They can also prefer one role, with a mechanism called Try.SNK and Try.SRC (‘try sink’ / ‘try source’).

Basically DRPs toggle back and forth between sink and source until they happen to match up (one side has switched to source and one to sink). If it doesn’t prefer to do the role it’s resolved to randomly, it can switch to the other way and wait a bit - if the other side is fine with it then it will switch too and everyone is happy, if not you can switch back.

We use this for a device that can on-charge a device when it has external power plugged in (in which case we prefer source role) but not when running on battery (in which case we prefer sink but don’t actually pull any power because it’s self powered).