Seminar “Porting Linux on an ARM board”, materials available

Porting Linux on an ARM boardOn December 10th 2015, Bootlin engineer Alexandre Belloni gave a half-day seminar on the topic of Porting Linux on an ARM board in Toulouse, France. This seminar covers topics like porting the bootloader, understanding the concept of the Device Tree, writing Linux device drivers and more. With ~50 persons from various companies attending and lots of questions from the audience, this first edition has been very successful, which shows an increasing interest for using Linux on ARM platforms in the industry.

We are now publishing the 220 slides materials from this seminar, available in PDF format. Like all our training materials, this material is published under the Creative Commons BY-SA 3.0 license, which allows everyone to re-use it for free, provided the derivative works are released under the same license. We indeed re-used quite extensively parts of our existing training materials for this half-day seminar.

We plan to give this half-day seminar in other locations in France in 2016. Contact us if you are interested in organizing a similar seminar in your area (we are happy to travel!).

Device Tree on ARM article in French OpenSilicium magazine

Our French readers are most likely aware of the existence of a magazine called OpenSilicium, a magazine dedicated to embedded technologies, with frequent articles on platforms like the Raspberry Pi, the BeagleBone Black, topics like real-time, FPGA, Android and many others.

Open Silicium #17

Issue #17 of the magazine has been published recently, and features a 14-pages long article Introduction to the Device Tree on ARM, written by Bootlin engineer Thomas Petazzoni.

Open Silicium #17

Besides Thomas article, many other topics are covered in this issue:

  • A summary of the Embedded Linux Conference Europe 2015 in Dublin
  • Icestorm, a free development toolset for FPGA
  • Using the Armadeus APF27 board with Yocto
  • Set up an embedded Linux system on the Zynq ZedBoard
  • Debugging with OpenOCD and JTAG
  • Usage of the mbed SDK on a small microcontroller, the LPC810
  • From Javascript to VHDL, the art of writing synthetizable code using an imperative language
  • Optimization of the 3R strems decompression algorithm

Bootlin at FOSDEM and the Buildroot Developers Meeting

FOSDEM 2016The FOSDEM conference will take place on January 30-31 in Brussels, Belgium. Like every year, there are lots of interesting talks for embedded developers, starting from the Embedded, Mobile and Automotive Devroom, but also the Hardware track, the Graphics track. Some talks of the IoT and Security devrooms may also be interesting to embedded developers.

Thomas Petazzoni, embedded Linux engineer and CTO at Bootlin, will be present during the FOSDEM conference. Thomas will also participate to the Buildroot Developers Meeting that will take place on February 1-2 in Brussels, hosted by Google.

Linux 4.4, Bootlin contributions

Linux 4.4 is the latest releaseLinux 4.4 has been released, a week later than the normal schedule in order to allow kernel developers to recover from the Christmas/New Year period. As usual, LWN has covered the 4.4 cycle merge window, in two articles: part 1 and part 2. This time around, KernelNewbies has a nice overview of the Linux 4.4 changes. With 112 patches merged, we are the 20th contributing company by number of patches according to the statistics.

Besides our contributions in terms of patches, some of our engineers have also become over time maintainers of specific areas of the Linux kernel. Recently, LWN.net conducted a study of how the patches merged in 4.4 went into the kernel, which shows the chain of maintainers who pushed the patches up to Linus Torvalds. Bootlin engineers had the following role in this chain of maintainers:

  • As a co-maintainer of the Allwinner (sunxi) ARM support, Maxime Ripard has submitted a pull request with one patch to the clock maintainers, and pull requests with a total of 124 patches to the ARM SoC maintainers.
  • As a maintainer of the RTC subsystem, Alexandre Belloni has submitted pull requests with 30 patches directly to Linus Torvalds.
  • As a co-maintainer of the AT91 ARM support, Alexandre Belloni has submitted pull requests with 46 patches to the ARM SoC maintainers.
  • As a co-maintainer of the Marvell EBU ARM support, Gregory Clement has submitted pull requests with a total of 33 patches to the ARM SoC maintainers.

Our contributions for the 4.4 kernel were centered around the following topics:

  • Alexandre Belloni continued some general improvements to support for the AT91 ARM processors, with fixes and cleanups in the at91-reset, at91-poweroff, at91_udc, atmel-st, at91_can drivers and some clock driver improvements.
  • Alexandre Belloni also wrote a driver for the RV8803 RTC from Microcrystal.
  • Antoine Ténart added PWM support for the Marvell Berlin platform and enabled the use of cpufreq on this platform.
  • Antoine Ténart did some improvements in the pxa3xx_nand driver, still in preparation to the addition of support for the Marvell Berlin NAND controller.
  • Boris Brezillon did a number of improvements to the sunxi_nand driver, used for the NAND controller found on the Allwinner SoCs. Boris also merged a few patches doing cleanups and improvements to the MTD subsystem itself.
  • Boris Brezillon enabled the cryptographic accelerator on more Marvell EBU platforms by submitting the corresponding Device Tree descriptions, and he also fixed a few bugs found in the driver
  • Maxime Ripard reworked the interrupt handling of per-CPU interrupts on Marvell EBU platforms especially in the mvneta network driver. This was done in preparation to enable RSS support in the mvneta driver.
  • Maxime Ripard added support for the Allwinner R8 and the popular C.H.I.P platform.
  • Maxime Ripard enabled audio support on a number of Allwinner platforms, by adding the necessary clock code and Device Tree descriptions, and also several fixes/improvements to the ALSA driver.

The details of our contributions for 4.4:

Linux 4.3 released, Bootlin contributions inside

Adelie PenguinThe 4.3 kernel release has been released just a few days ago. For details about the big new features in this release, we as usual recommend to read LWN.net articles covering the merge window: part 1, part 2 and part 3.

According to the KPS statistics, there were 12128 commits in this release, and with 110 patches, Bootlin is the 20th contributing company. As usual, we did some contributions to this release, though a somewhat smaller number than for previous releases.

Our main contributions this time around:

  • On the support for Atmel ARM SoCs
    • Alexandre Belloni contributed a fairly significant number of cleanups: description of the slow clock in the Device Tree, removal of left-over from platform-data usage in device drivers (no longer needed now that all Atmel ARM platforms use the Device Tree).
    • Boris Brezillon contributed numerous improvements to the atmel-hlcdc, which is the DRM/KMS driver for the modern Atmel ARM SoCs. He added support for several SoCs to the driver (SAMA5D2, SAMA5D4, SAM9x5 and SAM9n12), added PRIME support, and support for the RGB565 and RGB444 output configurations.
    • Maxime Ripard improved the dmaengine drivers for Atmel ARM SoCs (at_hdmac and at_xdmac) to add memset and scatter-gather memset capabilities.
  • On the support for Allwinner ARM SoCs
    • Maxime Ripard converted the SID driver to the newly introduced nvmem framework. Maxime also did some minor pin-muxing and clock related updates.
    • Boris Brezillon fixed some issues in the NAND controller driver.
  • On the support for Marvell EBU ARM SoCs
    • Thomas Petazzoni added the initial support for suspend to RAM on Armada 38x platforms. The support is not fully enabled yet due to remaining stability issues, but most of the code is in place. Thomas also did some minor updates/fixes to the XOR and crypto drivers.
    • Grégory Clement added the initial support for standby, a mode that allows to forcefully put the CPUs in deep-idle mode. For now, it is not different from what cpuidle provides, but in the future, we will progressively enable this mode to shutdown PHY and SERDES lanes to save more power.
  • On the RTC subsystem, Alexandre Belloni did numerous fixes and cleanups to the rx8025 driver, and also a few to the at91sam9 and at91rm9200 drivers.
  • On the common clock framework, Boris Brezillon contributed a change to the ->determinate_rate() operation to fix overflow issues.
  • On the PWM subsystem, Boris Brezillon contributed a number of small improvements/cleanups to the subsystem and some drivers: addition of a pwm_is_enabled() helper, migrate drivers to use the existing helper functions when possible, etc.

The detailed list of our contributions is:

Bootlin at the Linux Kernel Summit 2015

Kernel Summit 2012 in San DiegoThe Linux Kernel Summit is, as Wikipedia says, an annual gathering of the top Linux kernel developers, and is an invitation-only event.

In 2012 and 2013, several Bootlin engineers have been invited and participated to a sub-event of the Linux Kernel Summit, the “ARM mini-kernel summit”, which was more specifically focused on ARM related developments in the kernel. Gregory Clement and Thomas Petazzoni went to the event in 2012 in San Diego (United States) and in 2013, Maxime Ripard, Gregory Clement, Alexandre Belloni and Thomas Petazzoni participated to the ARM mini-kernel summit in Edinburgh (UK).

This year, Thomas Petazzoni has been invited to the Linux Kernel Summit, which will take place late October in Seoul (South Korea). We’re happy to see that our continuous contributions to the Linux Kernel are recognized and allow us to participate to such an invitation-only event. For us, participating to the Linux Kernel Summit is an excellent way of keeping up-to-date with the latest Linux kernel developments, and also where needed, give our feedback from our experience working in the embedded industry with several SoC, board and system vendors.

Linux 4.2 released, Bootlin contributions inside

Adelie Penguin
Linus Torvalds has released last sunday the 4.2 release of the Linux kernel. LWN.net covered the merge window of this 4.2 release cycle in 3 parts (part 1, part 2 and part 3), giving a lot of details about the new features and important changes.

In a more recent article, LWN.net published some statistics about the 4.2 development cycle. In those statistics, Bootlin appears as the 10th contributing company by number of patches with 203 patches integrated, and Bootlin engineer Maxime Ripard is in the list of most active developers by changed lines, with 6000+ lines changed. See also this page for more kernel contribution statistics.

This time around, the most important contributions of Bootlin where:

  • Support for Atmel ARM processors:
    • The effort to clean-up the arch/arm/mach-at91/ continued, now that the conversion to the Device Tree and multiplatform is completed. This was mainly done by Alexandre Belloni.
    • Support for the ACME Systems Arietta G25 was added by Alexandre Belloni.
    • Support for the RTC on at91sam9rlek was also added by Alexandre Belloni.
    • Significant improvements were brought to the dmaengine xdmac and hdmac drivers (used on Atmel SAMA5D3 and SAMA5D4), bringing interleaved support, memset support, and better performance for certain use cases. This was done by Maxime Ripard.
  • Support for Marvell Berlin ARM processors:
    • In preparation to the addition of a driver for the ADC, an important refactoring of the reset, clock and pinctrl driver was done by using a regmap and the syscon mechanism to more easily share the common registers used by those drivers. Worked done by Antoine Ténart.
    • An IIO driver for the ADC was contributed, which relies on the syscon and regmap mentioned above, as the ADC uses registers that are mixed with the clock, reset and pinctrl ones.
    • The Device Tree files were relicensed under GPLv2 and X11 licenses.
  • Support for Marvell EBU ARM processors:
    • A completely new driver for the CESA cryptographic engine was contributed by Boris Brezillon. This driver aims at replacing the old mv_cesa drivers, by supporting the newer features of the cryptographic engine available in recent Marvell EBU SoCs (DMA, new ciphers, etc.). The driver is backward compatible with the older processors, so it will be a full replacement for mv_cesa.
    • A big cleanup/verification work was done on the pinctrl drivers for Armada 370, 375, 38x, 39x and XP, leading to a number of fixes to pin definitions. This was done by Thomas Petazzoni.
    • Various fixes were made (suspend/resume improvements, big endian usage, SPI, etc.).
  • Support for the Allwinner ARM processors:
    • Support for the AXP22x PMIC was added by Boris Brezillon, including the support for the regulators provided by this PMIC. This PMIC is used on a significant number of Allwinner designs.
    • A small number of Device Tree files were relicensed under GPLv2 and X11 licenses.
    • A big cleanup of the Device Tree files was done by using more aggressively the “DT label based syntax”
    • A new driver, sunxi_sram, was added to support the SRAM memories available in some Allwinner processors.
  • RTC subsystem:
    • As was announced recently, Bootlin engineer Alexandre Belloni is now the co-maintainer of the RTC subsystem. He has set up a Git repository at https://git.kernel.org/cgit/linux/kernel/git/abelloni/linux.git/ to maintain this subsystem. During the 4.2 release cycle, 46 patches were merged in the drivers/rtc/ directory: 7 were authored by Alexandre, and all other patches (with the exception of two) were merged by Alexandre, and pushed to Linus.

The full details of our contributions:

Bootlin talks at the Embedded Linux Conference Europe

Father Mathew BridgeThe Embedded Linux Conference Europe 2015 will take place on October 5-7 in Dublin, Ireland. As usual, the entire Bootlin engineering team will participate to the event, as we believe it is one of the great way for our engineers to remain up-to-date with the latest embedded Linux developments and connect with other embedded Linux and kernel developers.

The conference schedule has been announced recently, and a number of talks given by Bootlin engineers have been accepted:

We submitted other talks that got rejected, probably since both of them had already been given at the Embedded Linux Conference in California: Maxime Ripard’s talk on dmaengine and Boris Brezillon’s talk on supporting MLC NAND (which we regret since Boris is currently actively working on this topic, so we are expecting to have some useful results by the time of ELCE, compared to his ELC talk which was mostly a presentation of the issues and some proposals to address them). Interested readers can anyway watch those talks and/or read the slides.

In addition to the Embedded Linux Conference Europe itself:

  • Thomas Petazzoni will participate to the Buildroot developers meeting on October 3/4, right before the conference.
  • Alexandre Belloni will participate to the OEDEM, the 2015 OpenEmbedded Developer’s European Meeting, taking place on October 9 after the conference.

Linux 4.1 released, Bootlin 17th contributing company

TuxLinus Torvalds recently released the 4.1 Linux kernel, for which LWN.net gave a good description of the major new features: 4.1 Merge window, part 1, 4.1 Merge window, part 2, The 4.1 merge window closes.

As usual, Bootlin engineers contributed to the Linux kernel during this development cycle, though this time with a smaller number of patches: we contributed 118 patches. This time around, Bootlin is the 17th company contributing to this kernel release, by number of patches.

Our major contributions this time around have been:

  • On support for Atmel platforms
    • Alexandre Belloni did a good number of improvements to Atmel SoC support: converting some remaining SoCs to the SoC detection infrastructure, cleaning up the timer driver to use a syscon/regmap, removing a lot of unused headers in arch/arm/mach-at91/, etc. The final and very important change is that the AT91 ARM platform is now part of the multiplatform mechanism: you can build a single zImage for ARMv5 or for ARMv7 which will include support for the ARMv5 or ARMv7 Atmel platforms.
    • Boris Brezillon improved the Atmel DRM/KMS driver for the display controller by switching to atomic mode-setting. He also added Device Tree definitions for the Atmel display controller on Atmel SAMA5D3 and Atmel SAMA5D4.
  • On support for Marvell EBU platforms
    • Ezequiel Garcia enabled the Performance Monitor Unit on Armada 375 and Armada 38x, which allows to use perf on those platforms.
    • Gregory Clement did a number of fixes and minor improvements to support for Marvell EBU platforms.
    • Maxime Ripard enabled the Performance Monitoring Unit on Armada 370/XP, enabling the use of perf on these platforms. He also improved support for the Armada 385 AP board by enabling NAND and USB3 support.
    • Thomas Petazzoni added initial support for the new Marvell Armada 39x platform (clock driver, pinctrl driver, Device Tree). He did some cleanup and fixes in many Device Tree of Marvell EBU platforms and added suspend/resume support in the PCI and pinctrl drivers for these platforms.
  • Other contributions
    • As we posted recently, Alexandre Belloni also became in this release cycle a co-maintainer for the RTC subsystem.
    • Alexandre Belloni added bq27510 support for the bq27x00_battery driver.
    • Maxime Ripard did some small contributions to the dmaengine subsystem, improved the of_touchscreen code and the edt-ft5x06 touchscreen driver, and did some cleanup in the Allwinner sun5i clocksource driver.

For the upcoming 4.2 version, we have 198 patches in linux-next, of which 191 have already been pulled by Linus as part of the 4.2 merge window.

Our complete list of contributions follows:

Buildroot 2015.05 release, Bootlin contributions inside

Buildroot LogoThe Buildroot project has recently released a new version, 2015.05. With exactly 1800 patches, it’s the largest release cycle ever, with patches from more than 100 different contributors. It’s an impressive number, showing the growing popularity of Buildroot as an embedded Linux build system.

The CHANGES file summarizes the most important improvements of this release.

Amongst those 1800 patches, 143 patches were contributed by Bootlin. Our most significant contributions for this release have been:

  • Addition of a package for the wf111 WiFi drivers. They allow to use a WiFi chip from Bluegiga, which is being used in one of our customer projects.
  • Addition of the support for using uClibc-ng. uClibc-ng is a “collaborative” fork of the uClibc project, which aims at doing more regular releases and have better testing. Maintained by Waldemar Brodkorb, the project has already seen several releases since its initial 1.0 release. Waldemar is merging patches from the original uClibc regularly, and adding more fixes. It allows Buildroot and other uClibc users to have well-identified uClibc stable versions instead of a 3 years old 0.9.33.2 version with dozens of patches on top of it. uClibc-ng is not currently used as the default uClibc version as of 2015.05, but it might very well be the case in 2015.08.
  • Important internal changes to the core infrastructure. Until this release, the make legal-info, make source, make external-deps and make source-check logic was relying only on the Buildroot configuration file. This was giving correct results for target packages which all have a corresponding Buildroot configuration option, but not for host packages (which for most of them don’t have Buildroot configuration options). Only a manual two-level dependency handling was done for the host packages for the above mentioned commands. With our work, the handling of those features has been moved to be part of the package infrastructure itself, so it’s using proper make recursivity to resolve the entire dependency tree. Due to this, the results of make legal-info or make external-deps may be longer following this release, but it’s because it’s now actually correct and complete. You can look at the patches for more details, but these changes are very deep into the core Buildroot infrastructure.
  • Large number of build fixes. We contributed 52 patches fixing issues detected by the autobuild infrastructure.
  • Addition of the imx-usb-loader package, which can be used to load over USB a new bootloader on i.MX6 platforms, even if the platform has no bootloader or a broken bootloader. We also use it as part of one of our customer projects.

With 142 patches, Bootlin engineer Thomas Petazzoni is the third contributor to this release by number of patches:

git shortlog -s -n 2015.02..

   397	Bernd Kuhls
   393	Gustavo Zacarias
   142	Thomas Petazzoni

But by far, our most important contribution by far for this release is Thomas acting as the interim maintainer: on the total of 1800 patches merged for this release, Thomas has been the committer of 1446 patches. He has therefore been very active in merging the patches contributed by the Buildroot community.

There are already some very interesting goals set for the Buildroot 2015.08 release, as you can see on the Buildroot release goals page.

Also, if you want to learn Buildroot in details, do not hesitate to look at our Buildroot training course!