Hi, dma_map_xxx / dma_unmap_xxx pair are used to do cache coherency. see Documentation/DMA-API.txt.
dma_map_xxx: "Maps a piece of processor virtual memory so it can be accessed by the device and returns the physical handle of the memory." dma_unmap_xxx: "Unmaps the region previously mapped. All the parameters passed in must be identical to those passed in (and returned) by the mapping API." Assuming you are doing DMA_TO_DEVICE synchronization: cpu accesses buffer dma_map_xxx (after this point, cpu cannot touch the buffer) device accesses buffer device accesses buffer dma_unmap_xxx (after this point, device cannot touch the buffer) cpu accesses buffer Regards, MH On Sat, Feb 8, 2014 at 4:16 PM, m silverstri <michael.j.silvers...@gmail.com > wrote: > Hi, > > I create DMA buffer in my kernel driver. > I would like to know what is cache coherency guidelines for DMA > buffer referred by this post? > > http://stackoverflow.com/questions/5564326/linux-kernel-device-driver-to-dma-into-kernel-space > > Both my kernel driver and HW writes to the DMA buffer. I wnat to know > how to make sure cache coherency. > > Thank you. > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >
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