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Date: Tue, 24 Sep 2013 19:24:52 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] hw/pci: completed master-abort emulation
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Anthony Liguori <anthony@codemonkey.ws>, Marcel Apfelbaum <marcel.a@redhat.com>

On Tue, Sep 24, 2013 at 06:41:11PM +0300, Michael S. Tsirkin wrote:
> On Tue, Sep 24, 2013 at 08:21:50PM +0900, Peter Maydell wrote:
> > On 24 September 2013 20:17, Marcel Apfelbaum <marcel.a@redhat.com> wrote:
> > > I was suggesting an algorithm to find the MA device in order
> > > to set MA Received Bit in its Status(Sec_Status) register.
> > >
> > > The algorithm was to traverse the PCI buses for finding the
> > > MA device using the transaction address.
> > 
> > Yes. My point is that if you have an algorithm phrased as
> > "dynamically traverse some hierarchy using an address
> > to find something" then you can rephrase it as "statically
> > construct a hierarchy of memory regions and then just
> > query it with the address".
> > 
> > -- PMM
> 
> Right. You might be able to use MR hierarchy to find the last bridge to
> claim transaction.  That should to be enough for PCI, for express you
> then need to find all devices on the path between bus master and the
> last bridge.  For this task, memory subsystem can't be used I think.

Specifically, I think we need at least two things:
- initiator of the transaction
- last bridge to claim transaction

any idea how to find both at the same time?

> Whether the result will be cleaner than open-coding it all, I don't
> really know.
> 
> -- 
> MST