On Fri, Apr 28, 2017 at 02:28:38PM +0200, Arnd Bergmann wrote:

On Wed, Apr 26, 2017 at 1:17 PM, Lorenzo Pieralisi
[off-list ref] wrote:

quoted

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 <redacted>
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.

quoted

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