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

[Bjorn Helgaas <bhelgaas@xxxxxxxxxx>]

On Tue, Aug 14, 2012 at 12:58 PM, Thierry Reding
<thierry.reding@xxxxxxxxxxxxxxxxx> wrote:
> On Tue, Aug 14, 2012 at 01:39:23PM -0600, Stephen Warren wrote:
>> On 08/13/2012 05:18 PM, Bjorn Helgaas wrote:
>> > On Mon, Aug 13, 2012 at 11:47 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
>> ...
>> >> whereas for a device tree boot:
>> >>
>> >> (same):
>> >>> [    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)
>> >>> [    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)
>> >>> [    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.

> Maybe pci_scan_root_bus() should be calling pci_bus_assign_resources()?
> Or a new function could be added which also assigns the resources.

Yes, it probably should.  I'm nervous about just throwing it in there
without quite a bit more analysis, but that's definitely the direction
I think we should be heading.

Bjorn
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