Geiser binds M-p to `comint-previous-matching-input-from-input' in the REPL. Usually, M-p is bind to `comint-previous-input' in comint-mode and `comint-previous-matching-input-from-input' is bind to C-c M-r.
This is a personal preference, but I usually hit M-p pretty often and the current Geiser behavior leaves the cursor at the beginning of the input, so I have to hit some keys to move it to the end of the input so I can re-evaluate a previous expression. IMO M-p bind to `comint-previous-input' is better, given my usage of it.
