Green’s Dictionary of Slang

do you mean it? are you telling the truth?; also as a statement, truly, honestly.

1993		I. Welsh Trainspotting 10: ‘Ken wee Goagsie? He’s goat AIDS now.’ ‘Gen up?’ ah asked.
1994		I. Welsh ‘A Soft Touch’ in Acid House 51: A tenner tae you. gen up, likes.