Re: [PATCH v3 00/10] ARM: tegra: Add PCIe device tree support

On 08/14/2012 03:55 PM, Bjorn Helgaas wrote:

On Tue, Aug 14, 2012 at 12:58 PM, Thierry Reding
[off-list ref] wrote:

quoted

On Tue, Aug 14, 2012 at 01:39:23PM -0600, Stephen Warren wrote:

quoted

On 08/13/2012 05:18 PM, Bjorn Helgaas wrote:

quoted

On Mon, Aug 13, 2012 at 11:47 AM, Stephen Warren [off-list ref] wrote:

...

quoted

quoted

whereas for a device tree boot:

(same):

quoted

[    2.112217] pci 0000:01:00.0: reg 10: [io  0x0000-0x00ff]
[    2.117635] pci 0000:01:00.0: reg 18: [mem 0x00000000-0x00000fff 64bit pref]
[    2.124690] pci 0000:01:00.0: reg 20: [mem 0x00000000-0x00003fff 64bit pref]
[    2.131731] pci 0000:01:00.0: reg 30: [mem 0x00000000-0x0001ffff pref]

... (request region happens early)

quoted

[    2.179838] r8169 0000:01:00.0: BAR 0: requesting [io  0x0000-0x00ff]
[    2.193312] r8169 0000:01:00.0: BAR 2: requesting [mem 0x00000000-0x00000fff 64bit pref]
[    2.201397] r8169 0000:01:00.0: BAR 2: can't reserve [mem 0x00000000-0x00000fff 64bit pref]
[    2.209742] r8169 0000:01:00.0: (unregistered net_device): could not request regions

... (same, just happens too late)

quoted

[    2.236818] pci 0000:01:00.0: BAR 6: assigned [mem 0xa0000000-0xa001ffff pref]
[    2.244027] pci 0000:01:00.0: BAR 4: assigned [mem 0xa0020000-0xa0023fff 64bit pref]
[    2.251794] pci 0000:01:00.0: BAR 2: assigned [mem 0xa0024000-0xa0024fff 64bit pref]
[    2.259542] pci 0000:01:00.0: BAR 0: assigned [io  0x1000-0x10ff]

I suspect this is all still related to the PCI devices themselves being
probed much earlier in the overall PCI initialization sequence when the
PCI controller is probed later in the boot sequence, whereas PCI device
probe is deferred until the overall PCI initialization sequence is
complete if the PCI controller is probed very early in the boot sequence.

I don't know what to apply your patches to (they don't apply cleanly
to v3.6-rc2), so I can't see exactly what you're doing.  But it looks
like you might be calling pci_bus_add_devices() before
pci_bus_assign_resource(), which isn't going to work.

Yes, that's exactly what is happening.

PCIe initialization starts in arch/arm/mach-tegra/pci.e
tegra_pcie_init() which calls arch/arm/kernel/bios32.c
pci_common_init(). That function first calls pcibios_init_hw() (in the
same file, more about this later) and then loops over PCI buses, calling
amongst other things pci_bus_assign_resources() then pci_bus_add_devices().

The problem is that ARM's pcibios_init_hw() calls pci_scan_root_bus()
(or a host-driver-specific function which that also calls
pci_scan_root_bus() in Tegra's case) which in turn calls
pci_bus_add_devices() right at the end, before control has returned to
pci_common_init() and hence before pci_bus_assign_resources() has been
called.

If I modify pci_scan_root_bus() and remove the call to
pci_bus_add_devices(), everything works as expected.

So, I guess the question is: Should ARM's pcibios_init_hw() not be
calling pci_scan_root_bus(), or at least presumably the ARM PCI code
needs to do things in a slightly different order?

I think you need to do something like this instead of using pci_scan_root_bus():

    pci_create_root_bus()
    pci_scan_child_bus()
    pci_bus_assign_resources()
    pci_bus_add_devices()

This is the effective order used by most of the pci_create_root_bus() callers.

That would pretty much duplicate everything in pci_scan_root_bus(). That
might cause divergence down the road.

Can't we make the call to pci_bus_add_devices() optional in
pci_scan_root_bus() somehow; one of:

* Add a parameter to pci_scan_root_bus() controlling this.

(rather a large patch)

* Split pci_scan_root_bus() into pci_scan_root_bus() and
pci_scan_root_bus_no_add(), such that pci_scan_root_bus() is just a
wrapper that calls pci_scan_root_bus_no_add() then pci_bus_add_devices().

(very simple patch, and the new function can easily be used as/when it's
needed, e.g. enabled just for Tegra in 3.6 to reduce risk of regressions)

* Add a flag to struct pci_bus that requests pci_scan_root_bus() skip
the call to pci_bus_add_devices().

(a flag in the bus struct just for one function seems a little
circuitous, but perhaps OK)

* ifdef out the call to pci_bus_add_devices(), if building for ARM.

(very simple, and probably correct)

Actually, I'm not totally convinced some other archs shouldn't skip this
too; while I couldn't find any other arch that explicitly calls
pci_bus_assign_resources() and pci_bus_add_devices() after
pci_scan_root_bus(), I did see some that call
pci_assign_unassigned_resources() which seems like it might be due to a
similar situation?

* Add another pcibios_*() callback that pci_scan_root_bus() calls to
determine whether to call pci_bus_add_devices(), with default
implementation.