On Thu, May 25, 2017 at 03:56:43PM -0500, Bjorn Helgaas wrote:
> [+cc Ray, Scott, Jon]
>
> On Tue, May 02, 2017 at 06:15:01PM +0100, Lorenzo Pieralisi wrote:
> > 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@xxxxxxx> 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@xxxxxxx>
> > > > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > >
> > > 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 think code like iproc_pcie_check_link() that requires a struct
> pci_bus before we even scan the bus is lame. I think the driver
> should be able to bring up the link before telling the PCI core about
> the bridge. Aardvark uses a typical pattern:
>
> advk_pcie_probe
> advk_pcie_setup_hw
> advk_pcie_wait_for_link
> pci_scan_root_bus
>
> I would rather see iproc restructured along that line than add a
> callback.
>
> That would require replacing the pci_bus_read_config uses in
> iproc_pcie_check_link() with something different, maybe iproc-internal
> accessors. Slightly messy, but I think doable.
I agree with you, it probably requires some cfg space accessors copy
and paste though but that's doable. I can write the patch myself but
I can't test it so help is appreciated here.
Thanks,
Lorenzo
> > 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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