Allwinner VPU support in mainline Linux status update (week 13)

While this week’s goal was set to supporting dmabuf in our Sunxi-Cedrus VAAPI implementation with GStreamer, progress was made on GStreamer support alone. The first milestone was displaying the video from videotestsrc, which produces a sample test output, to kmssink, which handles video output directly with DRM planes.

The Gstreamer pipeline for the test
The working result on display

This required specific adaptation for GStreamer to cope with the Allwinner DRM driver. More specifically, changes that allow the Allwinner DRM driver in kmspipe as well as devices that don’t sit on a PCI bus in gtreamer-vaapi were submitted. Patches to fix both these issues were sent for review earlier today and the first one was already accepted and merged. Thanks to Nicolas Dufresne for his help in the process!

On the VAAPI side, things are more complicated and a number of different areas of the sunxi-cedrus VAAPI backend had to be reworked. For instance, the slices constituting MPEG2 frames are not submitted in the same way by VLC and GStreamer. Buffers management is also done slightly differently between these two users of libVA. The net result is that a segmentation fault caused by a memory management mishaps is occurring with GStreamer and is still being investigated.

This week was also the occasion to dig into the partial reference code that Allwinner published in 2015 (to grasp a better understanding of the MPEG2 decoding process with the VPU) and start updating the register documentation on the linux-sunxi wiki, where some fields documented by the reference code were still marked as unknown. The Sunxi-Cedrus page was also updated to reflect the current status and effort. These resources will get updated as development happens. More precisely, we’d like to provide instructions to deploy this work, once it has reached a decent level of usability. Stay tuned for our next update!

Kickstarter for the Allwinner VPU Linux kernel support successfully funded!

Early February, we announced the launch of our first Kickstarter campaign, whose goal was to add support for the video decoding unit found in most Allwinner processors to the official Linux kernel.

We were very pleased to see that in just one day, enough companies and individuals participated to fund the main goal of the campaign, collecting more than 17,600 EUR. And now that the campaign is over since March 18, we are even more pleased, as we have reached a funding level sufficient to cover not only our main goal, but also our two first stretch goals.

Thanks to the participation of all those companies and individuals, we will be able to:

  1. Deliver our main goal, which we expect to deliver by the end of June 2018, which includes:
    • Making sure that the codec works on the older Allwinner SoCs that are still widely used: A10 (Cubieboard), A13 (A13-Olinuxino), A20 (Cubieboard 2, A20-Olinuxino), A33 (A33-Olinuxino, BananaPi M2-Magic), R8 (CHIP) and R16 (NES and Super NES classic). Support for the newer SoCs (H3, H5 and A64) requires more work, and is part of our first stretch goal below.
    • Polishing the existing MPEG2 decoding support to make it fully production ready.
    • Implementing H264 video decoding, since H264 is by far one of the most popular video codec.
    • Modifying the Allwinner display driver in order to be able to directly display the decoded frames instead of converting and copying those frames, which is very inefficient from a CPU consumption point of view
    • Providing a user-space library easy to integrate in the popular open-source video players
    • Upstreaming those changes to the official Linux kernel
  2. Deliver our two first stretch goals, which we expect to deliver by the end of 2018, which includes:
    • Supporting the newer Allwinner SoCs, such as the H3 (Most of the Orange Pis, Nano Pi M1, ..), H5 (Orange Pi PC2, NanoPi NEO2, …) and A64 (Pine64, BananaPi M64, …).
    • H265 video decoding support

Unfortunately, our third stretch goal, which consisted in adding support for H264 encoding was not reached, so we don’t know yet if we will have enough time to look into this topic.

Maxime Ripard and Paul Kocialkowski
Maxime Ripard and Paul Kocialkowski working on Allwinner VPU support

However, the work on the other topics has already started, with our intern Paul Kocialkowski has started to work since March 1st on this Allwinner VPU effort, and Maxime Ripard has started this week. We have already published, will continue to publish a report every week: week 10, week 11 and week 12. You can follow the progress of this project by reading our blog, our Twitter feed or the Kickstarter updates. You can also read the Sunxi-cedrus Wiki page to get all the details about this project and its progress.

Beyond the specific topic of the Allwinner VPU support, we are very happy to see that the model of funding upstream Linux kernel work through crowd-funding has worked. Most Kickstarter projects, in exchange for the participants contribution, provide to the participant a specific product (a book, a device) that only benefits to the contributor. Here, the result of this campaign will be shared freely with everybody, both Kickstarter contributors and non-contributors, and we’re proud to see that our experience has convinced numerous companies and individuals to support our project. Of course, we will be organizing in the near future the shipment of the t-shirts as well as the beer drinking sessions with Bootlin engineer Maxime Ripard.

To conclude, we would like to thank all our participants (we’re naming only the ones who baked at a level above 16 EUR, as above this level contributors are going to be mentioned in the CREDITS file, which clarifies their intent to be publicly named). First a number of companies supported our work: OrangePi, Libre Computer, neutis.io, FriendlyArm, Pine64, Olimex and of course a huge number of individuals: Abe Lacker, Adam Morris, Adam Oberbeck, Alerino Reis, Alex, Alexander A. Istomin, Alexander Kamm, Alexandru Nedel, Alex Kaplan, Amarpreet Minhas, André, Andreas, Andreas Färber, Andreas Rozek, Andre Przywara, Andrew Langley, Angel Rua Amo, Anssi Kolehmainen, Antony, Appreciation of Efforts, Aron Somodi, Artur Huhtaniemi, Atsushi Sasaki, Bastien Nocera, Bavay, Benjamin Glass, Benjamin Larsson, Ben Young, Bernard D’Havé, Bert Lindner, Bert Vermeulen, BESSIERES MARC, Biji-san, Bob Black, brot, Bruce Shipman, Butterkeks, Carla Sella, Carl Wall, Carsten Tolkmit, cbrocas, chae, Charlie Bruce, Christian Gnägi, Christian Pellegrin, Christian Stalp, Christophe Vaillot, Christoph Kröppl, Conan Kudo (ニール・ゴンパ), D1don, Dale Cousins, Daniel, Daniel Hrynczenko, Daniel Kulesz, Daniel Mühlbachler, David Pottage, David Willmore, defsy, Denis Bodor, DESSARD Guy, Dimitrios Bogiatzoules, Dominique Dumont, Doyle Young, Dubouil, Eelco Wesemann, eineki, Emil Karlson, Emmanuel Fusté, Erdem MEYDANLI, Eric des Courtis, Eric Jensen, Eric Koorn, Éric Périé, Erik, erikf, Evaryont, Fabian Korak, Felix Eickeler, Flo, Florian Beier, Florian Kempf, Frank, Frank van Kesteren, Frederir, G40, Gabor, Gabriel Ortiz, Garrett Gee, Georg Ottinger, Gerald Hochegger, Geralt, ghostpatch, Gianpaolo Macario, Giulio Benetti, Guenther Gassner, Guilhem, Guilhem Saurel, hackman, Hamish, Hanno Helge, Hans-Frieder Vogt, Heinz Thölecke, Henrik Kuhn, hook, Hugh Reynolds, Ian Daniher, iav, Inapplicable, Ingo Strauch, Ioan Rogers, Irvel Nduva, James, James Cloos, James Valleroy, jan koopmanschap, Jared Smith, Jari-Matti, Jarkko Pöyry, Jasper Horn, jean, Jean-Pierre Rivière, Jeffrey Sites, Jernej, Jerome Hanoteau, JK, John Kelley, Johnny Sorocil, Juanjo Marin, Jussi Pakkanen, Justin Ross, Karl Palsson, Kazım Rıfat Özyılmaz, Kean, Kevin Fowlks, Kevin Read, kicklix, Kiesel, Koen Kooi, Korbinian Probst, kratz00, Laurent GUERBY, Lee Donaghy, liushuyu, Logicite, luigi, Lukas Schauer, lzrmzz, Maksims Matjakubovs, Manuel, Marcel Sarge, Marcus Cooper, Mario Villarreal, Mark Dietzer, Markus Härer, Martijn Bosgraaf, mateuszkj, Mathias Brossard, mathieu, Matsumoto Kenichi, Matthew Zhang, Matthias, Matthias Lamm, Matt Mets, Maxime Brousse, Me, MESNIL Mikaël, Michael Gregorowicz, Michael Thalmeier, Michal Zatloukal, Mirko Vogt, mouren, N/A, naguirre, Neil Davenport, Nick Crasci, Nick Richards, Oleksij Rempel, oliver, Oliver Heyme, OSAKANA TARO, othiman, ozcoder, Pablo, Patrick, Paul Philippov, Paul Sykes, Per Larsson, Peter Gnodde, Peter Robinson, Philip-Dylan Gleonec, Phipli, Phoenix Chen, Pierce Lopez, Priit Laes, Prisma, Rainer Stober, Reignier, René Kliment, Reto Haeberli, Ricardo Salveti de Araujo, Richard Cote, Richard Ferlazzo, Riku Voipio, Robert Lukierski, Robert McQueen, roens, Rui Gu, Ryan Casey, Salvatore Bognanni, Samuel Frederick, Scott Devaney, Sebastian Krzyszkowiak, Sébastien DA ROCHA, Sergey Kopalkin, Sertac Tulluk, Shelby Cruver, Shervin Emami, SIMANCAS, Simon Josefsson, Spas Kyuchukov, ssam, Stan, Stanislav Bogatyrev, Stas, Stefan Bethke, Stefan Monnier, Steffen Elste, Stephan, Stephan Bärwolf, Stephen Kelly, Steven Seifried, Stokes Gresh, Sven Kasemann, SvOlli, Tarjei Solvang Tjønn, Tetsuyuki Kobayashi, Texier Pierre-jean, Thomas Monjalon, Thomas Samson, Tim Symossek, Todd Zebert, Tomas Virgl, tpc010, Tyler Style, Valentin Hăloiu, valhalla, Vasily Evseenko, Vitaly Shukela, Xavier Duret, Yannick Allard, Yves Serrano, Zoltan Herpai, ZotoPatate, zym060050.

Thanks everybody!

Allwinner VPU support in mainline Linux status update (week 12)

Following up on the work started last week, I finished implementing initial support for displaying the NV12-based tiled format (that we shall call MB32-tiled NV12). The frame, that was dumped from the VPU, is now correctly displayed on the screen (after adapting scaling coefficients that needed specific tweaking for this use case).

The result can be shown in the following picture, where our Big Buck Bunny has the right coloring:

Scaling is also supported for the tiled format, so the frame can be shown in full screen without resorting to software scaling.

A series of patches supporting these features was sent for review on the dri-devel mailing list, where it already got some feedback from Maxime Ripard (who maintains the sun4i DRM driver impacted by these patches) as well as other members of the community! There is already enough material to craft a second version and send it again for review.

Significant time was spent figuring out the DRM, KMS, DRI and X11 graphics pipeline (as well as specific details of the inner workings of display hardware) and how to properly integrate the overlay DRM plane with all this. We are evaluating all our options here before spending time on a specific implementation. Of course, we are trying to keep things as generic as possible and avoid introducing platform-specific code in userspace, but there are also challenges to overcome in this regard. On the Wayland side, things are looking much brighter as compositors such as Weston have support for managing hardware planes directly, so there should be less work required.

Finally, I started working on dmabuf support, that I am testing with gstreamer‘s kmssink, that allows outputting directly in a hardware plane. Once this work is ready, we’ll be able to get an idea of the performance of the VPU when it is not limited by software-based untiling and compositing. Stay tuned for updates in this direction!

Allwinner VPU support in mainline Linux status update (week 11)

After the initial submission of the Sunxi-Cedrus driver last week, I spent most of this week looking into the sun4i DRM (Direct Rendering Manager) driver. The driver is in charge of handling the display pipeline on Allwinner SoCs. Tight integration of the VPU and the display pipeline is required in order to achieve decent video playback performance. That is because the output format of the VPU is a 32×32 tiled format based on NV12, a YUV420 semi-planar format, with one plane for the Y component (luminance) and one plane for the interleaved UV components (chrominance). While NV12 is a standard format for video output, the tiling is rather specific to the VPU, so the frames have to be untiled before they can be used. This operation, when done in software, is rather slow. Moreover, software-based compositing of the decoded frames is also a bottleneck that impacts the overall performance.

In order to circumvent these issues, we will be using the display engine itself to untile the VPU output frames and show the untiled frames directly in a dedicated hardware plane, that is then composed with the primary plane. This requires several features and especially support for the display engine’s frontend, that has the required components to untile and decode the frames. Partial support for the frontend was recently contributed by Maxime Ripard and is on its way to landing in the mainline Linux kernel, providing a base for my VPU-related work. Maxime’s patches allow scaling hardware planes (among other things), a feature that will be very useful for scaling videos to the screen size in hardware rather than software (which is another major bottleneck for performance).

Support for untiling the VPU frames is approaching completion (luminance is correctly decoded while chrominance is not yet correctly handled).

Decoding the MB32 tiled format with sun4i-drm

Once the frames are properly shown on screen, it’ll be time to make sure that dmabuf works as expected, which will allow us to send buffers from the VPU to the display engine without any copy, thus improving performance.

We should be making good progress on this topic over the upcoming week and start contributing patches to the sun4i DRM driver, so stay tuned for our next status update!

Allwinner VPU support in mainline Linux status update (week 10)

Just over a week ago, I started my internship focused on adding upstream Linux kernel support for the Allwinner VPU at Bootlin’s Toulouse office. The team has been super-friendly and very helpful to help me get settled and I’m definitely happy about moving to Toulouse for the occasion!

This first week of work was focused on studying and rebasing the work done by Florent Revest a year and a half ago. As a main development target, I went for an A33-based board, the SinA33 from Sinlinx. Florent’s patches for the sunxi-cedrus driver were rebased against the latest release candidate version of Linus’ tree, v4.16-rc4.

VPU decoding with Cedrus on the Sinlinx A33

The driver was then adapted to use the latest version of the V4L2 request API, a crucial piece of plumbing needed to provide coherency between setting specific controls for the media stream and the input/output buffers that these controls are related to. A few bugs needed fixing along the way, in order to avoid memory corruptions (use-after-free) and to properly schedule the VPU to run when a request is submitted. With these fixes the driver was ready, so it was sent for review on the linux-media mailing list. On the userspace side, the cedrus-specific libva was also updated to use the latest version of the request API.

The next step in the pipeline is to use a common buffer for the VPU’s decoded frame and the display controller’s plane, using dmabuf. This should bring a significant performance improvement and eventually allow for hardware-based scaling when decoding videos through the standard DRM/KMS interfaces. However, this requires adding support for the specific format used by the VPU (a multiplanar NV12 format with 32×32 tiles) into the display controller code.