Grangegorman (St Brendan's) Richmond Lunatic Hospital

Looking to find information on a patient, my grandfather, Peter Cahill, who entered this hospital, post 1930.
He was in the British Navy during WWI 1914 - 1919. It is said that he had suffered (shell shock) which is now probably termed as PTSD, neurasthenia.
I'd be interested in any information regarding Grangegorman Hospital, also St. Mary's Hospital in the grounds of Phoenix Park, in regards to accessing records, timeline, or anything pertinent to its history etc.
Many thanks in anticipation.