cache coherency guidelines for DMA buffer

[Miles MH Chen]

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.silverstri at 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 at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20140208/5de92be7/attachment-0001.html