bus-dma question
John Baldwin
jhb at FreeBSD.org
Mon Sep 26 12:29:51 PDT 2005
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 at FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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