The general rule for street photography in the US (to the best of my knowledge) is pictures taken in public areas, where there is no expectation of privacy, require no releases if not used commercially or editorially. But every municipality has some variation of where, when and what may be photographed. Again mostly this addresses commercial photo shoots. No trespassing, no invasion of privacy, such as shooting into someone's window, no creating obstructions or dangerous situations, no picture taking where signs prohibit picture taking, and being careful around official buildings and sites would all be worth remembering. Also, if someone is complaining about pictures being taken, I walk away. I do not know Portland, but I would think the above advice would suffice there as well.