DMA controller on Northbridge?

Mark Tinguely marktinguely at gmail.com
Tue Mar 22 17:32:21 UTC 2011


On 3/22/2011 12:11 PM, Matthew Fleming wrote:
> How can I tell if the Northbridge on a machine has a built-in DMA
> controller?  And if it does, what device would I use to control it?
>
> I ask because I'm working with a PCI card that has a 36-bit physical
> address limit, and that means bounce buffers when using more than 64GB
> of memory.  I'd prefer not to use bounce buffers, and since the card's
> memory that I'm using is mapped into the physical space of the FreeBSD
> host, the entire address space of the card that I care about is
> available to FreeBSD.  So while pio to the card's memory is too slow
> to be useful, if there was a way to use a DMA controller on the
> motherboard to get data into and out of the card, that may be
> preferable to using the card's DMAC with the limited address space.
>
> But all that's just theory -- I have no idea how to tell whether the
> mobo has a DMAC, and if it does, how to control it.  Help? :-)
>
> Attached is the boot dmesg; I can also run pciconf commands, etc., to
> help out with figuring out what I have.
>
> Thanks,
> matthew
>
>
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Sounds like you are referring to IOMMU:

  http://software.intel.com/en-us/blogs/2009/03/02/intels-virtualization-for-directed-io-aka-iommu-part-1/

--Mark Tinguely


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