Thunderbolt Is Seeing A Lot Of Improvements For Linux 5.2

Adding to the excitement of the Linux 5.2 kernel changes are a lot of Thunderbolt improvements expected to be introduced in this next kernel cycle.

Mika Westerberg of Intel has been working on a lot of Thunderbolt connectivity improvements destined for Linux 5.2 and in recent days has begun staging this work in the thunderbolt-next tree ahead of the Linux 5.2 kernel merge window opening in May.

This work includes support for full PCIe daisy chaining within the Thunderbolt software connection manager:

Currently the software connection manager (tb.c) has only supported creating a single PCIe tunnel, no PCIe device daisy chaining has been supported so far. This updates the software connection manager so that it now can create PCIe tunnels for full chain of six devices.

And there's also the support for DisplayPort tunnels:

Display Port tunnels are somewhat more complex than PCIe tunnels as it requires 3 tunnels (AUX Rx/Tx and Video). In addition we are not supposed to create the tunnels immediately when a DP OUT is enumerated. Instead we need to wait until we get hotplug event to that adapter port or check if the port has HPD set before tunnels can be established. This adds Display Port tunneling support to the software connection manager.

Along with DMA tunnels:

In addition to PCIe and Display Port tunnels it is also possible to create tunnels that forward DMA traffic from the host interface adapter (NHI) to a NULL port that is connected to another domain through a Thunderbolt cable. These tunnels can be used to carry software messages such as networking packets.

Those are among the changes currently in the "next" branch for Thunderbolt of new material set to come with the Linux 5.2 kernel this summer.