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Re: [Qemu-devel] [PATCH v4 for-2.3 13/25] hw/acpi: remove from root bus

From: Kevin O'Connor
Subject: Re: [Qemu-devel] [PATCH v4 for-2.3 13/25] hw/acpi: remove from root bus 0 the crs resources used by other busses.
Date: Sun, 8 Mar 2015 14:46:28 -0400
User-agent: Mutt/1.5.23 (2014-03-12)

On Sun, Mar 08, 2015 at 07:34:34PM +0100, Michael S. Tsirkin wrote:
> On Sun, Mar 08, 2015 at 12:13:40PM -0400, Kevin O'Connor wrote:
> > If I read this correctly, it looks like a machine with two root buses
> > and 20 devices, each with one memory range and one io range, would end
> > up with 40 CRS ranges (ie, a CRS range for every resource).
> I think that's only if you stick multiple devices directly behind the
> bridge.  Looks like with a single pci bridge behind root, there will
> only be 2 ranges.

Yeah, that makes sense, so doesn't seem to be a problem.

> Maybe try to enforce this sane topology?
> > It also
> > looks like this furthers the requirement that the guest firmware
> > assign the PCI resources prior to QEMU being able to generate the ACPI
> > tables.
> That seems unavoidable unless we want to assign ranges from
> hardware/management.
> Which I think would be a mistake: management doesn't really know,
> or care.

I understand.  I think what would help me is if we could document
somewhere that the firmware has to assign PCI resources before
querying the bios tables and that it is the *only* pre-requisite for
querying them.  Looking now, though, I don't see any fw_cfg
documentation in the repo, so I'm not sure where that could be added.


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