On-going Bootlin contributions to the Video4Linux subsystem: camera, camera sensors, video encoding

Over the past years, we have been more and more involved in projects that have significant multimedia requirements. As part of this trend, 2020 has lead us to work on a number of contributions to the Video4Linux subsystem of the Linux kernel, with new drivers for camera interfaces, camera sensors, video decoders, and even HW-accelerated video encoding. In this blog post, we propose to summarize our contributions and their status on the following topics:

  • Rockchip PX30, RK1808, RK3128 and RK3288 camera interface driver
  • Allwinner A31, V3s/V3/S3 and A83T MIPI CSI-2 support for the camera interface driver
  • Omnivision OV8865 camera sensor driver
  • Omnivision OV5648 camera sensor driver
  • TW9900 PAL/NTSC video decoder driver
  • Rockchip HW-accelerated H264 video encoding

Rockchip camera interface

Rockchip camera interfaceThe Rockchip ARM processors are known to have very good support in the upstream Linux kernel. However, one area where the support was lacking is in the support of the camera interface used by those SoCs. And it turns out that Bootlin engineer Maxime Chevallier has worked precisely on this topic throughout 2020: the development and upstreaming of the rkvip driver, a Video4Linux driver for the Rockchip camera interface. While the work was done and tested on a Rockchip PX30 platform, the same camera interface is used on RK1808, RK3128 and RK3288.

Several iterations of the driver have been posted on the linux-media mailing list, with the latest iteration, version 5, posted on December 29, 2020:

Maxime Chevallier (3):
  media: dt-bindings: media: Document Rockchip VIP bindings
  media: rockchip: Introduce driver for Rockhip's camera interface
  arm64: dts: rockchip: Add the camera interface description of the PX30

 .../bindings/media/rockchip-vip.yaml          |  101 ++
 arch/arm64/boot/dts/rockchip/px30.dtsi        |   12 +
 drivers/media/platform/Kconfig                |   15 +
 drivers/media/platform/Makefile               |    1 +
 drivers/media/platform/rockchip/vip/Makefile  |    3 +
 drivers/media/platform/rockchip/vip/capture.c | 1146 +++++++++++++++++
 drivers/media/platform/rockchip/vip/dev.c     |  331 +++++
 drivers/media/platform/rockchip/vip/dev.h     |  203 +++
 drivers/media/platform/rockchip/vip/regs.h    |  260 ++++
 9 files changed, 2072 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/media/rockchip-vip.yaml
 create mode 100644 drivers/media/platform/rockchip/vip/Makefile
 create mode 100644 drivers/media/platform/rockchip/vip/capture.c
 create mode 100644 drivers/media/platform/rockchip/vip/dev.c
 create mode 100644 drivers/media/platform/rockchip/vip/dev.h
 create mode 100644 drivers/media/platform/rockchip/vip/regs.h

We’re hoping to get this driver merged soon, as we have now addressed the feedback that was received through the 5 iterations the patch series as gone through. It should be noted that for now it only supports the parallel BT656 interface as this is what we needed for our current project, we are definitely able to extend it to support MIPI CSI2 as well if you’re interested!

It should be noted that as a result of this work, Maxime Chevallier also prepared and delivered a talk From a video sensor to your display which was given at the Embedded Linux Conference Europe 2020. See the slides and video.

Allwinner MIPI CSI2 camera interface

Allwinner MIPI CSI2As part of an internship in 2020 and then a customer project, Bootlin intern Kévin L’Hôpital and Bootlin engineer Paul Kocialkowski worked on extending the Allwinnera camera interface support with support for MIPI CSI2 cameras. In fact, this addition was done to two Allwinner camera interface drivers: the sun6i driver which is used on Allwinner A31 and V3s/V3/S3, and the sun8i-a83t, which is used on the Allwinner A83T.

Through a fairly long 15 patches patch series, support for MIPI CSI2 is added to both camera interface controllers. We have tested both with Omnivision sensors, which are described below.

The series is currently in its third iteration, which was posted by Paul Kocialkowski on December 11, 2020 on the linux-media mailing list:

Paul Kocialkowski (15):
  docs: phy: Add a part about PHY mode and submode
  phy: Distinguish between Rx and Tx for MIPI D-PHY with submodes
  phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI
  media: sun6i-csi: Use common V4L2 format info for storage bpp
  media: sun6i-csi: Only configure the interface data width for parallel
  dt-bindings: media: sun6i-a31-csi: Add MIPI CSI-2 input port
  media: sun6i-csi: Add support for MIPI CSI-2 bridge input
  dt-bindings: media: Add A31 MIPI CSI-2 bindings documentation
  media: sunxi: Add support for the A31 MIPI CSI-2 controller
  ARM: dts: sun8i: v3s: Add nodes for MIPI CSI-2 support
  MAINTAINERS: Add entry for the Allwinner A31 MIPI CSI-2 bridge
  dt-bindings: media: Add A83T MIPI CSI-2 bindings documentation
  media: sunxi: Add support for the A83T MIPI CSI-2 controller
  ARM: dts: sun8i: a83t: Add MIPI CSI-2 controller node
  MAINTAINERS: Add entry for the Allwinner A83T MIPI CSI-2 bridge

 .../media/allwinner,sun6i-a31-csi.yaml        |  88 ++-
 .../media/allwinner,sun6i-a31-mipi-csi2.yaml  | 149 ++++
 .../media/allwinner,sun8i-a83t-mipi-csi2.yaml | 147 ++++
 Documentation/driver-api/phy/phy.rst          |  18 +
 MAINTAINERS                                   |  16 +
 arch/arm/boot/dts/sun8i-a83t-bananapi-m3.dts  |   2 +-
 arch/arm/boot/dts/sun8i-a83t.dtsi             |  26 +
 arch/arm/boot/dts/sun8i-v3s.dtsi              |  67 ++
 drivers/media/platform/sunxi/Kconfig          |   2 +
 drivers/media/platform/sunxi/Makefile         |   2 +
 .../platform/sunxi/sun6i-csi/sun6i_csi.c      | 165 +++--
 .../platform/sunxi/sun6i-csi/sun6i_csi.h      |  58 +-
 .../platform/sunxi/sun6i-csi/sun6i_video.c    |  53 +-
 .../platform/sunxi/sun6i-csi/sun6i_video.h    |   7 +-
 .../platform/sunxi/sun6i-mipi-csi2/Kconfig    |  12 +
 .../platform/sunxi/sun6i-mipi-csi2/Makefile   |   4 +
 .../sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c   | 590 ++++++++++++++++
 .../sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.h   | 117 ++++
 .../sunxi/sun8i-a83t-mipi-csi2/Kconfig        |  11 +
 .../sunxi/sun8i-a83t-mipi-csi2/Makefile       |   4 +
 .../sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.c    |  92 +++
 .../sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.h    |  39 ++
 .../sun8i_a83t_mipi_csi2.c                    | 657 ++++++++++++++++++
 .../sun8i_a83t_mipi_csi2.h                    | 197 ++++++
 drivers/phy/allwinner/phy-sun6i-mipi-dphy.c   | 164 ++++-
 drivers/staging/media/rkisp1/rkisp1-isp.c     |   3 +-
 include/linux/phy/phy-mipi-dphy.h             |  13 +
 27 files changed, 2581 insertions(+), 122 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml
 create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun8i-a83t-mipi-csi2.yaml
 create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/Kconfig
 create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/Makefile
 create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
 create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.h
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/Kconfig
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/Makefile
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.c
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.h
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
 create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.h

Here as well, the patch series has gone through a number of iterations, with significant reshaping to take into account the comments and feedback of other kernel developers and maintainers, so we hope to be near the point where it can be merged.

Omnivision OV8865 camera sensor driver

OV8865 block diagramAs part of his internship at Bootlin in 2020, Kévin L’Hôpital implemented a driver for the OV8865 camera sensor, connected over MIPI CSI2 to an Allwinner A83T platform. This OV8865 was then taken by Bootlin engineer Paul Kocialkowski, who did additional rework and polishing.

We are currently at the 4th iteration of this driver, which has been posted on December 11, 2020, and it has now been accepted and submitted to the V4L maintainer in a pull request.

Kévin L'hôpital (1):
  ARM: dts: sun8i: a83t: bananapi-m3: Enable MIPI CSI-2 with OV8865

Paul Kocialkowski (2):
  dt-bindings: media: i2c: Add OV8865 bindings documentation
  media: i2c: Add support for the OV8865 image sensor

 .../bindings/media/i2c/ovti,ov8865.yaml       |  124 +
 arch/arm/boot/dts/sun8i-a83t-bananapi-m3.dts  |  102 +
 drivers/media/i2c/Kconfig                     |   13 +
 drivers/media/i2c/Makefile                    |    1 +
 drivers/media/i2c/ov8865.c                    | 2981 +++++++++++++++++
 5 files changed, 3221 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml
 create mode 100644 drivers/media/i2c/ov8865.c

Omnivision OV5648 camera sensor driver

OV5648 block diagramIn addition to the work done by Bootlin intern Kévin L’Hôpital on OV8865 with Allwinner A83T, Paul Kocialkowski worked on OV5648 with Allwinner V3s, also connected over MIPI CSI2. This work results in a driver for the OV5648 camera sensor, which Paul has submitted to the linux-media mailing list.

This driver is now in is 5th iteration, posted on December 11, 2020, and it has now been accepted and submitted to the V4L maintainer in a pull request.

Paul Kocialkowski (2):
  dt-bindings: media: i2c: Add OV5648 bindings documentation
  media: i2c: Add support for the OV5648 image sensor

 .../bindings/media/i2c/ovti,ov5648.yaml       |  115 +
 drivers/media/i2c/Kconfig                     |   13 +
 drivers/media/i2c/Makefile                    |    1 +
 drivers/media/i2c/ov5648.c                    | 2638 +++++++++++++++++
 4 files changed, 2767 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/media/i2c/ovti,ov5648.yaml
 create mode 100644 drivers/media/i2c/ov5648.c

TW9900 PAL/NTSC video decoder driver

TW9900In addition to working on the Rockchip camera interface driver, Maxime Chevallier has also worked on a driver for the TW9900 PAL/NTSC video decoder. This chip from Renesas, takes as input an analog PAL or NTSC signal, digitizes it and outputs it on a parallel BT656 interface, which in our case was connected to a Rockchip PX30 platform.

Maxime posted the third iteration of the patch series adding this driver on December 22, 2020 on the linux-media mailing list.

Maxime Chevallier (3):
  dt-bindings: vendor-prefixes: Add techwell vendor prefix
  media: dt-bindings: media: i2c: Add bindings for TW9900
  media: i2c: Introduce a driver for the Techwell TW9900 decoder

 .../devicetree/bindings/media/i2c/tw9900.yaml |  60 ++
 .../devicetree/bindings/vendor-prefixes.yaml  |   2 +
 MAINTAINERS                                   |   6 +
 drivers/media/i2c/Kconfig                     |  11 +
 drivers/media/i2c/Makefile                    |   1 +
 drivers/media/i2c/tw9900.c                    | 617 ++++++++++++++++++
 6 files changed, 697 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/media/i2c/tw9900.yaml
 create mode 100644 drivers/media/i2c/tw9900.c

Rockchip HW-accelerated H264 video encoding

In 2018 and thanks to success of the crowd-funding campaign we ran back then, Bootlin engineer Paul Kocialkowski pioneered support for stateless video decoders in the Linux kernel, with a first driver supporting MPEG2, H264 and H265 HW-accelerated video decoding on Allwinner platforms.

Rockchip video encoderIn 2020, Paul was tasked to work on HW-accelerated H264 video encoding for Rockchip platforms, which also use a stateless video encoder. Of course, Paul took the same approach of going towards an upstream-acceptable solution rather than relying on out-of-tree and vendor-specific solutions provided by Rockchip.

Paul has been able to implement a working solution for one of our customers, and while the result is not yet in a shape where it can be submitted upstream, Paul has presented its result at the Embedded Linux Conference Europe 2020: the slides and video. The kernel code is available at https://github.com/bootlin/linux/tree/hantro/h264-encoding while the user-space code is available at https://github.com/bootlin/v4l2-hantro-h264-encoder.

As explained in Paul’s talk, this is not fully ready for upstream, as lots of discussions are needed on the user-space APIs, especially around the topic of rate control.

If you are interested in having this work fully available in the upstream Linux kernel, please contact us. We are looking for additional funding and support to push this completely upstream.


As can be seen from the numerous topics covered in this blog post, Bootlin has significant experience with the Video4Linux subsystem, and is able to both implement support for new hardware, extend the Video4Linux subsystem if needed, and contribute drivers and changes to the official Linux kernel.

Wrapping up the Allwinner VPU crowdfunded Linux driver work

Back in early 2018, Bootlin started a crowd-funding campaign to fund the development of an upstream Linux kernel driver for the VPU found in Allwinner processors. Thanks to the support from over 400 contributors, companies and individuals, we have been able to bring support for hardware-accelerated video decoding in the mainline Linux kernel for Allwinner platforms.

From April 2018 to end of 2019, Paul Kocialkowski and Maxime Ripard at Bootlin worked hard on developing the driver and getting it accepted upstream, as well as developing the corresponding user-space components. We regularly published the progress of our work on this blog.

As of the end of 2019, we can say that all the goals defined in the Kickstarter have been completed:

  • We have an upstream Linux kernel for the Allwinner VPU, in drivers/staging/media/sunxi/cedrus, which supports MPEG2 decoding (since Linux 4.19), H264 decoding (since Linux 5.2) and H265 decoding (will be in the upcoming Linux 5.5)
  • We have a user-space VA-API implementation called libva-v4l2-request, and which allows to use any Linux kernel video codec based on the request API.
  • We have enabled the Linux kernel driver on all platforms we listed in our Kickstarter campaign: A13/A10S/A20/A33/H3 (since Linux 4.19), A64/H5 (since Linux 4.20), A10 (since Linux 5.0) and H6 (since Linux 5.1, contributed by Jernej Skrabec)

This means that the effort that was funded by the Kickstarter campaign is now over, and from now on, we are operating in maintenance mode regarding the cedrus driver: we are currently not actively working on developing new features for the driver anymore.

The Cedrus Linux driver in action

Of course, there are plenty of additional features that can be added to the driver: support for H264 encoding, support for high-profile H264 decoding, support for other video codecs. Bootlin is obviously available to develop those additional features for customers, do not hesitate to contact us if you are interested.

Overall, we found this experience of funding upstream Linux kernel development through crowd-funding very interesting and we’re happy to have been successful at delivering what was promised in our campaign. Looking at the bigger picture, the Linux userspace API for video decoding with stateless hardware codecs in V4L2 has been maturing for a while and is getting closer and closer to being finalized and declared a stable kernel API: this project has been key in the introduction of this API, as cedrus was the first driver merged to require and use it. Additional drivers are appearing for other stateless decoding engines, such as the Hantro G1 (found in Rockchip, i.MX and Microchip platforms) or the rkvdec engine. We are of course also interested in working on support for these VPUs, as we have gained significant familiarity with all things related to hardware video decoding during the cedrus adventure.

Back from ELCE 2019: our talks videos, slides, and more!

With 8 engineers participating to the Embedded Linux Conference Europe, almost the entire Bootlin engineering team took part to the conference. As usual, we not only attended the event, but also contributed by giving a total of 5 talks and 2 tutorials, for which we’re happy to share below the videos and slides. Also, as part of this conference, Bootlin CTO Thomas Petazzoni received an award for his contribution to the conference.

Buildroot, what’s new ?

Talk given by Thomas Petazzoni, slides in PDF and slides source code.

Timing boot time reduction techniques

Talk given by Michael Opdenacker, slides in PDF, slides source code.

Integrating hardware-accelerated video decoding with the display stack

Talk given by Paul Kocialkowski, slides in PDF, slides source code.

RTC subsystem, recent changes and where it is heading

Talk given by Alexandre Belloni, slides in PDF, slides source code.

Flash subsystems status update

Talk given by Miquèl Raynal (from Bootlin) and Richard Weinberger (from sigma star gmbh), slides in PDF, slides source code.

Offloading network traffic classification to hardware

Talk given by Maxime Chevallier, slides in PDF, slides source code.

Introduction to Linux Kernel driver programming

Tutorial given by Michael Opdenacker, slides in PDF, slides source document. The video is not yet available, but should be published in the future.

Introduction to the Buildroot embedded Linux build system

Tutorial given by Thomas Petazzoni, slides in PDF, slides source code. The video is not yet available, but should be published in the future.

Award to Thomas Petazzoni

During the traditional closing game of the conference, we were really happy to have Bootlin’s CTO Thomas Petazzoni called on stage, to receive from the hands of Tim Bird, an award for his continuous 11 year participation to the conference, with 24 presentations given, one keynote and for the past two years, participation to the conference program committee. We are honored and proud by this recognition of Thomas contribution to the conference.

Thomas Petazzoni receives ELCE conference award

Thomas Petazzoni receives ELCE conference award

Thomas Petazzoni receives ELCE conference award

Slides and videos from the Embedded Linux Conference Europe 2016

Last month, the entire Bootlin engineering team attended the Embedded Linux Conference Europe in Berlin. The slides and videos of the talks have been posted, including the ones from the seven talks given by Bootlin engineers:

  • Alexandre Belloni presented on ASoC: Supporting Audio on an Embedded Board, slides and video.
  • Boris Brezillon presented on Modernizing the NAND framework, the big picture, slides and video.
  • Boris Brezillon, together with Richard Weinberger from sigma star, presented on Running UBI/UBIFS on MLC NAND, slides and video.
  • Grégory Clement presented on Your newer ARM64 SoC Linux check list, slides and video.
  • Thomas Petazzoni presented on Anatomy of cross-compilation toolchains, slides and video.
  • Maxime Ripard presented on Supporting the camera interface on the C.H.I.P, slides and video.
  • Quentin Schulz and Antoine Ténart presented on Building a board farm: continuous integration and remote control, slides and video.

Support for the Allwinner VPU in the mainline Linux kernel

Over the last few years, and most recently with the support for the C.H.I.P platform, Bootlin has been heavily involved in initiating and improving the support in the mainline Linux kernel for the Allwinner ARM processors. As of today, a large number of hardware features of the Allwinner processors, especially the older ones such as the A10 or the A13 used in the CHIP, are usable with the mainline Linux kernel, including complex functionality such as display support and 3D acceleration. However, one feature that was still lacking is proper support for the Video Processing Unit (VPU) that allows to accelerate in hardware the decoding and encoding of popular video formats.

During the past two months, Florent Revest, a 19 year old intern at Bootlin worked on a mainline solution for this Video Processing Unit. His work followed the reverse engineering effort of the Cedrus project, and this topic was also listed as a High Priority Reverse Engineering Project by the FSF.

The internship resulted in a new sunxi-cedrus driver, a Video4Linux memory-to-memory decoder kernel driver and a corresponding VA-API backend, which allows numerous userspace applications to use the decoding capabilities. Both projects have both been published on Github:

Currently, the combination of the kernel driver and VA-API backend supports MPEG2 and MPEG4 decoding only. There is for the moment no support for encoding, and no support for H264, though we believe support for both aspects can be added within the architecture of the existing driver and VA-API backend.

A first RFC patchset of the kernel driver has been sent to the linux-media mailing list, and a complete documentation providing installation information and architecture details has been written on the linux-sunxi’s wiki.

Here is a video of VLC playing a MPEG2 demo video on top of this stack on the Next Thing’s C.H.I.P: