Halliday & Matthiessen (2014: 568):
The secondary group may be perfective, with or without to, e.g. (to) do; or imperfective, e.g. doing, in aspect. The other non-finite form, the ‘past/passive participle’, e.g. done, usually stands for the perfective, as in I want it (to be) done, consider it (to have been) done; but in itself it is neutral, and in other contexts it neutralises the distinction, e.g. I saw it (be/being) done.