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

[Stephen Warren <swarren@wwwdotorg.org>]

On 08/14/2012 04:58 PM, Stephen Warren wrote:
> On 08/14/2012 03:55 PM, Bjorn Helgaas wrote:
>> On Tue, Aug 14, 2012 at 12:58 PM, Thierry Reding
>> <thierry.reding@avionic-design.de> 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@wwwdotorg.org> 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.
> 
> 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:

Sigh, that turns out not to work correctly; it solves at least this part
of the problem when booting using device tree, but when booting using a
board file, it causes the IRQ number passed to the PCIe device to be
bogus:-(

I give up for now.