Re: [Qemu-devel] [PATCH] hw/pci: completed master-abort emulation

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Tue, 2013-09-24 at 19:55 +0900, Peter Maydell wrote:
> On 24 September 2013 19:44, Marcel Apfelbaum <marcel.a@redhat.com> wrote:
> > We need to check all the bridges on each bus encountered
> > for their address range; if it corresponds to the transaction address,
> > we pass the bridge to the other bus(depending on transaction's direction).
> 
> I haven't looked at all at the details, but you can probably rephrase
> this kind of "check address against range and pass recursively
> to other bridge" algorithm in terms of appropriate statically
> constructed memory regions. Since "transaction aborted" is
> definitely not a fast path, the only argument for doing it that way
> would be if the code worked out more neatly -- maybe worth
> thinking about whether it would do so?
I didn't fully understand your comment, please let me explain:

A PCI Device issues a transaction to an unassigned address,
which is in a range corresponding to a bridge on some "upper"
(close to CPU) bus.

The region that will "catch" this access is a background region
"behind" the "target" memory region (bus_master_enable_region).

At this point we know:
1. The PCI device that initiated the transaction
2. The transaction's address 

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.

Marcel

> 
> -- PMM