Question on DMA mask

Hi everyone,

I am working on a SOC which it's RAM starts at 0x200M.
For some reason I need to limit the DMA allocations up to 0x220M, so I called  - dma_set_mask_and_coherent(mmc_dev(mmc), 0x21FFFFFFF).
I noticed that dev->dma_mask  was not set, while dev->coherent_dma_mask was set.
Still, calling dma_alloc_coherent returns buffers above the requested limit.
How can I limit the buffer address?