DMA controller on Northbridge?

[Kostik Belousov]

On Tue, Mar 22, 2011 at 10:11:04AM -0700, 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.

I believe what are you looking for is
ftp://download.intel.com/technology/.../Intel(r)_VT_for_Direct_IO.pdf

On my X58 machine it is shown like this:
none6 at pci0:0:22:2:   class=0x088000 card=0xf38015d9 chip=0x34328086 rev=0x12 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'DMA Engine'
    class      = base peripheral
    cap 11[80] = MSI-X supports 1 message in map 0x10
    cap 10[90] = PCI-Express 2 root endpoint max data 128(128) link x0(x0)
    cap 01[e0] = powerspec 3  supports D0 D3  current D0


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