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From: John Baldwin <jhb@freebsd.org>
To: Ivan Voras <ivoras@freebsd.org>
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Cc: freebsd-hackers@freebsd.org, Sergey Babkin <babkin@verizon.net>
Subject: Re: Patch for MS Hyper V (virtualization)
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On Monday 06 April 2009 1:07:38 pm Ivan Voras wrote:
> 2009/4/6 John Baldwin <jhb@freebsd.org>:
> > On Sunday 05 April 2009 12:23:39 pm Sergey Babkin wrote:
>=20
> > Hmm, the problem is we need to be able to write to BARs to size them. =
=C2=A0Any=20
OS
> > needs to be able to do this to know what address space regions are being
> > decoded by devices. =C2=A0We can't avoid writing to BARs.
>=20
> I have only vague idea what BARs are and if it's the correct diagnosis
> in this case, but the fact is that other operating systems (Windows,
> Linux tested) work, so either there is a way around it or the original
> premise is wrong-ish.

Every OS writes to BARs to size them during boot.  It's the defined procedu=
re=20
for sizing them.  A BAR is a base address register, and it is how a PCI=20
device gets memory and I/O port resources.  OS (or BIOS) writes a starting=
=20
address into the register to tell the PCI device where a given=20
resource "starts".

=2D-=20
John Baldwin