  The thermodynamics for regular black holes (RBHs) is considered under the
restricted phase space (RPS) formalism. It is shown that the RPS formalism
seems to hold for RBHs, however, in order for the extensive thermodynamic
parameters to be independent from each other, the RBHs need to be viewed as
intermediate thermodynamic states in a larger class of black holes (BHs) which
admit both regular and singular states. This idea is checked for several
classes of BHs. In particular, for the electrically charged Hayward class BHs,
it is shown that the regular states can either be thermodynamically stable or
unstable, depending on the amount of charges carried by the BHs. The
quasinormal frequencies for the Hayward class BHs are also analyzed, and it
turns out that, even for the thermodynamically unstable regular states, the
dynamic stability still holds, at least under massless scalar perturbations.
