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

[oza.oza@broadcom.com (Oza Oza)]

On Fri, May 26, 2017 at 6:37 PM, Lorenzo Pieralisi
<lorenzo.pieralisi@arm.com> wrote:
> 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@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 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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>> > linux-arm-kernel at lists.infradead.org
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>
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Hi,

This is good idea,
because the following patch of mine attempts to add inbound windows,
and I had to create another API pci_create_root_bus2

[PATCH v7 2/3] PCI: Add support for PCI inbound windows resources

Lorenzo : Once this API is ready, please send it across.
I can test it with respect to inbound resources and IOVA reservation
on our platform.

Regards,
Oza.