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

Liviu Dudau
2014-11-18T14:24:06Z

On Tue, Nov 18, 2014 at 11:46:06AM +0000, Yijing Wang wrote:
> On 2014/11/18 17:36, Arnd Bergmann wrote:
> > 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.
>
> Ok, I will move this out of the generic interface.

My suggestion would actually be to trigger a warning/error if you detect that the resources
are missing. That way we can force the drivers to clean up.

Best regards,
Liviu

>
> Thanks!
> Yijing.
>
> >
> > Arnd
> >
> > .
> >
>
>
> --
> Thanks!
> Yijing
>
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