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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