Troy Maxson is actually quite patient and even gentle with his brother, Gabriel, at least compared to how he responds to the rest of the family at times. Troy knows, of course, that Gabriel's war injury has caused irreversible brain damage. Gabriel cannot help the way he is, and Troy does his best to treat him kindly.
When Gabriel first appears in the play, he is worried that Troy is mad at him for getting his own place. Falling back on a slightly gruff manner, Troy assures his brother, “I ain't mad at you. What I got to be mad at you about? You ain't done nothing to me.” He then tells Gabriel that it's good that he has his very own key (because Gabriel is quite happy about it). Gabriel, as he apparently has many times before, assures Troy that the latter's name is written in St. Peter's book. Troy, with just a tinge of impatience (he really does have to struggle sometimes), asks Gabriel how many times he is going to tell him that. But then he listens to his brother's story before telling him to go into the house to eat. When Gabriel wanders off, Troy merely lets him go.
Later in the play, Gabriel again wonders if Troy is mad at him. Once again, Troy tells him, “Naw, Gabe, I ain't mad at you.” Troy remains patient with Gabriel even though his brother interrupts an argument between Troy and Rose about Troy's infidelity. That definitely tells us something about Troy's commitment to, and even love for, his brother.