Re: [RFC PATCH 01/16] PCI: Enhance pci_scan_root_bus() to support default IO/MEM resources

Arnd Bergmann
2014-11-18T09:38:10Z

On Tuesday 18 November 2014 15:44:23 Yijing Wang wrote:
> On 2014/11/17 18:08, Arnd Bergmann wrote:
> > On Monday 17 November 2014 18:21:35 Yijing Wang wrote:
> >> - list_for_each_entry(window, resources, list)
> >> - if (window->res->flags & IORESOURCE_BUS) {
> >> - found = true;
> >> - break;
> >> - }
> >> + if (!resources) {
> >> + pci_add_resource(&default_res, &ioport_resource);
> >> + pci_add_resource(&default_res, &iomem_resource);
> >> + pci_add_resource(&default_res, &busn_resource);
> >> + } else {
> >>
> >
> > Isn't it almost always wrong to do this? You are adding all of the
> > I/O ports and memory to the host bridge, which will prevent you from
> > adding another host bridge, and the iomem_resource normally
> > includes a lot of addresses that are not accessible by the PCI host.
>
> Hi Arnd, pci host bridge windows are the ranges allow child devices to setup
> from. Add all of IO/MEM here just a limit to child devices, no request for these
> resources, so it won't hurt another host bridge. Some platforms have no dts or ACPI
> report host bridge resources, in this case, we directly assign ioport/iomem_resources
> as the root resources of PCI devices.

But it would be wrong to allow hosts to allocate a device BAR that is not
visible through the host bridge. I think we need to keep these separate
from the general case: if you call any of the modern interfaces you have
to provide the resources and a device. I notice that there is only one
caller of pci_scan_bus_parented(), we should probably change that over to
pci_scan_root_bus() or your new interface and remove the old one, but
keep pci_scan_bus() as the only entry point for all of the legacy users
that do not know about the resources.

Arnd