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_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)
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.silverstri@xxxxxxxxx> 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.
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