showing the dharma of permanance of the buddha nature.
This is not right.
Buddha nature is not permanent. If Buddha nature is permanent, that is atman.
We should know that Buddha nature is just a name for the sake of communication referring to the baseless and rootless.
And in that, the word permanent and impermanent are not valid.
We need to be careful when we discuss Buddha nature because permanent lead to atman. Impermanence lead to changing, which again changing implies something unexplainable must be changing.
When we discuss Buddha nature, we need to make sure the language that we use doesn't give rise to these 2 extremes.
Permanent is extreme.
Impermanent is opposite of permanent. Which is also extreme.
And Buddha nature is none of them.