USB4 technology, based on the Thunderbolt 3 protocol, provides significant improvements in data transfer speeds and device compatibility. Linux Kernel 6.5 introduced initial support for USB4 v2, making it easier for users to utilize this advanced connectivity standard. If you're running Kernel 6.5 or later, you can quickly determine whether your system supports USB4 and enable it effectively.

Method 1: Checking USB4 Compatibility via Command Line

Step 1: First, ensure you're running Linux Kernel 6.5 or newer. Open your terminal and enter the following command to check your current kernel version:

uname -r

If your kernel version is lower than 6.5, you'll need to upgrade to Kernel 6.5 or newer to utilize USB4 support. You can upgrade your kernel using your distribution's package manager or by manually installing the latest mainline kernel.

Step 2: To verify if your hardware supports USB4, use the lsusb -t command. Run:

lsusb -t

This command displays a hierarchical view of USB devices and their connected bus speeds. USB4 devices typically show speeds of 20 Gbps (20000M) or higher. If you see a speed of 20000M or more, your system hardware supports USB4.

If you only see 10000M (10 Gbps) or lower, your hardware might not fully support USB4. Keep in mind, however, that USB4 specification does not strictly mandate speeds above 10 Gbps; some implementations might still be labeled USB4 but only support 10 Gbps.

Method 2: Identifying USB4 Support Through Sysfs Interface

Step 1: Another reliable method to confirm USB4 support is through the sysfs interface. Navigate to the Thunderbolt device directory:

cd /sys/bus/thunderbolt/devices/

Step 2: List the contents to check if USB4 is recognized:

ls

If the directory lists devices with names like usb4_portX, your system has recognized USB4-capable ports. Additionally, check the security and iommu_dma_protection attributes to ensure proper protection and security levels for USB4 devices:

cat /sys/bus/thunderbolt/devices/domain0/security

A value of 1 for iommu_dma_protection indicates that your system provides DMA protection via IOMMU, enhancing security against potential DMA attacks.

Method 3: Authorizing USB4 Devices for PCIe Tunneling

USB4 and Thunderbolt allow devices to establish PCIe tunnels. However, for security purposes, these tunnels are not automatically enabled. You must manually authorize devices to use PCIe tunneling.

Step 1: Plug in your USB4 device and identify it using the following command:

ls /sys/bus/thunderbolt/devices/

The device will appear as a directory, such as 0-1. Check its authorization status:

cat /sys/bus/thunderbolt/devices/0-1/authorized

A value of 0 indicates the device is not yet authorized.

Step 2: To authorize the device for PCIe tunneling, write 1 to the authorization file:

echo 1 | sudo tee /sys/bus/thunderbolt/devices/0-1/authorized

After this command, the PCIe tunnels will be established, and the device will become fully operational.

Caution: Authorizing devices bypasses some security measures. Always ensure you trust the device before authorizing it.

Method 4: Automatically Authorizing USB4 Devices (Advanced Users)

If you trust all USB4 and Thunderbolt devices you connect, you can automate authorization. Create a udev rule by editing the file /etc/udev/rules.d/99-local.rules and adding this line:

ACTION=="add", SUBSYSTEM=="thunderbolt", ATTR{authorized}=="0", ATTR{authorized}="1"

This rule automatically authorizes any newly connected USB4 or Thunderbolt device. Remember, this approach increases vulnerability to DMA attacks, so use it with caution and only in trusted environments.

Method 5: Upgrading NVM Firmware for USB4 and Thunderbolt Controllers

Firmware updates ensure your USB4 and Thunderbolt hardware operates reliably and securely. Manufacturers typically offer firmware updates through their support websites.

Step 1: Download the latest NVM firmware image from your hardware vendor's support page. Ensure the firmware matches your exact hardware model.

Step 2: Identify your Thunderbolt controller in the sysfs interface and write the firmware image to the non-active NVM partition:

sudo dd if=firmware.bin of=/sys/bus/thunderbolt/devices/0-0/nvm_non_active0/nvmem

Step 3: Trigger the firmware upgrade process by authenticating the new firmware.

echo 1 | sudo tee /sys/bus/thunderbolt/devices/0-0/nvm_authenticate

Your Thunderbolt controller will reset, and after a brief pause, the new firmware will become active. Verify that the upgrade was successful by checking the firmware version:

cat /sys/bus/thunderbolt/devices/0-0/nvm_version

Make sure the version matches the firmware you installed.

USB4 support in Linux Kernel 6.5 significantly improves connectivity options, ensuring faster data transfers and better hardware compatibility. By following these methods, you can confidently verify and enable USB4 on your Linux system, taking full advantage of this powerful technology.