Re: [RFC/RFT PATCH 03/18] PCI: Introduce pci_scan_root_bus_bridge()

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Apr 28, 2017 at 02:28:38PM +0200, Arnd Bergmann wrote:
> On Wed, Apr 26, 2017 at 1:17 PM, Lorenzo Pieralisi
> <lorenzo.pieralisi@arm.com> wrote:
> > Current pci_scan_root_bus() interface is made up of two main
> > code paths:
> >
> > - pci_create_root_bus()
> > - pci_scan_child_bus()
> >
> > pci_create_root_bus() is a wrapper function that allows to create
> > a struct pci_host_bridge structure, initialize it with the passed
> > parameters and register it with the kernel.
> >
> > As the struct pci_host_bridge require additional struct members,
> > pci_create_root_bus() parameters list has grown in time, making
> > it unwieldy to add further parameters to it in case the struct
> > pci_host_bridge gains more members fields to augment its functionality.
> >
> > Since PCI core code provides functions to allocate struct
> > pci_host_bridge, instead of forcing the pci_create_root_bus() interface
> > to add new parameters to cater for new struct pci_host_bridge
> > functionality, it is more suitable to add an interface in PCI
> > core code to scan a PCI bus straight from a struct pci_host_bridge
> > created and customized by each specific PCI host controller driver.
> >
> > Add a pci_scan_root_bus_bridge() function to allow PCI host controller
> > drivers to create and initialize struct pci_host_bridge and scan
> > the resulting bus.
> >
> > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> 
> Good idea, yes. To avoid growing the number of interfaces too
> much, should we change the existing users of pci_register_host_bridge
> in host drivers over to this entry point, and make the other one
> local to probe.c then?

Yes, the problem is that there are drivers (ie pcie-iproc.c) that
require the struct pci_bus (created by pci_register_host_bridge())
to fiddle with it to check link status and THEN scan the bus (so
the pci_register_host_bridge() call can't be embedded in the scan
interface - the driver requires struct pci_bus for pci_ops to work
before scanning the bus itself).

I will see how I can accommodate this change because you definitely
have a point.

> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 7e4ffc4..c7a7f72 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -2412,6 +2412,44 @@ void pci_bus_release_busn_res(struct pci_bus *b)
> >                         res, ret ? "can not be" : "is");
> >  }
> >
> > +int pci_scan_root_bus_bridge(struct pci_host_bridge *bridge)
> > +{
> > +       struct resource_entry *window;
> > +       bool found = false;
> > +       struct pci_bus *b;
> > +       int max, bus, ret;
> > +
> > +       if (!bridge)
> > +               return -EINVAL;
> > +
> > +       resource_list_for_each_entry(window, &bridge->windows)
> > +               if (window->res->flags & IORESOURCE_BUS) {
> > +                       found = true;
> > +                       break;
> > +               }
> > +
> > +       ret = pci_register_host_bridge(bridge);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       b = bridge->bus;
> > +       bus = bridge->busnr;
> > +
> > +       if (!found) {
> > +               dev_info(&b->dev,
> > +                "No busn resource found for root bus, will use [bus %02x-ff]\n",
> > +                       bus);
> > +               pci_bus_insert_busn_res(b, bus, 255);
> > +       }
> > +
> > +       max = pci_scan_child_bus(b);
> > +
> > +       if (!found)
> > +               pci_bus_update_busn_res_end(b, max);
> > +
> > +       return 0;
> > +}
> > +
> 
> We probably want an EXPORT_SYMBOL() here as well.

Yep, sure.

Thanks for having a look !

Lorenzo

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