linux DMA capabilities in MV64460

[KokHow Teh]

>Currently there is a 2M aperture on the device, but it is not being seen
>as "prefetchable", so when I try to get data from the device using
>repetitive reads, they are very slow.  Hence my efforts to get DMA
>happening.

>Presumably the CPU/bridge discovers PCI device memory regions during bus
>enumeration.  What characteristic of a device determines whether the
>memory region is going to be marked as "prefetchable"?

Being "prefetchable" or not is determined by bit-3 of PCI Memory BAR.

>Does this attribute also affect whether DMA will work?


  MAG> You may want to pick up "PCI System Architecture" from Mindshare,
  MAG> Inc.  There are ones for PCI-X and PCI-Express too, I think.
  MAG> Well worth the money.

>Sounds like a good idea.  I'd hoped not to have to become a PCI expert,
>but it seems that there is a lot for me to learn just to determine how
>best to design my driver.

Here is a good online reference but it does not cover dma and
cache-coherency in great details.
http://www.tldp.org/LDP/tlk/dd/pci.html