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

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On 08/13/2012 11:40 AM, Thierry Reding wrote:
> On Mon, Aug 06, 2012 at 01:42:21PM -0600, Stephen Warren wrote:
>> On 07/26/2012 01:55 PM, Thierry Reding wrote:
>>> This patch series adds support for device tree based probing of
>>> the PCIe controller found on Tegra SoCs.
>> 
>> Thierry, I just tested all Tegra boards in v3.6-rc1, and noticed
>> that PCIe doesn't work on TrimSlice when booting use device tree.
>> I think I found the cause, and I can't see why the same problem
>> doesn't affect this series. Perhaps you can enlighten me?
...
>> PCI: Device 0000:01:00.0 not available because of resource
>> collisions
...
> I've looked into this a bit, and it seems like ARM is using an
> open- coded version of the pci_enable_resources() function here,
> with the only difference being the unconditional enabling of both
> I/O and memory- mapped access for bridges. On Tegra there is
> already a PCI fixup to do this, so pci_enable_resources() can be
> used as-is. I came up with the attached patch but haven't been able
> to test it yet.

Thanks very much for looking into this.

The patch did alter the behavior a little for TrimSlice, but didn't
solve the problem. The old error messages:

> [    2.173971] PCI: Device 0000:01:00.0 not available because of resource collisions
> [    2.181453] r8169 0000:01:00.0: (unregistered net_device): enable failure
> [    2.188254] r8169: probe of 0000:01:00.0 failed with error -22

Were replaced with the following with your patch:

> [    2.174010] r8169 0000:01:00.0: device not available (can't reserve [io  0x0000-0x00ff])
> [    2.182098] r8169 0000:01:00.0: (unregistered net_device): enable failure
> [    2.188900] r8169: probe of 0000:01:00.0 failed with error -22

This message appears from drivers/pci/setup-res.c pci_enable_resources()
due to:

> 		if (!r->parent) {
> 			dev_err(&dev->dev, "device not available "
> 				"(can't reserve %pR)\n", r);
> 			return -EINVAL;
> 		}

That check doesn't appear in ARM's custom pcibios_enable_device().
Disabling that check yields:

> [    2.174192] r8169 0000:01:00.0: enabling device (0140 -> 0143)
> [    2.180041] r8169 0000:01:00.0: BAR 2: can't reserve [mem 0x00000000-0x00000fff 64bit pref]
> [    2.188386] r8169 0000:01:00.0: (unregistered net_device): could not request regions
> [    2.196140] r8169: probe of 0000:01:00.0 failed with error -16

I think that's because the pci_dev's resources are initially assigned
PCI-aperture-relative addresses, and then these are later patched up to
take account of where the aperture is mapped into the CPU's address space.

Boot log using board files:

> [    1.146145] pci 0000:01:00.0: reg 10: [io  0x0000-0x00ff]
> [    1.151745] pci 0000:01:00.0: reg 18: [mem 0x00000000-0x00000fff 64bit pref]
> [    1.159007] pci 0000:01:00.0: reg 20: [mem 0x00000000-0x00003fff 64bit pref]
> [    1.166270] pci 0000:01:00.0: reg 30: [mem 0x00000000-0x0001ffff pref]
...
> [    1.217829] pci 0000:01:00.0: BAR 6: assigned [mem 0xa0000000-0xa001ffff pref]
> [    1.225264] pci 0000:01:00.0: BAR 4: assigned [mem 0xa0020000-0xa0023fff 64bit pref]
> [    1.233236] pci 0000:01:00.0: BAR 2: assigned [mem 0xa0024000-0xa0024fff 64bit pref]
> [    1.241206] pci 0000:01:00.0: BAR 0: assigned [io  0x1000-0x10ff]
... (I added some extra printks:)
> [    1.488007] r8169 0000:01:00.0: BAR 0: requesting [io  0x1000-0x10ff]
> [    1.501483] r8169 0000:01:00.0: BAR 2: requesting [mem 0xa0024000-0xa0024fff 64bit pref]
> [    1.516611] r8169 0000:01:00.0: BAR 4: requesting [mem 0xa0020000-0xa0023fff 64bit pref]

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.

Does anyone know where/what that "probe now" vs. "probe later" decision
point is? I'll try and track it down if nobody beats me to it.
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