Re: PowerPC PCI DMA issues (prefetch/coherency?)

From: Benjamin Herrenschmidt
Date: Tue Jun 16 2009 - 21:11:07 EST

On Wed, 2009-06-17 at 02:56 +0200, Leon Woestenberg wrote:
> I use pci_map_sg(), have the device perform either DMA master reads or
> writes to the bus address using PCIe.
> After that, I use pci_unmap_sg().
> My assumption is that pci_unmap_sg() either makes the cache coherent
> or invalidated and thus I do not need to take further actions.
> This is on a MPC83xx or 85xx system.
> Is this assumption correct?

It is, as far as I understand things :-) Those APIs are fun.

You should only need the explicit sync calls if you are going to peek or
poke at the DMA mapped memory before you unmap it.


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