Question: pick up by the sum of the list elements

Say I have this list,

tmp:=[[0, 1, 2], [1, 0, 2], [1, 1, 2], [1, 2, 0]];

and the sums of each element (list),

map(x->convert(x,`+`),tmp);

 

How do I quickly pickup the elements, where they sum to 3? Like this:

wanttohave:=[[0, 1, 2], [1, 0, 2],  [1, 2, 0]];

Thanks,

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