The Constitution is pretty clear on the matter of the government and religion: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."
But what about when the believer in question is in prison, a circumstance that by its very nature involves the limitation of freedom?
Inmates from multiple alternative faiths have complained in the past that their rights were being trampled because they were not allowed access to various items. The reasons for some of the bans is obvious: knives and candles, for example, create a clear threat within a prison. And I know of no case where such items are actually required by a religion, as prisoners sometimes insist. A ceremonial knife is, indeed, a central tool to Wiccan practice, for example. That doesn't mean you can't practice without one.
But what about non-threatening items such as books? A Satanist inmate in Montana is suing because he is being denied access to central Church of Satan texts (among other complaints). I'm not an expert on the rules of reading material within prisons, but I would think that if other prisoners are allowed access to religious books, Satanic prisoners should be afforded the same options.
If there's an issue as to the content of the books, that becomes more complicated. However, if the objection is simply "because it's Satanic," then such objection is categorically unconstitutional.