Question about DMA mapping.

[phind.uet at gmail.com]

Hi everyone,

Thank for your time, I'm new to linux kernel. I am reading LDD3 chapter 
15, Dirrect Memory Access section. I see that when I call function 
/dma_map_single/ and /dma_unmap_single/, I need to pass a direction as a 
parameter. I wonder what is purpose of it? Does It relate to something 
like permission? Can I call /dma_map_single /with DMA_BIDIRECTIONAL and 
then call /dma_unmap_single /with DMA_TO_DEVICE? Will it cause any problem?

Thank you very much.


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