Assume the poem is about a loving father son relationship. What role would the author's tone and diction play in determining this?"My Papa's...

Most often, this poem is looked at as an example of harsh
discipline at best, and mild abuse at worse.  To take the lighter side and assume that
the relationship between the father and son is indeed loving, there are only a couple of
clues from the text, which much be greatly
stretched.

Diction means word choice. 
The title of the poem is called "My Papa's Waltz."  A waltz
is a lighthearted dance, and the poem suggests the dance is between him and his father. 
Ignoring the possibility of purposeful irony here, the fact that the son considers his
relationship with his father like a dance, could imply a loving
relationship.  Also, he talks about the whiskey on his father's breath that could make a
"small boy dizzy."  Young children actually enjoy spinning around and becoming dizzy. 
When looked at in isolation, the strength of the smell of whiskey causing potential
dizziness and the fact that the boy "hung on like death" could be a positive
thing.

Also, the use of the word
romped suggests playful
wrestling.

The final line of the poem also presents some
diction which could suggest a loving relationship.

readability="5">

Then waltzed me off
to bed
Still clinging to your
shirt

Being "waltzed off to
bed" is actually a somewhat common figure of speech which is often presented in a loving
manner.  The boy is still "clinging" to his fathers shirt.  If it was really abuse,
would he not try to run and hide?

The entire tone of this
poem comes across as lighthearted and dance like.  The rhythm of the poem mimics the
rhythm of a waltz.  I do not, however, believe this is meant to mean that the
relationship between the father and son in loving.  Instead, I think it is done to give
the false pretense of a loving relationship with a hidden dark
side.  The boy tells the story, after all, and what child is able to understand, let
alone admit, that his father is an abusive drunk?  If the speaker is looking back on
this time from an adult perspective, he is most successful in showing the reality for
what it was, but presenting how his childhood-self interpreted it at the
time.