Re: [Qemu-devel] [PATCH RFC v2 2/2] hw/pci: handle unassigned pci addresses

[Peter Maydell]

On 9 September 2013 14:07, Marcel Apfelbaum <address@hidden> wrote:
> This is exactly my point. ALL device on the bus can be masters
> of a DMA transaction. So adding an interface as suggested by
> Michael: pci_set_master_for_master_abort(PCIBus *, PCIDevice *)
> for the general case (a device doing DMA) it is too far from reality.

Actually I don't think it would be too painful.
At the moment in do_pci_register_device() we do this to
create the memory region used by a device for its bus
master transactions:

    memory_region_init_alias(&pci_dev->bus_master_enable_region,
                             OBJECT(pci_dev), "bus master",
                             dma_as->root, 0,
                             memory_region_size(dma_as->root));

If instead of using this alias directly as the
bus_master_enable region you instead:
 * create a container region
 * create a 'background' region at negative priority
   (ie one per device, and you can make the 'opaque' pointer
   point to the device, not the bus)
 * put the alias and the background region into the container
 * use the container as the bus_master_enable region

then you will get in your callback a pointer to the
device which caused the abort. You can then have your
callback call a method defined on PCIDevice which we
implement:
 * as do-nothing in the PCI device base class
 * as set-the-master-abort bit in the PCI host bridge
   class
(and anybody who wants to get fancy about handling aborts
can override it in their own device implementation)

That seems achievable without really requiring new
infrastructure. Have I missed something that wouldn't
work if we did this?

thanks
-- PMM