[PATCH v3 05/12] PCI: Detect root port of internal USB4 devices by `usb4-host-interface`

[Mika Westerberg]

On Mon, Feb 14, 2022 at 09:52:02AM +0100, Lukas Wunner wrote:
> On Mon, Feb 14, 2022 at 09:34:26AM +0200, Mika Westerberg wrote:
> > On Fri, Feb 11, 2022 at 03:45:46PM -0600, Bjorn Helgaas wrote:
> > > My expectation is that "USB" (like "PCI" and "PCIe") tells me
> > > something about how a device is electrically connected and how
> > > software can operate it.  It doesn't really tell me anything about
> > > whether those electrical connections are permanent, made through an
> > > internal slot, or made through an external connector and cable.
> > 
> > It is used to identify "tunneled" ports (whether PCIe, USB 3.x or
> > DisplayPort). Tunnels are created by software (in Linux it is the
> > Thunderbolt driver) and are dynamic in nature. The USB4 links go over
> > USB Type-C cable which also is something user can plug/unplug freely.
> > 
> > I would say it is reasonable expectation that anything behind these
> > ports can be assumed as "removable".
> 
> USB gadgets may be soldered to the mainboard.  Those cannot be
> unplugged freely.  It is common practice to solder USB Ethernet
> or USB FTDI serial ports and nothing's preventing a vendor to solder
> USB4/Thunderbolt gadgets.

Right, that's why I say it is "reasonable expectation" that anything
behind these ports can be assumed "removable" :) Of course they don't
have to be but if we assume that in the driver where this actually
matters we should be on the safe side, no?