Usb4 devices are not expected to be available until later this year, but the Linux 5.6 kernel has added initial support for USB4. Supporting USB4 in Linux 5.6 is a much-anticipated feature, and it’s really implemented now. The Linux kernel mailing list shows that initial support for USB4 has been added to Linux Kernel 5.6-rc1 and entered the kernel mainline.
The USB4 specification was announced last September, and the Linux kernel is so quick to provide support for USB4 because USB4 is based on Thunderbolt 3. Therefore, enabling support for USB4 in the Linux kernel is largely based on existing Thunderbolt Linux code.
In addition, Intel’s large open source team provided the linux 5.6 kernel with the initial USB4 code, which also transferred the Kconfig option from Thunderbolt to the USB4 naming scheme.
In addition to adding support for USB4 in the Linux 5.6 kernel, other USB/Thunderbolt-related work includes separate DisplayPort standby mode devices in Type-C code that can handle USB wake-up events from USB devices (USB Wake-On), a large number of NVIDIA Tegra USB updates, support for mediatek MUSB controllers, support for USB 3.x tunnels in Thunderbolt, and various other support improvements.
The complete list of USB improvements to the Linux 5.6 kernel comes from this PR, which has been merged into the main line.