I mainly think of PD ports in reference to charging, not data. I know dock PD ports do both, so I know data+PD is possible, but can my laptop's USB-C port support PD in both directions (charging and powering a peripheral)?. That's my main question -- most of my exposure to PD is with charging only... not powering peripherals. I know I can charge my phone with my laptop, but I've never looked to see how fast it is charging.

And more importantly, what do available chips support? How easy is it to get chips that support PD + data?

This isn't my area of expertise, so I was hoping someone would be able to say -- Yes, it's possible, I do this all the time. Or -- it's theoretically possible, but not widely supported, so no one does it.

> but can my laptop's USB-C port support PD in both directions (charging and powering a peripheral)?.

Two of the USB-C ports of my Dell XPS 13 9380 provide 5A/3A over PD, and the third one provides 5A/1.5A. All of them can negotiate both sink and source PD contracts.

If your laptop can be charged via USB-C port and you can attach peripherals to the same port, it's almost certain that it can negotiate a source PD contract as well. That doesn't automatically mean you'll get more than 5V though, so such PD port may still be useless for powering a disk drive enclosure without additional voltage regulation.

I'm assuming you mean 5V/3A and 5V/1.5A. If so, that is explicitly NOT PD. USB-C supports 3A and 1.5A purely by setting resistor values on the CC pins, and does not require the BMC PD negotiation protocol.

Many PD controllers support this for 'sourcing' (5V/1.5A or 5V/3A) natively, since it's a common use case for laptops.

No, this is 5V/3A and 5V/1.5A as communicated via PD 3.0. In this case you can achieve the same result without PD (well, almost - you still need it for role swap), but that's not what I was talking about.

What scenario would your laptop be providing power (being the source), while simultaneously being the receiver of data (data sink)? Not sure I see the use case for that, regardless of whether you can achieve 5V/3A over PD.

You need PD for power role swap. You also need PD for alt-mode negotiation. You can get a 5V/3A contract to power a USB-C hub with DisplayPort, for example - that won't work with simply signaling 3A with a resistor.

Understood you need PD for alt modes, that's a given. I never thought about the scenario where you have a powered USB hub and you switch from powering it via a brick to powering it via your laptop... interesting, and actually very reasonable scenario. I guess given you have PD already built-in, it's not too hard to integrate that functionality either.