Technical – Page 34

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

As 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:

Detailed agenda (PDF)
Slides (PDF)
Instructions for the practical labs (PDF),
Data needed for the practical labs (tarball)
The complete source code for those training materials is available in our Git repository at https://github.com/bootlin/training-materials/.

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

Call for participation for the FOSDEM Embedded developer room

The FOSDEM is by far the largest and most vibrant open-source event in Europe. With 5000+ participants, 400+ talks in just two days, a completely free entrance with no registration required, and many topics covered, it has become over the years a major meeting event of open-source developers.

The 2015 edition will take on January 31 and February 1st in Brussels. Like most years, a specific track dedicated to embedded systems is on the schedule, called the “Embedded Developer Room”. A call for participation has been published, and proposals are expected by December, 1st.

It is worth mentioning that the scope of the FOSDEM Embedded Developer Room goes much beyond Embedded Linux: it covers all types of embedded systems, including micro-controller based development, fun hacking or do-it-yourself projects, and much more. Looking at last year’s schedule of the Embedded Devroom is a good way of getting a feeling of the topics that are covered.

Also, FOSDEM has many other tracks that can be interesting to embedded Linux developers: last year there was a track about Tracing and debugging, a track about Memory and Storage, a track about Hardware, a developer room about Graphics, etc.

So, save the date, and join FOSDEM 2015 in Brussels!

Videos of XDC2014 and Kernel Recipes 2014

Recently, two interesting conferences took place in France: the X.org developer conference (in Bordeaux, October 8th-10th) and the Kernel Recipes conference (in Paris, September 25th-26th).

Both conferences have now published videos and slides of the different talks:

for the XDC 2014 conference, they are available in the program page
for the Kernel Recipes conference, they are available from the schedule page

It also means that the video of the talk given by Bootlin engineer Maxime Ripard about the support for Allwinner processors in the kernel is now available: video, slides.

https://www.youtube.com/watch?v=yJmZkzq651Q

Call for participation for the Embedded Linux Conference 2015

The Embedded Linux Conference Europe is just over that it’s already time to think about the Embedded Linux Conference 2015, which will take place on March 23-25 in San Jose, California.

The call for participation has been published recently, and interested speakers are invited to submit their proposals before January, 9th 2015. The notifications of whether your talk is accepted or not will be sent on January, 16th and the final schedule is planned to be published on January, 23th.

At Bootlin, we really would like to encourage developers who are working on interesting embedded Linux related projects to submit a talk about what they are doing: talking about a specific open-source project, feedback on some experience doing an embedded Linux based product, etc. The scope of topics covered by the Embedded Linux Conference is fairly broad, so do not hesitate to submit a proposal. Giving a talk at this conference is really a great way of getting feedback about what you’re doing, raising awareness about a particular project or issue, and generally meeting other developers interested in similar topics.

It is worth mentioning that for those people whose talk is accepted, the entrance ticket is free. For hobbyists working on their own on open-source projects, the Linux Foundation also has the possibility of funding travel to the conference.

Bootlin team back from ELCE and Linux Plumbers

As we announced in an earlier blog post, the entire Bootlin engineering team was at the Embedded Linux Conference Europe and Linux Plumbers Conference last week in Düsseldorf.

Bootlin engineering team at the Embedded Linux Conference Europe 2014. From left to right, Grégory Clement, Alexandre Belloni, Maxime Ripard, Antoine Ténart, Thomas Petazzoni, Boris Brezillon and Michael Opdenacker.

In addition to attending many talks, meeting developers of the embedded Linux community and therefore keeping us up-to-date with the most recent developments in this domain, we also gave a number of talks, for which the slides are now available:

The DRM/KMS Subsystem From a Newbie’s Point of View by Boris Brezillon. Slides available as PDF and source code.
Supporting a New ARM Platform: The Allwinner Example by Maxime Ripard. Slides available as PDF and source code.
Buildroot: A Deep Dive Into The Core by Thomas Petazzoni. Slides available as PDF and source code.
Two years of ARM SoC Support Mainlining: Lessons Learned by Thomas Petazzoni. Slides available as PDF and source code.

Maxime Ripard giving his Allwinner kernel talk

Thomas Petazzoni giving his Buildroot talk

At the social event, from left to right: Grégory Clement (Bootlin), Kevin Hilman (Linaro), Boris Brezillon (Bootlin), Maxime Ripard (Bootlin)

All the slides of the conference are also available on the event site of the Linux Foundation, and all talks have been video-recorded by the Linux Foundation so hopefully videos should become available in the near future.

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

Linux 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:

Xenomai 2.6.4 released, with Atmel SAMA5D3 support

At the end of September, the Xenomai project has announced the release of version 2.6.4. For the record, Xenomai is a hard real-time extension to the Linux kernel.

Amongst a number of bug fixes and improvements, this new release brings an interesting new feature to which Bootlin contributed: the support for the Atmel SAMA5D3. This means that Xenomai can now be used on platforms such as the Xplained SAMA5D3 and any other SAMA5D3 based platform. This work was done by Xenomai ARM maintainer Gilles Chanteperdrix, thanks to the testing and insights of Bootlin engineer Maxime Ripard.

Mainly, the change needed was to support the AIC5 interrupt controller used in SAMA5D3, which is different from the interrupt controller used on earlier AT91 processors. This change should also provide compatibility with the recently released SAMA5D4, though we haven’t tested this at this time, and Xenomai only provides its patch up to kernel 3.14, while SAMA5D4 support was only recently added to the mainline kernel.

This 2.6.4 Xenomai release also brings support for the 3.14 kernel version, through the corresponding I-Pipe patch.

There are also some other interesting Xenomai news: in early October, they have released the first release candidate of Xenomai 3, the next generation Xenomai architecture. And they also have a brand new and more modern website at xenomai.org.

Atmel SAMA5D4 support in the mainline Linux kernel

Atmel 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.