BBB enable UART DMA 3.8 kernel?

Sorry if this is a dumb question, but how do I configure the AM335x’s UARTs to use DMA mode under the 3.8 version of the kernel? Is it already configured to use DMA?

After Googling, the closest I can find is someone saying “use platform_data to enable DMA,” but I’m sort of new to kernel hacking so I’m not sure how I would do that.