Victoria Bazir
The work comes from the Asahi Linux project and consists of a 19-patch kernel series submitted by developer Sven Peter on August 30, 2026. The patches are currently under upstream review and have not been merged into Linux 7.3-rc1.
Linus Torvalds released Linux 7.3-rc1 on August 30, closing the merge window for the 7.3 cycle. The stable Linux 7.3 release is expected after several weeks of release-candidate testing.
Why Apple Silicon Needs a Custom Thunderbolt Driver
Apple Silicon does not expose USB4 and Thunderbolt hardware in the same way as conventional PC platforms.
Each USB4-capable USB-C port on M1 through M3 Macs uses an Apple Converged I/O, or ACIO, subsystem. ACIO contains:
- a Cortex-M3 coprocessor;
- the USB4 router;
- Apple's DART IOMMU;
- the Native Host Interface used by the Thunderbolt stack.
The main Apple SoC can access only a 16 MiB window of ACIO's memory-mapped I/O space while its coprocessor is running.
The new Linux driver manages the Apple-specific initialization process. When a USB-C connection is detected, it powers up ACIO, starts the RTKit coprocessor and exposes the DART and Native Host Interface components required by Linux.
From there, the hardware can connect to Linux's existing Thunderbolt software connection manager rather than requiring a completely separate Thunderbolt stack.
M1 to M3 Required Different Hardware Support
USB-C port management also changed across Apple Silicon generations. M1 through base M3 systems use Apple's CD3217, also known as ACE2, USB port controller.
M3 Pro and M3 Max introduced ACE3, which uses a different communication interface. Asahi Linux developers had to reverse-engineer this controller separately. By August 2026, Asahi's development stack had working USB 3.0 and Thunderbolt functionality across the M3 family.
The upstream patch series is intended to move the underlying Apple-specific support into the mainline Linux kernel.
What Works
The initial implementation supports USB 3 tunneling over USB4 and Thunderbolt XDomain connections. It is not yet complete Thunderbolt support. Additional functionality, including other protocol tunneling capabilities, still requires further development.
This is particularly relevant for PCI Express tunneling, one of Thunderbolt's major capabilities for devices such as high-speed storage, networking hardware and PCIe expansion equipment.
Linux 7.3 Status
Linux 7.3-rc1 was released on August 30, 2026. The Apple Silicon USB4/Thunderbolt patches were submitted around the same time but missed the 7.3 merge window. They therefore should not be described as a Linux 7.3 feature unless they are accepted through an exceptional late merge.
Linux 7.3-rc1 begins the stabilization phase of the kernel cycle. Major features are now largely frozen while developers test the kernel and fix regressions before the stable release.
Why Upstreaming Matters
Asahi Linux has spent years reverse-engineering Apple's undocumented or partially documented hardware interfaces.
Initially, many Apple Silicon drivers existed only in Asahi-specific kernel trees. Moving them upstream means the code becomes part of the official Linux kernel and can eventually be used directly by mainstream Linux distributions.
USB4 and Thunderbolt are significant additions because USB-C ports are the primary high-speed external I/O interface on modern Apple Silicon Macs.
The 19-patch series does not complete Thunderbolt support and is not yet part of Linux 7.3. But it establishes the kernel infrastructure required for native USB4 and Thunderbolt operation on M1, M2 and M3 systems — without an Apple-provided Linux driver.
Victoria Bazir
