dired-auto-revert-buffer is a variable defined in `dired.el'.
Its value is

Automatically revert Dired buffer on revisiting.
If t, revisiting an existing Dired buffer automatically reverts it.
If its value is a function, call this function with the directory
name as single argument and revert the buffer if it returns non-nil.
Otherwise, a message offering to revert the changed dired buffer
is displayed.
Note that this is not the same as `auto-revert-mode' that
periodically reverts at specified time intervals.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.