Linux 5.5 Feature Overview - Raspberry Pi 4 To New Graphics Capabilities To KUnit

Written by Michael Larabel in Software on 8 December 2019 at 06:39 PM EST. Page 1 of 1. 5 Comments.

Linux 5.5-rc1 is on the way to mirrors and with that the Linux 5.5 merge window is now over. Here is a look at the lengthy set of changes and new features for this next Linux kernel that will debut as stable in early 2020.

Among the many changes to find with Linux 5.5 are support for the Raspberry Pi 4 / BCM2711, various performance changes still being explored, support for reporting NVMe drive temperatures, a new Logitech keyboard driver, AMD HDCP support for content protection, wake-on-voice support from Chromebooks, the introduction of KUnit for unit testing the kernel, new RAID1 modes that are quite exciting for Btrfs, and much more. Below is a more detailed look based upon our original monitoring and reporting.


- Continued improvements for the AMD Arcturus Vega-based GPU bring-up.

- AMDGPU HDCP support for Raven Ridge and newer.

- AMDKFD support for the POWER architecture but the ROCm POWER user-space patches are still pending.

- Continued Intel Gen12 / Tiger Lake graphics bring-up along with initial Intel Jasper Lake support.

- The Allwinner Cedrus video decode driver now supports HEVC/H.265.

- AMD OverDrive overclocking for Navi GPUs.


- Btrfs RAID1C3/RAID1C4 modes that allow three and four copies of data with Btrfs' native RAID1 capabilities to offer more redundant support.

- Broadcom BCM2711 SoC support for the Raspberry Pi 4.

- KVM support for IBM POWER secure guests/VMs.

- KVM also now has nested 5-level page table support, Retpoline optimizations, and other Intel/AMD improvements for virtualization.

- SECCOMP support for RISC-V along with supporting the architecture's "M-Mode" and other enhancements.

- Support for the new Loongson 3A variant for this MIPS-based processor.

- Intel 5-level paging support is enabled by default for supporting greater virtual and physical address space.

- Significant changes to the Linux kernel's scheduler.

- Sanity checking of RdRand output in dealing with past buggy AMD CPUs / motherboard firmware.

- Late CPU microcode updates in parallel.

- Habana Labs preparing for future ASIC support.

- Working around an Arm Neoverse N1 bug.

- Support for vintage SGI Octane MIPS workstations.

Storage / File-Systems:

- NFS client support for cross-device offloaded copies for server-to-server transfers with NFSv4.2 server-side copy functionality.

- F2FS fixes.

- Many XFS changes.

- EXT4 now has direct I/O via iomap and FSCRYPT support for smaller block sizes.

- NVMe SSD drive temperatures are now conveniently exposed via sysfs rather than needing any special user-space components.

- A new HMEM driver for EFI specific purpose memory for cases like Intel Optane DC Persistent Memory.

- Microsoft exFAT file-system improvements for that driver that was added to staging last cycle.

Other Hardware:

- Support for toggling ASPM link states individually to offer better power-savings when a device may be connected where the driver by default is blocking ASPM.

- An Ice Lake USB power management improvement.

- The ability to boot the modem processor on the Snapdragon 835 SoC that is important not only for cellular but also WiFi support.

- A new Logitech keyboard driver.

- Another new hardware driver is the System76 ACPI Coreboot laptop driver. Also on the laptop front are Huawei support improvements.

- Thunderbolt improvements and officially deprecating the EEPROM driver highlight the char/misc changes.

- The new WFX WiFi driver for Silicon Labs WF200 ASICs.

- Wake-On-Voice support for select Chromebooks.

Security / Other:

- KUnit as an in-kernel unit testing means.

- The kernel concurrency sanitizer has been added for uncovering data race conditions.

- EFI RNG support as another source of entropy.

- Crypto improvements inspired by WireGuard's Zinc crypto API. These changes in turn will allow WireGuard to land finally with Linux 5.6.

- Linux 5.5 livepatching infrastructure now tracks the system state for better patch handling/compatibility.

- Dropping of the SYSCTL system call.

- Reworked AMD IOMMU driver code.

- Continued Year 2038 fixes.

- VMs on Microsoft Hyper-V can finally hibernate.

Stay tuned for Linux 5.5 benchmarks heating up in the days ahead.

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Michael Larabel

Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via