[spilk]

I think the main source of the confusion is that the connector is called USB-C, but devices that use the connector may not be USB devices at all, since they can fully expect to only be used with devices that support a specific alternate mode (e.g. Thunderbolt). Yes, they all have to support USB at some level to negotiate the alternate mode (i'm not sure if for USB-C this is a passive signaling like sense resistors or something active like an authentication chip), but devices don't have to fall back to USB data modes at all if they don't want to.

If they had called the connector something distinct, like for example "Omnibus", then you could additionally specify the signalling required to make it work. So you could sell a device as being "USB via Omnibus plug", or "Displayport via Omnibus plug". Maybe even come up with little icons for each mode and place them on the host computers and peripherals to help people figure out what is going to work. Really just anything more than what they've done currently would be useful.

[pyrophane]

Yea, it used to be generally true that "if you can connect them with a cable, they will be compatible." Ports were single-use, and if two ports weren't compatible, then they would be physically incompatible. If you could get a cable to connect two different ports, they would probably be compatible because who would make the cable otherwise, right?

Now we have something like your "omnibus" port in USB-C, so you have potential incompatibility at the port level and at the cable level, and no good way to tell what will work and what won't. The good news is you only have one port, but the bad news is you don't really only have one port.

[SixSigma]

> if two ports weren't compatible, then they would be physically incompatible

they have forgotten about poka-yoke (inadvertent error prevention) which is very remiss.

https://en.wikipedia.org/wiki/Poka-yoke

[gurkendoktor]

A problem that Apple used to understand, if you look at their keyboard USB cords:

http://www.mcelhearn.com/images/articles/20060828181525223_1...

I guess the USB-C plug is too small for gimmicks like this, though. Would've been nice to distinguish between USB-C and TB 3.1.

[gurkendoktor]

(For context, that is how Apple prevents people from plugging anything but its own keyboard into the extension cord, or daisy-chaining two extension cords.)

[realityking]

To be fair, that already hasn't been case with Thunderbolt 1 and 2 which reused the Mini DisplayPort.

[gurkendoktor]

True. We have a mixture of Apple's Thunderbolt and Mini-DP displays at work and it confuses the hell out of our Windows users. Some adapters/docking stations work, some don't.

[vertex-four]

There's actually a good number of very weirdly wired serial cables out there (incorrect pin mapping on one side), and if you use a standard cable your device won't work.