Re: bus-dma question

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 09/26/05

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    To: freebsd-hackers@freebsd.org, hselasky@c2i.net
Date: Mon, 26 Sep 2005 15:25:05 -0400

    On Monday 26 September 2005 01:31 pm, Hans Petter Selasky wrote:
    > Hi,
    >
    > I see something suspicious on Amd64, when allocating small blocks of
    > DMA-able memory:
    >
    > bus_dmamap_load_callback: 0x0000000000caf200
    > ^^^^ this is physical address
    >
    > QH(0xffffff0000caf200) at 0x00caf200:
    > ^^^^ this is kernel address
    >
    > Shouldn't kernel addresses always be different from physical addresses ?

    No. Especially not on archs like alpha, ia64, amd64, and sparc64 where part
    of KVA is direct-mapped to physical memory either in hardware (alpha's K0Seg)
    or via software (ia64, amd64, and sparc64).

    > When allocating larger blocks of memory I get, for example:
    >
    > bus_dmamap_load_callback: 0x000000003bc50000
    >
    > which seems correct.
    >
    > --HPS
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    -- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org
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