Thomas Petazzoni is Bootlin's co-owner and CEO. Thomas joined Bootlin in 2008 as a kernel and embedded Linux engineer, became CTO in 2013, and co-owner/CEO in 2021. More details...
Bootlin engineers Quentin Schulz, Maxime Ripard and Miquèl Raynal will also be attending the event, which means that 7 people from Bootlin will participate to ELCE!
In addition to the main ELCE conference, Thomas Petazzoni will participate to the Buildroot Developers Days, a 2-day hackaton organized on Saturday and Sunday prior to ELCE, and will participate to the Device Tree workshop organized on Thursday afternoon.
Once again, we’re really happy to participate to this conference, and looking forward to meeting again with a large number of Linux kernel and embedded Linux developers!
This release gathers 13006 non-merge commits, amongst which 239 were made by Bootlin engineers. According to the LWN article on 4.13 statistics, this makes Bootlin the 13th contributing company by number of commits, the 10th by lines changed.
The most important contributions from Bootlin for this release have been:
In the RTC subsystem
Alexandre Belloni introduced a new method for registering RTC devices, with one step for the allocation, and one step for the registration itself, which allows to solve race conditions in a number of drivers.
Alexandre Belloni added support for exposing the non-volatile memory found in some RTC devices through the Linux kernel nvmem framework, making them usable from userspace. A few drivers were changed to use this new mechanism.
In the MTD/NAND subsystem
Boris Brezillon did a large number of fixes and minor improvements in the NAND subsystem, both in the core and in a few drivers.
Thomas Petazzoni contributed the support for on-die ECC, specifically with Micron NANDs. This allows to use the ECC calculation capabilities of the NAND chip itself, as opposed to using software ECC (calculated by the CPU) or ECC done by the NAND controller.
Thomas Petazzoni contributed a few improvements to the FSMC NAND driver, used on ST Spear platforms. The main improvement is to support the ->setup_data_interface() callback, which allows to configure optimal timings in the NAND controller.
Support for Allwinner ARM platforms
Alexandre Belloni improved the sun4i PWM driver to use the so-called atomic API and support hardware read out.
Antoine Ténart improved the sun4i-ss cryptographic engine driver to support the Allwinner A13 processor, in addition to the already supported A10.
Maxime Ripard contributed HDMI support for the Allwinner A10 processor (in the DRM subsystem) and a number of related changes to the Allwinner clock support.
Quentin Schulz improved the support for battery charging through the AXP20x PMIC, used on Allwinner platforms.
Support for Atmel ARM platforms
Alexandre Belloni added suspend/resume support for the Atmel SAMA5D2 clock driver. This is part of a larger effort to implement the backup mode for the SAMA5D2 processor.
Alexandre Belloni added suspend/resume support in the tcb_clksrc driver, used as for clocksource and clockevents on Atmel SAMA5D2.
Alexandre Belloni cleaned up a number of drivers, removing support for non-DT probing, which is possible now that the AVR32 architecture has been dropped. Indeed, the AVR32 processors used to share the same drivers as the Atmel ARM processors.
Alexandre Belloni added the core support for the backup mode on Atmel SAMA5D2, a suspend/resume state with significant power savings.
Boris Brezillon switched Atmel platforms to use the new binding for the EBI and NAND controllers.
Boris Brezillon added support for timing configuration in the Atmel NAND driver.
Quentin Schulz added suspend/resume support to the Bosch m_can driver, used on Atmel platforms.
Support for Marvell ARM platforms
Antoine Ténart contributed a completely new driver (3200+ lines of code) for the Inside Secure EIP197 cryptographic engine, used in the Marvell Armada 7K and 8K processors. He also subsequently contributed a number of fixes and improvements for this driver.
Antoine Ténart improved the existing mvmdio driver, used to communicate with Ethernet PHYs over MDIO on Marvell platforms to support the XSMI variant found on Marvell Armada 7K/8K, used to communicate with 10G capable PHYs.
Antoine Ténart contributed minimal support for 10G Ethernet in the mvpp2 driver, used on Marvell Armada 7K/8K. For now, the driver still relies on low-level initialization done by the bootloader, but additional changes in 4.14 and 4.15 will remove this limitation.
Grégory Clement added a new pinctrl driver to configure the pin-muxing on the Marvell Armada 37xx processors.
Grégory Clement did a large number of changes to the clock drivers used on the Marvell Armada 7K/8K processors to prepare the addition of pinctrl support.
Grégory Clement added support for Marvell Armada 7K/8K to the existing mvebu-gpio driver.
Thomas Petazzoni added support for the ICU, a specialized interrupt controller used on the Marvell Armada 7K/8K, for all devices located in the CP110 part of the processor.
Thomas Petazzoni removed a work-around to properly resume per-CPU interrupts on the older Marvell Armada 370/XP platforms.
Support for RaspberryPi platforms
Boris Brezillon added runtime PM support to the HDMI encoder driver used on RaspberryPi platforms, and contributed a few other fixes to the VC4 DRM driver.
Bootlin engineers are not only contributors, but also maintainers of various subsystems in the Linux kernel, which means they are involved in the process of reviewing, discussing and merging patches contributed to those subsystems:
Maxime Ripard, as the Allwinner platform co-maintainer, merged 113 patches from other contributors
Boris Brezillon, as the MTD/NAND maintainer, merged 62 patches from other contributors
Alexandre Belloni, as the RTC maintainer and Atmel platform co-maintainer, merged 57 patches from other contributors
Grégory Clement, as the Marvell EBU co-maintainer, merged 47 patches from other contributors
Here is the commit by commit detail of our contributors to 4.13:
The Kernel Recipes conference has become over the last few years a very interesting conference, with an original single track format and a limited number of attendees, which fosters communication and networking. Held in Paris, France, it is obviously a conference of choice for Bootlin engineers to attend and speak at. We participated to multiple editions, Bootlin engineer Maxime Ripard gave a talk at the 2014 edition, while Thomas Petazzoni gave a talk at the 2013 edition.
In 2017, the organizers decided to complement the 3-day Kernel Recipes conference with a 1-day Embedded Recipes event, and Bootlin will participate by having two engineers attend those events and give talks:
The Linux Plumbers conference has established itself as a major conference in the Linux ecosystem, discussing numerous aspects of the low-level layers of the Linux software stack. Linux Plumbers is organized around a number of micro-conferences, plus a number of more regular talks.
Bootlin already participated to several previous editions of Linux Plumbers, and will again participate to this year’s edition that takes place in Los Angeles on September 13-15. Bootlin engineers Boris Brezillon, Alexandre Belloni, Grégory Clement and Thomas Petazzoni will attend the conference.
If you’re attending this conference, or are located in the Los Angeles area, and want to meet us, do not hesitate to drop us a line at info@bootlin.com. You can also follow Bootlin Twitter feed for updates during the conference.
Two months ago, we announced a new service from Bootlin: free and ready-to-use Linux cross-compilation toolchains, for a large number of architectures and C libraries, available at https://toolchains.bootlin.com/.
Bleeding edge toolchain updates
All our bleeding edge toolchains have been updated, with the latest version of the toolchain components:
gcc 7.2.0, which was released 2 days ago
glibc 2.26, which was released 2 weeks ago
binutils 2.29
gdb 8.0
Those bleeding edge toolchains are now based on Buildroot 2017.08-rc2, which brings a nice improvement: the host tools (gcc, binutils, etc.) are no longer linked statically against gmp, mpfr and other host libraries. They are dynamically linked against them with an appropriate rpath encoded into the gcc and binutils binaries to find those shared libraries regardless of the installation location of the toolchain.
However, due to gdb 8.0 requiring a C++11 compiler on the host machine (at least gcc 4.8), our bleeding edge toolchains are now built in a Debian Jessie system instead of Debian Squeeze, which means that at least glibc 2.14 is needed on the host system to use them.
The only toolchains for which the tests are not successful are the MIPS64R6 toolchains, due to the Linux kernel not building properly for this architecture with gcc 7.x. This issue has already been reported upstream.
Stable toolchain updates
We haven’t changed the component versions of our stable toolchains, but we made a number of fixes to them:
The armv7m and m68k-coldfire toolchains have been rebuilt with a fixed version of elf2flt that makes the toolchain linker directly usable. This fixes building the Linux kernel using those toolchains.
The mips32r5 toolchain has been rebuilt with NaN 2008 encoding (instead of NaN legacy), which makes the resulting userspace binaries actually executable by the Linux kernel, which expects NaN 2008 encoding on mips32r5 by default.
Most mips toolchains for musl have been rebuilt, with Buildroot fixes for the creation of the dynamic linker symbolic link. This has no effect on the toolchain itself, but also the tests under Qemu to work properly and validate the toolchains.
Each architecture now has a page that lists all toolchain versions available. This allows to easily find a toolchain that matches your requirements (in terms of gcc version, kernel headers version, etc.). See All aarch64 toolchains for an example.
Linus Torvalds has released the 4.12 Linux kernel a week ago, in what is the second biggest kernel release ever by number of commits. As usual, LWN had a very nice coverage of the major new features and improvements: first part, second part and third part.
LWN has also published statistics about the Linux 4.12 development cycles, showing:
Bootlin as the #14 contributing company by number of commits, with 221 commits, between Broadcom (230 commits) and NXP (212 commits)
Bootlin as the #14 contributing company number of changed lines, with 16636 lines changed, just two lines less than Mellanox
Bootlin engineer and MTD NAND maintainer Boris Brezillon as the #17 most active contributor by number of lines changed.
Our most important contributions to this kernel release have been:
On Atmel AT91 and SAMA5 platforms:
Alexandre Belloni has continued to upstream the support for the SAMA5D2 backup mode, which is a very deep suspend to RAM state, offering very nice power savings. Alexandre touched the core code in arch/arm/mach-at91 as well as pinctrl and irqchip drivers
Boris Brezillon has converted the Atmel PWM driver to the atomic API of the PWM subsystem, implemented suspend/resume and did a number of fixes in the Atmel display controller driver, and also removed the no longer used AT91 Parallel ATA driver.
Quentin Schulz improved the suspend/resume hooks in the atmel-spi driver to support the SAMA5D2 backup mode.
On Allwinner platforms:
Mylène Josserand has made a number of improvements to the sun8i-codec audio driver that she contributed a few releases ago.
Maxime Ripard added devfreq support to dynamically change the frequency of the GPU on the Allwinner A33 SoC.
Quentin Schulz added battery charging and ADC support to the X-Powers AXP20x and AXP22x PMICs, found on Allwinner platforms.
Quentin Schulz added a new IIO driver to support the ADCs found on numerous Allwinner SoCs.
Quentin Schulz added support for the Allwinner A33 built-in thermal sensor, and used it to implement thermal throttling on this platform.
On Marvell platforms:
Antoine Ténart contributed Device Tree changes to describe the cryptographic engines found in the Marvell Armada 7K and 8K SoCs. For now only the Device Tree description has been merged, the driver itself will arrive in Linux 4.13.
Grégory Clement has contributed a pinctrl and GPIO driver for the Marvell Armada 3720 SoC (Cortex-A53 based)
Grégory Clement has improved the Device Tree description of the Marvell Armada 3720 and Marvell Armada 7K/8K SoCs and corresponding evaluation boards: SDHCI and RTC are now enabled on Armada 7K/8K, USB2, USB3 and RTC are now enabled on Armada 3720.
Thomas Petazzoni made a significant number of changes to the mvpp2 network driver, finally adding support for the PPv2.2 version of this Ethernet controller. This allowed to enable network support on the Marvell Armada 7K/8K SoCs.
Thomas Petazzoni contributed a number of fixes to the mv_xor_v2dmaengine driver, used for the XOR engines on the Marvell Armada 7K/8K SoCs.
Thomas Petazzoni cleaned-up the MSI support in the Marvell pci-mvebu and pcie-aardvark PCI host controller drivers, which allowed to remove a no-longer used MSI kernel API.
On the ST SPEAr600 platform:
Thomas Petazzoni added support for the ADC available on this platform, by adding its Device Tree description and fixing a clock driver bug
Thomas did a number of small improvements to the Device Tree description of the SoC and its evaluation board
Thomas cleaned up the fsmc_nand driver, which is used for the NAND controller driver on this platform, removing lots of unused code
In the MTD NAND subsystem:
Boris Brezillon implemented a mechanism to allow vendor-specific initialization and detection steps to be added, on a per-NAND chip basis. As part of this effort, he has split into multiple files the vendor-specific initialization sequences for Macronix, AMD/Spansion, Micron, Toshiba, Hynix and Samsung NANDs. This work will allow in the future to more easily exploit the vendor-specific features of different NAND chips.
Other contributions:
Maxime Ripard added a display panel driver for the ST7789V LCD controller
In addition, several Bootlin engineers are also maintainers of various kernel subsystems. During this release cycle, they reviewed and merged a number of patches from kernel contributors:
Maxime Ripard, as the Allwinner co-maintainer, merged 94 patches
Boris Brezillon, as the NAND maintainer and MTD co-maintainer, merged 64 patches
Alexandre Belloni, as the RTC maintainer and Atmel co-maintainer, merged 38 patches
Grégory Clement, as the Marvell EBU co-maintainer, merged 32 patches
The details of all our contributions for this release:
For all embedded Linux developers, cross-compilation toolchains are part of the basic tool set, as they allow to build code for a specific CPU architecture and debug it. Until a few years ago, CodeSourcery was providing a lot of high quality pre-compiled toolchains for a wide range of architectures, but has progressively stopped doing so. Linaro provides some freely available toolchains, but only targetting ARM and AArch64. kernel.org has a set of pre-built toolchains for a wider range of architectures, but they are bare metal toolchains (cannot build Linux userspace programs) and updated infrequently.
To fill in this gap, Bootlin is happy to announce its new service to the embedded Linux community: toolchains.bootlin.com.
This web site provides a large number of cross-compilation toolchains, available for a wide range of architectures, in multiple variants. The toolchains are based on the classical combination of gcc, binutils and gdb, plus a C library. We currently provide a total of 138 toolchains, covering many combinations of:
Architectures: AArch64 (little and big endian), ARC, ARM (little and big endian, ARMv5, ARMv6, ARMv7), Blackfin, m68k (Coldfire and 68k), Microblaze (little and big endian), MIPS32 and MIPS64 (little and big endian, with various instruction set variants), NIOS2, OpenRISC, PowerPC and PowerPC64, SuperH, Sparc and Sparc64, x86 and x86-64, Xtensa
Versions: for each combination, we provide a stable version which uses slightly older but more proven versions of gcc, binutils and gdb, and we provide a bleeding edge version with the latest version of gcc, binutils and gdb.
After being generated, most of the toolchains are tested by building a Linux kernel and a Linux userspace, and booting it under Qemu, which allows to verify that the toolchain is minimally working. We plan on adding more tests to validate the toolchains, and welcome your feedback on this topic. Of course, not all toolchains are tested this way, because some CPU architectures are not emulated by Qemu.
The toolchains are built with Buildroot, but can be used for any purpose: build a Linux kernel or bootloader, as a pre-built toolchain for your favorite embedded Linux build system, etc. The toolchains are available in tarballs, together with licensing information and instructions on how to rebuild the toolchain if needed.
We are very much interested in your feedback about those toolchains, so do not hesitate to report bugs or make suggestions in our issue tracker!
This work was done as part of the internship of Florent Jacquet at Bootlin.
Over the last few releases, a significant number of improvements in terms of QA-related tooling has been done in the Buildroot project. As an embedded Linux build system, Buildroot has a growing number of packages, and maintaining all of those packages is a challenge. Therefore, improving the infrastructure around Buildroot to make sure that packages are in good shape is very important. Below we provide a summary of the different improvements that have been made.
check-package script
Very much like the Linux kernel has a checkpatch.pl script to help contributors validate their patches, Buildroot now has a check-package script that allows to validate the coding style and check for common errors in Buildroot packages. Contributors are encouraged to use it to avoid common mistakes typically spotted during the review process.
check-package is capable of checking the .mk file, the Config.in, the .hash file of packages as well as the patches that apply to packages.
Contributed by Ricardo Martincoski, and written in Python, this tool will first appear in the next stable release 2017.05, to be published at the end of the month.
Buildroot’s page of package stats has been updated with a new column Warnings that lists the number of check-package issues to be fixed on each package. Not all packages have been fixed yet!
test-pkg script
Besides coding style issues, another problem that the Buildroot community faces when accepting contributions of new packages or package updates, is that those contributions have rarely been tested on a large number of toolchain/architecture configurations. To help contributors in this testing, a test-pkg tool has been added.
Provided a Buildroot configuration snippet that enables the package to be tested, test-pkg tool will iterate over a number of toolchain/architecture configurations and make sure the package builds fine for all those configurations. The set of configurations being tested is the one used by Buildroot autobuilder’s infrastructure, which allows us to make sure that a package will not fail to build as soon as it is added into the tree. Contributors are therefore encouraged to use this tool for their package related contributions.
A very primitive version of this tool was originally contributed by Thomas Petazzoni, but it’s finally Yann E. Morin who took over, cleaned up the code, extended it and made it more generic, and contributed the final tool.
Runtime testing infrastructure
The Buildroot autobuilder infrastructure has been running for several years, and tests random configurations of Buildroot packages to make sure they build properly. This infrastructure allows the Buildroot developers to make sure that all combinations of packages build properly on all architectures, and has been a very useful tool to help increase Buildroot quality. However, this infrastructure does not perform any sort of runtime testing.
To address this, a new runtime testing infrastructure has recently been contributed to Buildroot by Thomas Petazzoni. Contrary to the autobuilder infrastructure that tests random configurations, this runtime testing infrastructure tests a well-defined set of configurations, and uses Qemu to make sure that they work properly. Located in support/testing this test infrastructure currently has only 25 test cases, but we plan to extend this over time with more and more tests.
For example, the ISO9660 test makes sure that Buildroot is capable of building an ISO9660 image that boots properly under Qemu. The test suite validates that it works in different configurations: using either Grub, Grub2 or Syslinux as a bootloader, and using a root filesystem entirely contained in an initramfs or inside the ISO9660 filesystem itself.
Besides doing run-time tests of packages, this infrastructure will also allow us to test various core Buildroot functionalities. We also plan to have the tests executed on a regular basis on a CI infrastructure such as Gitlab CI.
DEVELOPERS file and e-mail notification
Back in the 2016.11 release, we added a top-level file called DEVELOPERS, which plays more or less the same role as the Linux kernel’s MAINTAINERS file: associate parts of Buildroot, especially packages, with developers interested in this area. Since Buildroot doesn’t have a concept of per-package maintainers, we decided to simply call the file DEVELOPERS.
Thanks to the DEVELOPERS file, we are able to:
Provide the get-developers tool, which parses patches and returns a list of e-mail addresses to which the patches should be sent, very much like the Linux kernel get_maintainer.pl tool. This allows developers who have contributed a package to be notified when a patch is proposed for the same package, and get the chance to review/test the patch.
Notify the developers of a package of build failures caused by this package in the Buildroot autobuilder infrastructure. So far, all build results of this infrastructure were simply sent every day on the mailing list, which made it unpractical for individual developers to notice which build failures they should look at. Thanks to the DEVELOPERS file, we now send a daily e-mail individually to the developers whose packages are affected by build failures.
Notify the developers of the support for a given CPU architecture of build failures caused on the autobuilders for this architecture, in a manner similar to what is done for packages.
Thanks to this, we have seen developers who were not regularly following the Buildroot mailing list contribute again fixes for build failures caused by their packages, increasing the overall Buildroot quality. The DEVELOPERS file and the get-developers script, as well as the related improvements to the autobuilder infrastructure were contributed by Thomas Petazzoni.
Build testing of defconfigs on Gitlab CI
Buildroot contains a number of example configurations called defconfigs for various hardware platforms, which allow to build a minimal embedded Linux system, known to work on such platforms. At the time of this writing, Buildroot has 146 defconfigs for platforms ranging from popular development boards (Raspberry Pi, BeagleBone, etc.) to evaluation boards from SoC vendors and Qemu machine emulation.
In order to make sure all those defconfigs build properly, we used to have a job running on Travis CI, but we started to face limitations, especially in the maximum allowed build duration. Therefore, Arnout Vandecappelle migrated this on Gitlab CI and things have been running smoothly since then.
With 137 patches contributed, Bootlin is the 18th contributing company according to the Kernel Patch Statistics. Bootlin engineer Maxime Ripard appears in the list of top contributors by changed lines in the LWN statistics.
Our most important contributions to this release have been:
Support for Atmel platforms
Alexandre Belloni improved suspend/resume support for the Atmel watchdog driver, I2C controller driver and UART controller driver. This is part of a larger effort to upstream support for the backup mode of the Atmel SAMA5D2 SoC.
Alexandre Belloni also improved the at91-poweroff driver to properly shutdown LPDDR memories.
Boris Brezillon contributed a fix for the Atmel HLCDC display controller driver, as well as fixes for the atmel-ebi driver.
Support for Allwinner platforms
Boris Brezillon contributed a number of improvements to the sunxi-nand driver.
Mylène Josserand contributed a new driver for the digital audio codec on the Allwinner sun8i SoC, as well a the corresponding Device Tree changes and related fixes. Thanks to this driver, Mylène enabled audio support on the R16 Parrot and A33 Sinlinx boards.
Maxime Ripard contributed numerous improvements to the sunxi-mmc MMC controller driver, to support higher data rates, especially for the Allwinner A64.
Maxime Ripard contributed official Device Tree bindings for the ARM Mali GPU, which allows the GPU to be described in the Device Tree of the upstream kernel, even if the ARM kernel driver for the Mali will never be merged upstream.
Maxime Ripard contributed a number of fixes for the rtc-sun6i driver.
Maxime Ripard enabled display support on the A33 Sinlinx board, by contributing a panel driver and the necessary Device Tree changes.
Maxime Ripard continued his clean-up effort, by converting the GR8 and sun5i clock drivers to the sunxi-ng clock infrastructure, and converting the sun5i pinctrl driver to the new model.
Quentin Schulz added a power supply driver for the AXP20X and AXP22X PMICs used on numerous Allwinner platforms, as well as numerous Device Tree changes to enable it on the R16 Parrot and A33 Sinlinx boards.
Support for Marvell platforms
Grégory Clement added support for the RTC found in the Marvell Armada 7K and 8K SoCs.
Grégory Clement added support for the Marvell 88E6141 and 88E6341 Ethernet switches, which are used in the Armada 3700 based EspressoBin development board.
Romain Perier enabled the I2C controller, SPI controller and Ethernet switch on the EspressoBin, by contributing Device Tree changes.
Thomas Petazzoni contributed a number of fixes to the OMAP hwrng driver, which turns out to also be used on the Marvell 7K/8K platforms for their HW random number generator.
Thomas Petazzoni contributed a number of patches for the mvpp2 Ethernet controller driver, preparing the future addition of PPv2.2 support to the driver. The mvpp2 driver currently only supports PPv2.1, the Ethernet controller used on the Marvell Armada 375, and we are working on extending it to support PPv2.2, the Ethernet controller used on the Marvell Armada 7K/8K. PPv2.2 support is scheduled to be merged in 4.12.
Support for RaspberryPi platforms
Boris Brezillon contributed Device Tree changes to enable the VEC (Video Encoder) on all bcm283x platforms. Boris had previously contributed the driver for the VEC.
In addition to our direct contributions, a number of Bootlin engineers are also maintainers of various subsystems in the Linux kernel. As part of this maintenance role:
Maxime Ripard, co-maintainer of the Allwinner ARM platform, reviewed and merged 85 patches from contributors
Alexandre Belloni, maintainer of the RTC subsystem and co-maintainer of the Atmel ARM platform, reviewed and merged 60 patches from contributors
Grégory Clement, co-maintainer of the Marvell ARM platform, reviewed and merged 42 patches from contributors
Boris Brezillon, maintainer of the MTD NAND subsystem, reviewed and merged 8 patches from contributors
Here is the detailed list of contributions, commit per commit:
Last month, five engineers from Bootlin participated to the Embedded Linux Conference in Portlan, Oregon. It was once again a great conference to learn new things about embedded Linux and the Linux kernel, and to meet developers from the open-source community.
Bootlin team at work at ELC 2017, with Maxime Ripard, Antoine Ténart, Mylène Josserand and Quentin Schulz
Of course, the slides from many other talks are progressively being uploaded, and the Linux Foundation published the video recordings in a record time: they are all already available on Youtube!
Below, each Bootlin engineer who attended the conference has selected one talk he/she has liked, and gives a quick summary of the talk, hopefully to encourage you watch the corresponding video recording.
Using SWupdate to Upgrade your system, Gabriel Huau
Gabriel Huau from Witekio did a great talk at ELC about SWUpdate, a tool created by Denx to update your system. The talk gives an overview of this tool, how it is working and how to use it. Updating your system is very important for embedded devices to fix some bugs/security fixes or add new features, but in an industrial context, it is sometimes difficult to perform an update: devices not easily accessible, large number of devices and variants, etc. A tool that can update the system automatically or even Over The Air (OTA) can be very useful. SWUpdate is one of them.
SWUpdate allows to update different parts of an embedded system such as the bootloader, the kernel, the device tree, the root file system and also the application data.
It handles different image types: UBI, MTD, Raw, Custom LUA, u-boot environment and even your custom one. It includes a notifier to be able to receive feedback about the updating process which can be useful in some cases. SWUPdate uses different local and OTA/remote interfaces such as USB, SD card, HTTP, etc. It is based on a simple update image format to indicate which images must be updated.
Many customizations can be done with this tool as it is provided with the classic menuconfig configuration tool. One great thing is that this tool is supported by Yocto Project and Buildroot so it can be easily tested.
Do not hesitate to have a look to his slides, the video of his talk or directly test SWUpdate!
GCC/Clang Optimizations for embedded Linux, Khem Raj
Khem Raj from Comcast is a frequent speaker at the Embedded Linux Conference, and one of his strong fields of expertise is C compilers, especially LLVM/Clang and Gcc. His talk at this conference can interest anyone developing code in the C language, to know about optimizations that the compilers can use to improve the performance or size of generated binaries. See the video and slides.
One noteworthy optimization is Clang’s -Oz (Gcc doesn’t have it), which goes even beyond -Os, by disabling loop vectorization. Note that Clang already performs better than Gcc in terms of code size (according to our own measurements). On the topic of bundle optimizations such as -O2 or -Os, Khem added that specific optimizations can be disabled in both compilers through the -fno- command line option preceding the name of a given optimization. The name of each optimization in a given bundle can be found through the -fverbose-asm command line option.
Another new optimization option is -Og, which is different from the traditional -g option. It still allows to produce code that can be debugged, but in a way that provides a reasonable level of runtime performance.
On the performance side, he also recalled the Feedback-Directed Optimizations (FDO), already covered in earlier Embedded Linux Conferences, which can be used to feed the compiler with profiler statistics about code branches. The compiler can use such information to optimize branches which are the more frequent at run-time.
Khem’s last advise was not to optimize too early, and first make sure you do your debugging and profiling work first, as heavily optimized code can be very difficult to debug. Therefore, optimizations are for well-proven code only.
Note that Khem also gave a similar talk in the IoT track for the conference, which was more focused on bare-metal code optimization code and portability: “Optimizing C for microcontrollers” (slides, video).
A Journey through Upstream Atomic KMS to Achieve DP Compliance, Manasi Navare
This talk was about the journey of a new comer in the mainline kernel community to fix the DisplayPort support in Intel i915 DRM driver. It first presented what happens from the moment we plug a cable in a monitor until we actually see an image, then where the driver is in the kernel: in the DRM subsystem, between the hardware (an Intel Integrated Graphics device) and the libdrm userspace library on which userspace applications such as the X server rely.
The bug to fix was that case when the driver would fail after updating to the requested resolution for a DP link. The other existing drivers usually fail before updating the resolution, so Manasi had to add a way to tell the userspace the DP link failed after updating the resolution. Such addition would be useless without applications using this new information, therefore she had to work with their developers to make the applications behave correctly when reading this important information.
With a working set of patches, she thought she had done most of the work with only the upstreaming left and didn’t know it would take her many versions to make it upstream. She wished to have sent a first version of a driver for review earlier to save time over the whole development plus upstreaming process. She also had to make sure the changes in the userspace applications will be ready when the driver will be upstreamed.
The talk was a good introduction on how DisplayPort works and an excellent example on why involving the community even in early stages of the development process may be a good idea to quicken the overall driver development process by avoiding complete rewriting of some code parts when upstreaming is under way.
Stephen did a great talk about one thing that is often overlooked, and really shouldn’t: Timekeeping. He started by explaining the various timekeeping mechanisms, both in hardware and how Linux use them. That meant covering the counters, timers, the tick, the jiffies, and the various POSIX clocks, and detailing the various frameworks using them. He also explained the various bugs that might be encountered when having a too naive counter implementation for example, or using the wrong POSIX clock from an application.
Karim did a very good introduction to Android Things. His talk was a great overview of what this new OS from Google targeting embedded devices is, and where it comes from. He started by showing the history of Android, and he explained what this system brought to the embedded market. He then switched to the birth of Android Things; a reboot of Google’s strategy for connected devices. He finally gave an in depth explanation of the internals of this new OS, by comparing Android Things and Android, with lots of examples and demos.
Android Things replaces Brillo / Weave, and unlike its predecessor is built reusing available tools and services. It’s in fact a lightweight version of Android, with many services removed and a few additions like the PIO API to drive GPIO, I2C, PWM or UART controllers. A few services were replaced as well, most notably the launcher. The result is a not so big, but not so small, system that can run on headless devices to control various sensors; with an Android API for application developers.
Linux 4.13 was 
