Linux 5.0 released, Bootlin contributions

Linux 5.0 was released two weeks ago by Linus Torvalds, and as it is now always the case, Bootlin has contributed a number of patches to this release. For an overview of the new features and improvements brought by Linux 5.0, we as usual recommend to read the LWN articles: merge window summary part 1, merge window summary part 2. The KernelNewbies.org page about this kernel release is also nicely documented.

In terms of contribution to Linux 5.0, according to the LWN statistics, Bootlin is the 12th contributing company by number of commits (261 commits), and 8th contributing company by number of changed lines. Bootlin engineer Maxime Ripard is 11th contributing developer by number of commits, and former Bootlin engineer Boris Brezillon is 12th contributing developer by number of commits, and 8th by number of changed lines. In this release, we are also happy to see numerous contributions from Paul Kocialkoswki who joined Bootlin in November 2018 after his internship working on the Linux kernel support for the Allwinner VPU.

Here are the main highlights of our contributions to Linux 5.0:

  • After 1.5 years of work, the I3C subsystem was finally merged and visible in drivers/i3c in your favorite kernel tree! We are proud to have pioneered the Linux kernel support for this new MIPI standard, which aims at providing an alternate solution to I2C and SPI, with interesting new features (higher speed, device discovery and enumeration, in-band interrupts, and more). See also our initial blog post about I3C, and our blog post about I3C being upstream.
  • In the RTC subsystem, Bootlin engineer and RTC kernel maintainer Alexandre Belloni reworked the way nvmem devices are handled, allowing for multiple nvmem devices to be registered for a single RTC as some have both battery-backed RAM and an on-chip EEPROM. devm_rtc_device_register() has been reimplemented to use the new registration path and is now deprecated. Its counterpart, devm_rtc_device_unregister() has been removed.
  • In the MTD subsystem
    • Boris Brezillon contributed a number of patches to the support for raw NAND mainly related to refactoring the subsystem. For example, some of the patches make the ->select_chip() of nand_chip a legacy hook, and removes its implementation from a number of drivers. All those patches do not bring any new feature per-se, but are part of a larger effort to clean up and modernize the MTD subsystem.
    • Boris Brezillon also contributed to the SPI NOR support a mechanism to fixup the information provided in the BFPT table of SPI NOR flashes. This is used to ensure that some Macronix SPI NOR flashes are properly recognized as supporting 4-byte opcodes.
  • Maxime Ripard contributed a number of improvements to the OV6540 camera sensor driver, especially to remove the hardcoded initialization sequence by a much more flexible initialization code, which allowed to support 60fps and more resolutions.
  • Maxime Ripard extended the PHY subsystem with two new functions, phy_configure() and phy_validate(), which allow to pass configuration details to PHY drivers. This was then used by Maxime to implement MIPI D-PHY drivers, which need a significant number of configuration parameters. See this commit and this commit for details. MIPI D-PHY are typically used in video display or capture HW pipelines.
  • As part of our work on RaspberryPi display support, Boris Brezillon contributed a number of fixs to the VC4 display controller driver.
  • For the support of Microchip MPU (Atmel) platforms, Alexandre Belloni migrated the AT91SAM9260, AT91SAM9261, AT91SAM9263, AT91SAM9RL, AT91SAM9x5, SAMA5D2 and SAMA5D4 platforms to the new clock Device Tree binding that he introduced in Linux 4.20.
  • For the support of Microchip UNG (formerly Microsemi) platforms, Alexandre Belloni added support for the Jaguar2 platform to the pinctrl driver already used for the Ocelot platform.
  • For the support of Allwinnner platforms:
    • Maxime Ripard did a huge amount of Device Tree cleanups and improvements, fixing DTC warnings, but generally making sure those Device Tree files are consistent.
    • Paul Kocialkowski implemented support for YUV planes in the Allwinner display controller driver. This allows to display a video decoded by the VPU directly into a display controller plane, and let the hardware compose it with other display planes, without CPU intervention.
    • Paul Kocialkowski enabled the VPU (for hardware-accelerated video decoding) on the Allwinner H5 and A64. This work was part of our crowdfunding campaign around the Allwinner VPU support.
  • For the support of Marvell platforms
    • Miquèl Raynal added support for suspend/resume to the SATA support on Armada 3720 (the SoC used for the popular EspressoBin platform), as part of a larger effort of bringing full suspend/resume support on Armada 3720
    • Miquèl Raynal implemented support for the thermal overheat interrupt on Armada 7K/8K.

Here is the detailed list of commits we contributed to Linux 5.0:

Author: Thomas Petazzoni

Thomas Petazzoni is CTO and embedded Linux and kernel engineer at Bootlin. He is a lead developer of Buildroot and also a contributor to the Linux kernel. More details...

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