Hacker News Reader

Comment by bestham | Hacker News Reader

USB-C IS DisplayPort (among other things). You can get from USB-C to DP "passively", just by signalling the right thing to the USB-C port. The mode is called Alt-Mode and gives you DisplayPort and USB2 or USB3 speeds as a side channel (depending on the amount of bandwidth consumed by the DisplayPort stream). Barring that, some USB-C docks rely on a USB data stream (DisplayLink) and not a DisplayPort stream. Avoid these.

View on HN

Yes, sometimes, often, usually, but not always! And it's really, REALLY hard to know which is which. No two host/receiver/intermediary devices (all with USB-C) can be guaranteed to support the same over-the-wire protocols, even if they all are technically USB-C. They all look the same and are separated only by some obscure icon or a few letters on the cable. And even if it actually does support the same protocols, there's STILL a good chance that your particular dock/cable/device won't support the "advanced" features like 4k/HDR/high refresh rate.

It's never plug-and-play, it's more like buy, return, buy, return, research, buy, scream, thrash, cry, and go back to HDMI/big DisplayPort in my experience.

But you can never be sure if a dock will work for your device I am below 40% succes rate. Though I do not really care much about it, luckily it worked at home on first try but it was expensive.

No, you're talking about Thunderbolt. USB-C is the shape of the port, but Displayport over USB-C is called Thunderbolt.

I have had laptops that had USB-C ports that didn't support video.

But there is DP Alternate Mode which is basically allows USB PD + Display Port + USB 2.0

One of the use cases is "almost passive" USB-C dock (typically it has USB 2.0 hub + Ethernet on it).

I don't think this is correct either. The USB C port has to support DP Alt Mode, which not all do, but it doesn't have to be a Thunderbolt port.

More than anything this probably highlights what a mess the standards are.

You are correct: https://www.cablematters.com/Blog/USB-C/what-is-dp-alt-mode

Reply on news.ycombinator.com