Thunderbolt Networking Support For Linux Still Being Worked On

[arbition]

Thunderbolt *is* PCIe (+ displayport).
Besides, the way the news is written makes you think that thunderbolt networking currently does not work under linux but I've got a thunderbolt port since 3 years on my macbook pro which always worked just fine with a thunderbolt <-> ethernet adapter (which is basically an external PCIe network card).

The way I interpreted it was that this was about direct DMA access over thunderbolt being used for networking. I didn't have the perception that it affected all networking over thunderbolt. It might be the case that I know enough about it to be able to work that out fairly quickly, so perhaps it could be perceived that way... I'm just thinking of the old DMA security problems that started with firewire.

[torsionbar28]

I'm just thinking of the old DMA security problems that started with firewire.

DMA "security problems" lol. Firewire was not the first external interface with DMA access....

[arbition]

Fair point, certainly seemed like the start of awareness though. Maybe that is just related to my exposure to it.

[starshipeleven]

DMA "security problems" lol. Firewire was not the first external interface with DMA access....

But security became a problem later.

[westeri]

I wasn't as lucky. I got a work laptop (Fifth gen Lenovo thinkpad x1 carbon) and a compatible Lenovo thunderbolt 3 dock, and pretty much expected everything to work under Linux. Well, the only thing that actually works on the dock are the displayports and HDMI. No USB, no Ethernet. Tried with newest kernel versions as well. No luck.

It is expected to work like that. Thunderbolt security level is typically set from BIOS to "User approval" which means that the Thunderbolt controller only creates tunnels for non-PCIe devices (to prevent DMA attacks). With the recent kernels v4.13+, all devices appear under /sys/bus/thunderbolt/devices/* and can authorize them by writing "1" to DEVICE/authorized file. It is all explained here:

https://www.kernel.org/doc/html/latest/admin-guide/thunderbolt.html

While you can do that manually, it is pretty awkward so it requires some userspace tooling as well. There is a work in progress here:

https://github.com/01org/thunderbolt-software-user-space

which then allows you to "authorize" devices permanently among other things.

Since this is pretty recent addition to the kernel distros are still catching up, so it may take some time until all necessary tooling is in place.

One more thing if you are running v4.13. There is a bug how Linux handles ACPI GPEs that basically prevent you from booting the system with Thunderbolt device connected. This is fixed in v4.14-rc1 and we are planning to back port it to v4.13 once it gets some more testing. The patch series is here:

https://lkml.org/lkml/2017/8/9/1017

So for v4.13 it is better to connect Thunderbolt device after the system has been booted up.

[Guest]

Thunderbolt 3 and DP are both alternate modes for USB-C. There isn't a DP alternate mode for Thunderbolt 3 as such, however thunderbolt 3 ports (almost?) always support DP too.

If they are independent alternate modes for USB-C, then this is in contradiction with following comment:

Thunderbolt in its currentl revision is limited to DisplayPort 1.2, while there is no such limit for DisplayPort alternate mode.

So, thunderbolt revision/documentation wouldn't state a DisplayPort 1.2 support, but support for DisplayPort Alternate Mode over USB-C. So, how is it really?

[patstew]

If they are independent alternate modes for USB-C, then this is in contradiction with following comment:



So, thunderbolt revision/documentation wouldn't state a DisplayPort 1.2 support, but support for DisplayPort Alternate Mode over USB-C. So, how is it really?

I was mistaken actually. It's true that Thunderbolt 3 and DP are both alternate modes for USB-C, and Thunderbolt 3 hosts support the ordinary DP alternate mode. However the ordinary DP alternate mode is multiplexed at the level of switching pairs in the cable, you can either have one USB3 pair and one DP pair or 2 DP pairs (for higher bandwidth/resolution). Thunderbolt 3 multiplexes DP/USB/PCIe at the packet level when you have a thunderbolt 3 device, which wastes less bandwidth in addition to being faster.

So any USB-C host that has video out e.g. intel based laptops, many modern smartphones should work with a cheap USB-C to DP adapter. Thunderbolt 3 hosts will, in addition, work with thunderbolt 3 devices. The only thing that won't work is plugging a thunderbolt 3 device like the Dell TB16 dock into an ordinary USB host.
I think the main case where it wouldn't work at all would be using a USB-C/Thunderbolt 3 motherboard with a CPU that doesn't have an integrated GPU.

[chithanh]

What also won't work with Thunderbolt ports is plugging in a non-Thunderbolt 4K monitor with USB Type-C connector and running 4K@60 Hz while also using USB 3.

While the same works fine with DisplayPort alternate mode since 1.3, and also some DP 1.2 devices which additionally support DSC (like recent Exynos and Snapdragon SoCs).

[boltronics]

Article title was misleading. I though this was talking about Ethernet dongles, which surprised me because mine works perfectly with Thunderbolt. I don't think Thunderbolt -> Thunderbolt networking is all that useful - although it should be nice and fast at least!

[torsionbar28]

I don't think Thunderbolt -> Thunderbolt networking is all that useful - although it should be nice and fast at least!

It should have significantly lower latency as compared with Ethernet. Latency sucks on Ethernet, at least in HPC applications. It's why the big supercomputers don't use it as their interconnect - they use specialized low latency interconnects instead. Back when I was building DEC Alpha supercomputers in the early 2000's, the leaders were Myrinet, Dolphin, and Quadrics. Gig-E was available too, but the latency was so terrible, nobody used it outside of the low-budget "Beowulf" builds in University student labs. I think Infiniband had a brief foray into supercomputer interconnects, but nowadays I think it's all proprietary stuff like Cray Gemini, Aries, and SeaStar2+. Anyhow, I'd be curious about how Thunderbolt's network latency compares.