Re: bus-dma question

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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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• Previous message: Hans Petter Selasky: "bus-dma question"
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