Crossword Genius

If upset and cross, all you need is some dope! (3)

Ross

I believe the answer is:

fix

I'm a little stuck... Click here to teach me more about this clue!

'all you need is some dope' is the definition.
I can't judge whether this defines the answer.

'if upset and cross' is the wordplay.
'upset' says the letters should be written in reverse.
'and' is a charade indicator (letters next to each other).
'cross' becomes 'x' (X is cross-shaped).
'if' back-to-front is 'fi'.
'fi'+'x'='FIX'

Can you help me to learn more?

(Other definitions for fix that I've seen before include "Addict's dose of drug" , "mess" , "Repair or attach" , "Mend" , "Fasten" .)

I've seen this clue in the Evening Standard.
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