Why is Thunderbolt 3 limited to 2.5 GT/s on Linux?

[Mika Westerberg]

On Mon, Jul 01, 2019 at 10:46:34AM -0400, Alex Deucher wrote:
> > 2. As far as I understood what Mika said, there isn't really a 2.5 GT/s
> > limitation there, since the virtual link should be running at 40 Gb/s
> > regardless of the reported speed of that device. Would it be possible
> > to run the AMD GPU at 8 GT/s in this case?
> 
> If there is really a faster link here then we need some way to pass
> that information to the drivers.  We rely on the information from the
> upstream bridges and the pcie core helper functions.

I think you may use "pci_dev->is_thunderbolt" in the GPU driver and then
just use whatever the real PCI link speed & width is between the GPU and
the downstream port it connects to.