i.MX6 PCIe support

[Andrey Smirnov]

>> However when I boot Linux kernel (with 'igb' driver patched to
>> recognize 8086:1531 VID:PID) on that board and run 'eepromARMtool'
>> (Intel provided EEPROM programming tool) I can see it reading various
>> registers correctly
>>
>> My questions are:
>>    - Is anyone currently using i.MX6 PCIe driver in 'next' branch?
>
> I didn't try the latest revision, but with v2015.10.0 PCIe on i.MX6 was
> working fine.
>
>>    - Has anyone seen similar behavior on this particular controller
>> and discovered the root cause?
>>
> The symptoms you describe do look to me like the firmware on the i210
> device doesn't get initialized. Unfortunately I don't have any specific
> pointers where to start searching for the root cause.
>

I kept looking into the issue and noticed one thing that Linux kernel
does differently -- when handling PCI bridges it allocates bridge
window before that PCI bridge's BAR windows in address space as can be
seen below:

[    0.831099] imx6q-pcie 1ffc000.pcie: PCI host bridge to bus 0000:00
[    0.837480] pci_bus 0000:00: root bus resource [io  0x1000-0x10000]
[    0.843878] pci_bus 0000:00: root bus resource [mem 0x01000000-0x01efffff]
[    0.850881] pci_bus 0000:00: root bus resource [bus 00-ff]
[    0.856913] PCI: bus0: Fast back to back transfers disabled
[    0.880182] PCI: bus1: Fast back to back transfers disabled
[    0.885980] pci 0000:00:00.0: BAR 8: assigned [mem 0x01000000-0x01bfffff]
[    0.892902] pci 0000:00:00.0: BAR 0: assigned [mem 0x01c00000-0x01cfffff]
[    0.899806] pci 0000:00:00.0: BAR 6: assigned [mem
0x01d00000-0x01d0ffff pref]
[    0.907154] pci 0000:00:00.0: BAR 7: assigned [io  0x1000-0x1fff]
[    0.913387] pci 0000:01:00.0: BAR 0: assigned [mem 0x01000000-0x017fffff]
[    0.920324] pci 0000:01:00.0: BAR 3: assigned [mem 0x01800000-0x01803fff]
[    0.927241] pci 0000:01:00.0: BAR 2: assigned [io  0x1000-0x101f]
[    0.933480] pci 0000:00:00.0: PCI bridge to [bus 01]
[    0.938553] pci 0000:00:00.0:   bridge window [io  0x1000-0x1fff]
[    0.944772] pci 0000:00:00.0:   bridge window [mem 0x01000000-0x01bfffff]
[    0.951984] pcieport 0000:00:00.0: Signaling PME through PCIe PME interrupt
[    0.959056] pci 0000:01:00.0: Signaling PME through PCIe PME interrupt


When I tried emulating this behavior in Barebox by moving
"setup_device(dev, 2)" from line 384 to be right after
"postscan_setup_bridge(dev)" in "drivers/pci/pci.c" I was able to
communicate with i210.

I am bit hesitant to make a patch yet, since for the life of me I
cannot explain this behavior, any thoughts on why this can be
happening?

Andrey