In partnership with ST, we are organizing on February 9, 2021, a free webinar entitled “Device Tree 101”.
The Device Tree has been adopted for the ARM 32-bit Linux kernel support almost a decade ago, and since then, its usage has expanded to many other CPU architectures in Linux, as well as bootloaders such as U-Boot or Barebox. Even though Device Tree is no longer a new mechanism, developers coming into the embedded Linux world often struggle to understand what Device Trees are, what is their syntax, how they interact with the Linux kernel device drivers, what Device Tree bindings are, and more. This webinar will offer a deep dive into the Device Tree, to jump start new developers in using this description language that is now ubiquitous in the vast majority of embedded Linux projects. This webinar will be illustrated with numerous examples applicable to the STM32MP1 MPU platforms, which make extensive usage of the Device Tree.
This webinar will take place on February 9, 2021, and is proposed at two different times during the day: at 10 AM CET (UTC+1) and 5 PM CET (UTC+1). The duration of the webinar is 1 hours and 30 minutes. Registration is free at https://www.eventbrite.com/e/135964923747. The webinar itself will be hosted as a Youtube Live stream, which will allow participants to ask questions in the chat during the webinar.
The trainer for this webinar is Thomas Petazzoni, Bootlin’s CTO. Thomas is the author of the popular « Device Tree for Dummies » talk given in 2014 and which helped numerous embedded Linux developers get started with the Device Tree. Thomas has contributed over 900 patches to the official Linux kernel, mainly around ARM hardware platform support. He is also the co-maintainer of the Buildroot open-source project.
Since 2017, Bootlin is freely providing ready-to-use pre-built cross-compilation toolchains at https://toolchains.bootlin.com/. We are now providing over 150 toolchains, for a wide range of CPU architectures, covering the glibc, uClibc-ng and musl C libraries, with up-to-date gcc, binutils, gdb and C library support.
We recently contributed an improvement to Buildroot that allows those toolchains to very easily be used in Buildroot configurations: the Bootlin toolchains are now all known by Buildroot as existing external toolchains, next to toolchains from other vendors such as ARM, Synopsys and others.
If you are building a Buildroot system for a CPU architecture variant that has a matching toolchain available from bootlin.toolchains.com, then Bootlin toolchains will naturally show up in the Toolchain sub-menu, when the selected Toolchain type is External toolchain. For example, if the selected CPU architecture is ARM little endian Cortex-A9, with VFP you will see:
Once Bootlin toolchains is selected, a new sub-option Bootlin toolchain variant appears, which allows to choose between the different toolchains applicable to the selected CPU architecture:
This hopefully should make Bootlin toolchains easier to use for Buildroot users.
Internally, this support for Bootlin toolchains in Buildroot is generated and updated using the support/scripts/gen-bootlin-toolchains script. In addition to making the toolchains available to the user, it allows generates some Buildroot test cases for each toolchain, so that each of those configuration is tested by Buildroot continuous integration, see support/testing/tests/toolchain/test_external_bootlin.py.
Linux 5.10 was released a few weeks ago, and while 5.11-rc2 is already out, it’s still time to look at what Bootlin contributed to the 5.10 kernel. As usual, for a broad overview of the major changes in 5.10, we recommend reading the LWN articles: 5.10 merge window part 1, the rest of the 5.10 merge window, or the 5.10 KernelNewbies page.
Overall, Bootlin contributed 78 patches to this kernel release, in the following areas:
Alexandre Belloni did a number of improvements in the support of Microchip ARM platforms: device tree updates, code cleanups, etc.
Alexandre Belloni added a new rv3032 RTC driver and did some improvements to the r9701 RTC driver.
Miquèl Raynal implemented a significant rework of how ECC engines are handled in the MTD subsystems, so that ECC engines can be used not just for parallel NANDs but also for SPI NANDs. See also the talk that Miquèl gave at the Embedded Linux Conference Europe on this topic: slides and video.
Miquèl Raynal contributed a few improvements to the tlv320aic32x4 audio codec driver.
Paul Kocialkowski made some small improvements, one in the OV5640 camera sensor driver, and one in the Rockchip DRM driver.
Thomas Petazzoni implemented a performance improvement in the max310x driver, used for SPI-connected UART controllers.
In addition to these code contributions, we also contribute by having several of our engineers be maintainers of a few subsystems of the Linux kernel. As part of this:
Miquèl Raynal reviewed and merged 47 patches touching the MTD subsystem he co-maintains with other kernel developers.
Alexandre Belloni reviewed and merged 42 patches touching either the Microchip ARM or MIPS platforms, or the RTC subsystem.
Grégory Clement reviewed and merged 2 patches touching the Marvell ARM/ARM64 platform support.
Since December 1st, 2020, we’re happy to have in our team an additional engineer, Thomas Perrot, who joined our office in Toulouse, France.
Thomas brings 6+ years of experience working on embedded Linux systems, during which he worked at Intel on Android platforms, and then at Sigfox on the base stations for Sigfox’s radio network. Thomas has experience working with Linux on x86-64, ARM and ARM64 platforms, with a wide range of skills: bootloader development, Linux kernel and driver development, Yocto integration, OTA updates. Thomas was also deeply involved in the strong security aspects of Sigfox base stations, with secure boot and measured boot, TPM, integrity measurement, etc. At Sigfox, Thomas was involved in all steps of the product life-cycle, from the design phase all the way to the in-field deployment, update and maintenance. Last but not least, Thomas is a Linux technologist and a free software enthusiast, who hacks some open source hardware projects on his free time. See also Thomas page on our website and his LinkedIn profile.
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
The 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:
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
As 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
CSI-2
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
As 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.
In 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.
In 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.
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.
In 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.
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.
Conclusion
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.
