Linux 6.1 Thunderbolt Networking To Support USB4 End-To-End Flow Control

Written by Michael Larabel in Linux Networking on 1 September 2022 at 05:20 AM EDT. 11 Comments
One of the interesting capabilities with Thunderbolt and now USB4 that is seemingly not too widely used is for networking between systems. The Linux kernel for the past half-decade already has offered a Thunderbolt networking driver for networking between hosts with Thunderbolt cables. The latest improvement on this front is now supporting USB4's end-to-end flow control mode.

The Linux Thunderbolt/USB4 networking driver started out with targeting the Apple ThunderboltIP protocol, which has evolved into USB4NET. Intel engineers have been maintaining this network driver as with much of the Thunderbolt Linux software stack.

The Thunderbolt/USB4 networking driver for Linux is now enabling support for end-to-end flow control support, which is part of the spec and supported by Intel's controllers. The end-to-end flow control mode avoids dropping of packets when there is not enough hardware receiver buffers.

More details on the end-to-end flow control mode can be found via this USB IF presentation.

This quality of service improvement for the USB4/Thunderbolt Linux networking driver has been queued in net-next ahead of the Linux 6.1 merge window.
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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

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