dired-find-subdir

dired-find-subdir is a variable defined in `dired-x.el'.
Its value is

nil

Documentation:
If non-nil, Dired always finds a directory in a buffer of its own.
If nil, Dired finds the directory as a subdirectory in some other buffer
if it is present as one.

If there are several Dired buffers for a directory, the most recently
used is chosen.

Dired avoids switching to the current buffer, so that if you have
a normal and a wildcard buffer for the same directory, C-x d will
toggle between those two.

You can customize this variable.