cache coherency guidelines for DMA buffer

[m silverstri]

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.