drivers in U-Boot mainline, with Gigadevice, Macronix, Micron and Winbond supported so far. We’re happy to have contributed this new significant feature, as it finally allows to use this popular type of flash memory in U-Boot.