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Date: Fri, 30 Sep 2005 14:04:45 +0200 (CEST)
From: Juergen Keil <jk@tools.de>
Subject: Re: [Qemu-devel] IDE busmaster DMA support
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> I'm trying to write an IDE driver with busmaster DMA support.
> My problem is that I can't get the right controller registers addresses.
> 
> In the IDE BusMaster DMA specification :
> 
> "The control registers for the controller are allocated via the
> devices Base Address register at offset 0x20 in PCI configuration
> space."
> 
> If I read the word at offset 0x20 in the PCI configuration space, I get 
> 0xc001. But if I boot qemu with a linux live-cd, it tells me that BM-DMA 
> is at 0xc000
> 
> Do I have to init the PCI IDE controller or something ?

Bit 0 encodes if the registers are in IO (1) or in memory (0) space.
You get the IO base address by using a 0xfffffffe mask.

For memory space the mask is 0xfffffff0, the low four bits encode
a few memory properties (prefetch, 32-bit vs. 64-bit memory addresses).

See the PCI spec for more details. Or for example the PCI_BASE_* defines here:

  http://cvs.opensolaris.org/source/xref/usr/src/uts/common/sys/pci.h#519