USB4 devices are expected to come out until later this year, but before Linux 5.6 kernel has been added initial support for the USB4.
Support USB4 is much anticipated features in Linux 5.6, and now indeed been achieved. Linux kernel mailing list shows initial support for USB4 has been added to the Linux Kernel 5.6-rc1, go to the mainline kernel.
USB4 specifications announced in September last year , Linux kernel is so quickly provide support for USB4 because USB4 based Thunderbolt 3. So, to enable the Linux kernel support for USB4 largely based on existing Thunderbolt Linux code.
In addition, Intel huge revenue team also provided initial USB4 code for the Linux 5.6 kernel, which will support USB4 Kconfig options transferred from Thunderbolt to USB4 naming scheme.
Linux 5.6 kernel in addition to adding support for USB4 the, other, and USB / Thunderbolt related work further comprises a support separate DisplayPort standby mode apparatus Type-C code, can handle USB from the USB device to S2 wake-up event (USB the Wake -On), a large number of NVIDIA Tegra USB update, couplet technology support MUSB controller, support for the Thunderbolt USB 3.x tunnel, and improvements to various other USB support.
USB on the Linux 5.6 kernel to improve the complete list table from PR , the PR has been merged into the mainline.