DMAEngine Documentation: Work (finally) in Progress

While developping a DMA controller driver for the Allwinner A31 SoCs (that eventually got merged in the 3.17 kernel), I’ve realised how under-documented the DMAEngine kernel subsystem was, especially for a newcomer like I was.

After discussing this with a few other kernel developers in the same situation, I finally started to work on such a documentation during the summer, and ended up submitting it at the end of July. As you might expect, it triggered a lot of questions, comments and discussions that enhanced a lot the documentation itself but also pointed out some inconsistencies in the API, obscure areas or just enhancements.

This also triggered an effort to clean up these areas, and hopefully, a lot more will follow, allowing to eventually clean up the framework as a whole.

And the good thing is that this documentation has been merged by the DMAEngine maintainer and is visible in linux-next, feel free to read it, and enhance it!

Yocto Project and OpenEmbedded training materials published

Yocto Project and OpenEmbedded trainingAs we announced in out latest newsletter, we recently launched a new Yocto Project and OpenEmbedded development training course.

The first public session will take place in Toulouse, France on November 18-20 and we still have a few seats available. We can also deliver on-site sessions at the location of your choice, see our Training cost and registration page for more details.

However, what brings us here today is that we are happy to announce the release of all the training materials of this new course: like all Bootlin training materials, they are available under the Creative Commons Attribution Share-Alike license.

Fully committed to its knowledge sharing principles, Bootlin has chosen to publish those materials even before the first session has taken place.

The materials available are:

We of course welcome reviews, feedback and comments about these materials, in order to improve them where needed. Send us your comments!

Bootlin registered as Yocto Project Participant.

Yocto_Project_Badge_Participant_Web_RGB
Earlier this month, Bootlin applied and was elected Yocto Project Participant by the Yocto Project Advisory Board. This badge is awarded to people and companies actively participating to the Yocto Project and promoting it.

We have mainly contributed to the meta-fsl-arm and meta-fsl-arm-extra layers but we also have some contributions in OpenEmbedded Core and in the meta-ti layer.

Bootlin offers a Yocto Project and OpenEmbedded training course that we can deliver at your location, or that you can attend by joining one of our public sessions. Our engineers are also available to provide consulting and development services around the Yocto Project, to help you use this tool for your embedded Linux projects. Do not hesitate to contact us!

Linux 3.17 released, Bootlin 14th contributing company

PenguinLinux 3.17 has been released a few days ago. One can read the coverage of the 3.17 merge window by LWN (part 1 and part 2) to get some details about the new features brought by this kernel release.

As usual, Bootlin has continued to contribute a significant number of patches to this kernel release, even though with 147 patches, our contribution has been less important than for the 3.16 release for which we contributed 388 patches. With 147 patches merged, Bootlin is the 14th contributing company by the number of patches, according to the statistics.

Our contributions remain mainly focused on support for various families of ARM processors:

  • For the Atmel processors
    • Switched to use the generic PWM framework instead of custom PWM drivers. This allowed to remove three obsolete drivers (a backlight driver, a LED driver and a misc driver). This work was done by Alexandre Belloni.
    • Continue the migration to the common clock framework, by adding clock information to a large number of Atmel boards. Done by Alexandre Belloni.
    • Migration of the interrupt controller driver from arch/arm/mach-at91 to drivers/irqchip. Done by Boris Brezillon.
  • For the Marvell EBU processors (Armada 370, 375, 38x, XP)
    • Addition of the mvpp2 network driver, which is used on the Armada 375 SoC. This work was done by Marcin Wojtas from Semihalf, with a lot of review, help and debugging done by Ezequiel Garcia.
    • Addition of cpuidle support for Armada 370 and Armada 38x. This work was done by Grégory Clement and Thomas Petazzoni.
    • Preparation work to enable cpufreq on Armada XP was merged. However the feature cannot be enabled yet due to missing features in the cpufreq-cpu0 driver. Done by Thomas Petazzoni.
  • For Marvell Berlin processors
    • SMP support has been added. Done by Antoine Ténart.
    • Description of the I2C controller has been added to the Device Tree. Done by Antoine Ténart.
    • Support for AHCI has been added. Also done by Antoine Ténart.
  • For Allwinner processors
    • New DMA controller driver for the DMA engine of the Allwinner A31 SoC. Done by Maxime Ripard.
    • A number of fixes and improvements to the pin-muxing driver for Allwinner platforms. Done by Maxime Ripard.
    • Support for the Merrii A31 Hummingbird board has been added. Done by Maxime Ripard.
  • Other changes
    • Addition of a helper function to convert an ONFI timing mode into the according NAND timings. Done by Boris Brezillon.
    • Addition of a driver for the Foxlink FL500WVR00-A0T panel. Done by Boris Brezillon.

The detailed list of our contributions:

Atmel SAMA5D4 support in the mainline Linux kernel

Atmel SAMA5D4Atmel announced its new ARM Cortex-A5-based SoC on October 1, the SAMA5D4. Compared to the previous Cortex-A5 SoC from Atmel, the SAMA5D3, this new version brings a L2 cache, NEON, a slightly different clock tree, a hardware video decoder, and Trustzone support.

Bootlin engineers have worked since several months with Atmel engineers to prepare and submit the support for this new SoC to the mainline Linux kernel. We have actually submitted the patches on September, 11th, almost a month before the official release of the new chip! This means that most of the support for this new SoC will already be part of the upcoming 3.18 kernel release. Meanwhile, it is already possible to test it out by using the linux-next repository.

There are however a few pieces missing pieces to support all aspects of the chip:

  • A few patches are needed to get proper NAND flash controller support.
  • The DMA controller is brand new in this SAMA5D4 SoC, and the DMA controller driver has not yet been merged, even though the patches have been posted a long time ago, and are currently in their sixth iteration.
  • Display support, through a DRM/KMS driver, is also being reviewed. The driver, written by Bootlin engineer Boris Brezillon, was initially designed for the sam9x5 and sam5d3, but will be compatible with sama5d4 as well. The patch series is currently in its seventh iteration.

The last big missing part is support for non-secure mode: for the moment, the system always runs in secure mode. Running the kernel in non-secure mode will require some more work but an initial version will probably be pushed during the next development cycle.

Besides this work on SAMA5D4 support ahead of its public release, Bootlin is also doing a lot of maintenance work on all the Atmel ARM platforms in the Linux kernel: migration to the Device Tree, to the clock framework, to several other new subsystems, etc. See the summary of our kernel contributions to 3.16, 3.15 and 3.14.

Through this work, the Bootlin engineering team has a very deep knowledge of the Linux support for Atmel ARM processors. Do not hesitate to contact us if you need help to bring up the bootloader or kernel on your custom Atmel ARM platform! It is also worth mentioning that Free-Electrons is part of the Atmel partner ecosystem.

2014 Q3 newsletter

Bootlin is happy to share some news about the latest training and contribution activities of the company.

Kernel contributions

Since our last newsletter, our engineering team continued to make significant contributions to the Linux kernel, especially in the area of supporting ARM processors and platforms:

  • 218 patches from Bootlin were merged into Linux 3.15, making Bootlin the 12th contributing company for this release by number of patches. See our blog post.
  • 388 patches from Bootlin were merged into Linux 3.16, making Bootlin the 7th contributing company for this release, by number of patches. See our blog post.
  • For the upcoming 3.17 release, we already have 146 patches merged, and we have a lot more work being done for future kernel releases.

The major areas of our contributions were:

  • The addition of an ubiblk driver, which allows traditional block filesystems to be used on top of UBI devices, and therefore on NAND flash storage. Only read-only support is available, but it already allows to make use of the super efficient SquashFS filesystem on top of NAND flash in a safe way.
  • Another major addition is support for the new Marvell Armada 375 and Armada 38x processors. In just two releases (3.15 and 3.16) we almost pushed entire support for these new processors. The network driver for Armada 375 is one missing piece, coming in 3.17.
  • Our maintenance work on the Atmel AT91 and SAMA5 processors has continued, with more conversion to the Device Tree, the common clock framework, and other modern kernel mechanisms. We have also developed the DRM/KMS (graphics) driver for the SAMA5D3 SoC, which has already been posted and should hopefully be merged soon.
  • Our work to support the Marvell Berlin processor has started to be merged in 3.16. This processor is used in various TVs, set-top boxes or devices like the Google Chromecast. Basic support was merged including Device Trees, clock drivers, pin-muxing driver, GPIO and SDHCI support. AHCI support will be in 3.17, and USB and network support should be in 3.18.
  • Additional work was done on support for Allwinner ARM SoCs, especially the A31 processor: SPI and I2C support, drivers for the P2WI bus and the PRCM controller, and support for USB.

We now have broad experience in writing kernel drivers and getting code merged into the mainline tree. Do not hesitate to contact us if you need help to develop Linux kernel drivers, or to support a new board or processor.

Buildroot contributions

Our involvement into the Buildroot project, a popular embedded Linux build system, is going on. We have merged 159 patches in the 2014.05 release of the project (total of 1293 patches), and 129 patches in the 2014.08 release of the project (total of 1353 patches). Moreover, our engineer Thomas Petazzoni is regularly an interim maintainer of the project, when the official maintainer Peter Korsgaard is not available. Some of the major features we contributed: major improvements to Python 3 support, addition of EFI bootloaders, addition of support for the Musl C library.

Regular embedded Linux projects

Of course, we also conducted embedded Linux development and boot time optimization projects for various embedded system makers, with less visible impact on community projects. However, we will try to share generic technical experience from such projects through future blog posts.

New training course: Yocto Project and OpenEmbedded

A large number of embedded Linux projects use embedded Linux build systems to integrate the various software components of the system into a working root filesystem image. Among the solutions available to achieve this, the Yocto Project and OpenEmbedded are very popular.

We have therefore launched a new 3 day Yocto Project and OpenEmbedded training course to help engineers and companies who are using, or are interested in using these solutions for their embedded Linux projects. Starting from the basics of understanding the core principles of Yocto, the training course goes into the details of writing package recipes, integrating support for a board into Yocto, creating custom images, and more.

The detailed agenda of the training course is available. You can order this training course at your location, or participate to the first public session organized on November 18-20 in France.

Embedded Linux training course updated

The embedded Linux ecosystem is evolving very quickly, and therefore we are continuously updating our training courses to match the latest developments. As part of this effort, we have recently conducted a major update to our Embedded Linux course: the hardware platform used for the practical labs has been changed to the popular and very interesting Atmel Xplained SAMA5D3, and many practical labs have been improved to provide a more useful learning experience. See our blog post for more details.

Mailing list for training participants

We have launched a new service for the participants to our training sessions: a mailing list dedicated to them, and through which they can ask additional questions after the course, share their experience, get in touch with other training participants and Bootlin engineers. Of course, all Bootlin engineers are on the mailing list and participate to the discussions. Another useful service offered by our training courses!

This resource is no longer available, but participants to our training sessions are still welcome to contact us by e-mail.

Conferences: ELC, ELCE, Kernel Recipes

The Bootlin engineering team will participate to the Embedded Linux Conference Europe and Linux Plumbers, next month in Düsseldorf, Germany. Several Bootlin engineers will also be giving talks during ELCE:

In addition, Thomas will participate to the Buildroot Developers Day, taking place right before the Embedded Linux Conference Europe in Düsseldorf.

See also our blog post about ELCE for more details.

Maxime Ripard and Michael Opdenacker will participate to the Kernel Recipes 2014 conference, on September 25-26 in Paris. Maxime will be giving his Allwinner kernel talk at this conference. See our blog post for more details.

Last but not least, we have recently published the videos of a number of talks from the previous Embedded Linux Conference, held earlier this year in San Jose. A lot of interesting material about embedded Linux! Check out our blog post for more details.

Upcoming training sessions

We have a number of public training sessions dates, with seats available:

Sessions and dates

Linux 3.16 released, Bootlin 7th contributing company

Linus Torvalds has released the 3.16 kernel a few weeks ago. Unfortunately, the KernelNewbies LinuxChanges page has not been updated, but LWN.net summaries of the merge window (part 1, part 2 and final part) give a good summary of the important changes available in Linux 3.16.

On Bootlin’sside, 3.16 has been our most active kernel cycle ever: we have merged 388 patches in this cycle, making Bootlin the 7th company contributing to the Linux kernel by number of patches according to the statistics. Bootlin is ranked right after Texas Instruments, and before Novell, Renesas or Google. (Note that the statistics rank Bootlin as 9th, but this includes the “Unknown” and “Hobbyists” categories which are not companies). This strong participation clearly shows Bootlin’sability to get code merged in the mainline Linux kernel, as we’ve progressively done since kernel 3.6 over the last two years.

We are therefore available to help companies willing to add support for their hardware (processor, system-on-chip, module, or board) to the mainline Linux kernel. Do not hesitate to contact to get the discussion started.

Our major contributions have again been focused on the support of various ARM processor families:

  • On the Atmel SoC family
    • Conversion of the SAM9RL processor to the Device Tree. Done by Alexandre Belloni.
    • Huge cleanup of ADC/touchscreen handling: improvements in the IIO at91_adc driver to support more SoC families, and conversions of several Atmel platforms to use this driver, and then finally removal of the old atmel_tsadcc driver. Done by Alexandre Belloni.
    • Numerous fixes to the clock handling on various SoCs, following their conversion to the Common Clock Framework. Done by Alexandre Belloni.
    • Conversion of the SAM9RL, SAM9x5 and SAM9n12 SoCs to the Common Clock Framework. Done by Boris Brezillon.
    • Boris Brezillon is now one of the official maintainers for AT91 clock support.
  • On the Allwinner SoC family
    • Addition of PWM support to sun4i and sun7i. Done by Alexandre Belloni.
    • Addition of SMBus support to the regmap subsystem. This was needed to support the P2WI bus of Allwinner A31. Done by Boris Brezillon.
    • New I2C driver for the P2WI bus of Allwinner A31, used to communicate with the PMIC. Done by Boris Brezillon.
    • Improvements to the Allwinner pinctrl driver needed to support the P2WI bus. Done by Boris Brezillon.
    • Addition of a driver for the PRCM (Power, Reset and Clock Management) unit of the Allwinner A31. Done by Boris Brezillon.
    • Numerous cleanups of the pinctrl driver for Allwinner. Done by Maxime Ripard.
    • Addition of the ARM PMU description in the Device Tree of Allwinner platforms. Done by Maxime Ripard.
    • Add USB support for Allwinner A31. Done by Maxime Ripard, with some help from Boris Brezillon.
    • Various improvements to Allwinner clock drivers. Done by Maxime Ripard.
  • On the Marvell Berlin SoC family
    • Addition of basic Device Tree descriptions for several Marvell Berlin processors and boards. Done by Antoine Ténart.
    • Addition of clock drivers and DT clock descriptions of the Marvell Berlin processors. Done by Alexandre Belloni.
    • Addition of the pinctrl drivers for the Marvell Berlin processors. Done by Antoine Ténart.
    • Enabling of SDHCI and GPIO support on Marvell Berlin. Done by Antoine Ténart.
  • On the Marvell EBU SoC family
    • Addition of watchdog support for Armada 375 and Armada 38x, which required some changes to the existing watchdog driver. Done by Ezequiel Garcia.
    • Addition of thermal support for Armada 375 and Armada 38x, which required some changes in the existing armada_thermal driver. Done by Ezequiel Garcia.
    • Improvements of the pxa3xx_nand driver used for NAND support on Armada 370/375/38x/XP to use the newly introduced ECC strength and step size Device Tree bindings, which allows from the Device Tree to override the ECC constraints described by ONFI, when needed to match the bootloader constraints. Done by Ezequiel Garcia.
    • Addition of a generic software TSO (TCP Segmentation Offload) layer, and the corresponding changes to enable this feature in the mv643xx_eth and mvneta network drivers. This gives a huge performance boost in transmit operations! Done by Ezequiel Garcia.
    • SMP support for Armada 375 and Armada 38x has been added. Done by Grégory Clement.
    • cpuidle support for Armada XP has been added. Done by Grégory Clement.
    • USB support (USB2 and USB3) for Armada 375 and Armada 38x has been added. Done by Grégory Clement.
    • Hardware I/O coherency support for Armada 375 and Armada 38x. Done by Thomas Petazzoni.
    • Enabling of the SDHCI and AHCI interfaces on Armada 38x. Done by Thomas Petazzoni.
    • Major clean-up of Marvell Orion5x support. This is an older ARMv5 family of processors from Marvell, having a lot of similarities with Kirkwood and more recent Armada. This cleanup include many Device Tree conversions, up to the point where a few Marvell Orion5x platforms can now be fully described using a Device Tree, with no board file. Done by Thomas Petazzoni.
    • Addition of a new Device Tree binding for fixed network links, i.e links that do not use a MDIO-controlled PHY. This involved both some generic PHY layer improvements, and corresponding changes in the Marvell-specific mvneta network driver. Done by Thomas Petazzoni.
    • Addition of a work-around for a relatively complex PCIe/L2 errata affecting Armada 375/38x, which fixes heavy PCIe traffic when the system is running with hardware I/O coherency enabled. Done by Thomas Petazzoni.

Here is the complete list of patches from Bootlin merged into the 3.16 kernel:

Linux 3.15 released, an overview of Bootlin contributions

The 3.15 of the Linux kernel was released just a few days ago by Linus Torvalds. As explained by LWN.net, the headline features in 3.15 include some significant memory management improvements, the renameat2() system call, file-private POSIX locks, a new device mapper target called dm-era, faster resume from suspend, and more. One can also read the coverage by LWN.net of the first part and the second part of the merge window to get more details about the major new features in this release.

As usual, Bootlin contributed to the Linux kernel during this 3.15 cycle, and with a total of 218 patches contributed, it’s a new record for Bootlin. According to the KPS statistics, Bootlin ranked #12 in the list of companies contributing to the Linux kernel for the 3.15 kernel (if you exclude the “Unknown” and “Hobbyists” categories, which aren’t really companies).

The main features contributed by Bootlin again centered around the support for ARM processors:

  • By far, the largest contribution this cycle was the initial support for the new Armada 375 and Armada 38x processors from Marvell. Gregory Clement, Ezequiel Garcia and Thomas Petazzoni have been working on the code to support these processors since a few months ago, and started pushing the patches to the public in February this year. For the Marvell Armada 38x processor, it means that the code was pushed in mainline even before the processor was announced publicly! The features supported in 3.15 for these processors are: interrupts, GPIO, clocks, pin-muxing, serial, I2C, SPI, timer, L2 cache, SDIO (only for 375), SATA (only 375), XOR, PCIe, MBus, networking (only for 38x), NOR and NAND support. Many other features such as SMP, I/O coherency and various other peripherals will be supported in 3.16.
  • Convert support for the Atmel AT91SAM9RL processor to the Device Tree, done by Alexandre Belloni.
  • Addition of iio-hwmon to the Freescale i.MX23 and i.MX28 processors, which allows to use the internal temperature sensor of the processor. Done by Alexandre Belloni.
  • Multiple fixes and improvements to the AT91 ADC support. Done by Alexandre Belloni.
  • Support for the watchdog in Armada 370 and Armada XP was added, done by Ezequiel Garcia.
  • A driver for the SPI controller found in Allwinner A31 SoC was added, as well as all the Device Tree information to describe this controller and related clocks. Done by Maxime Ripard.
  • Support for the I2C controller found in the Allwinner A31 SoC was added into the existing mv64xxx-i2c driver, as well as the necessary Device Tree information to use I2C on this SoC. Done by Maxime Ripard.
  • Audio support was enabled on the Armada 370 SoC, re-using existing code for Kirkwood, and therefore making audio work on the Armada 370 DB platform. Done by Thomas Petazzoni.
  • A number of issues in the PCIe support for Marvell processors have been fixed, thanks to the reports from a number of users. Done by Thomas Petazzoni, with help from these users.

We also contributed other things than just support for ARM processors:

  • The main contribution in this area is the addition of UBI block, a driver that allows to use read-only block filesystems such as squashfs on top of a UBI volume. The code was originally written by David Wagner who was an intern at Bootlin, and later taken by Ezequiel Garcia who did a lot of additional cleanup work and community discussion to get the driver merged. Some details about this feature can be found in the Linux-MTD documentation.
  • A generic Device Tree binding to express NAND ECC related information in the Device Tree was contributed by Ezequiel Garcia.
  • The quest to remove IRQF_DISABLED continued, by Michael Opdenacker.

In details, all our contributions are:

Marvell publishes the datasheet of the Armada 370 processor

thumb-armada-xpOver the last two years, Bootlin has contributed support for the Marvell Armada 370 and Marvell Armada XP processors to the mainline Linux kernel. These ARM processors are used mainly in Network Attached Storage devices but also in other devices such as printers. Until now the datasheet for these processors was only available for Marvell customers and partners under NDA, but last week, Marvell finally released the datasheet of the Armada 370 publicly, with no restriction, no registration, no NDA. The Armada 370 processor can already be found in several consumer grade products:

From now on, on the Marvell page (broken link removed) related to the Armada 3xx family, the Armada 370 Functional Specification (broken link removed) as well as the Armada 370 Hardware Specifications (broken link removed) can be found. While the Armada XP datasheet is not available at this time, it is worth mentioning that the vast majority of the peripherals are exactly the same between Armada 370 and Armada XP, so even Armada XP users will find useful information in this datasheet.

Bootlin is happy to see that Marvell is making more and more progress towards mainlining their kernel support and opening their datasheets publicly. We strongly believe that the openness of these datasheets will allow hobbyists and developers to improve the support for Armada 370 in the open-source ecosystem, be it in the Linux kernel, in bootloaders like U-Boot or Barebox or even in other projects.

2014 Q2 newsletter

Bootlin is happy to share some news about the latest training and contribution activities of the company.