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

Leon Woestenberg
2009-06-17T01:13:17Z

Hello Benjamin,

On Wed, Jun 17, 2009 at 3:08 AM, Benjamin
Herrenschmidt<benh@kernel.crashing.org> wrote:
> 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.
>
Thanks, then at least I understand things in the corr^H^H^H^Hsame way :-)

And btw, I hadn't seen any data mismatch yet.

Regards,
--
Leon 'likewise' Woestenberg