给你看看老外写的如何驱动A卡的原话吧。
Apple doesn’t offer framebuffers for GCN 1.1+ cards that match any available PCIe card.
苹果没有给高于GCN1.1架构的显卡提供frame buffer。(R9 390貌似属于GCN1.2吧)
Having the device ID of a specific card in both files is necessary but not sufficient to make it work! Apple will add some device IDs every now and then, and while some of the added cards will actually work, others might have awfully buggy drivers because Apple added the IDs just for testing purpose. Do not buy a card assuming it’s fully compatible just because you see the device ID in there!!
系统中有显卡ID是必要条件但不是充分条件。苹果会不时的向系统中加入某些显卡ID,有些确实能工作,但另外一些却有充满糟糕bug的驱动,因为苹果加它们仅仅用作测试。不要因为系统中有某个显卡的ID就假设它能正常工作并且购买。