staging: mt7621-pci: factor out 'mt7621_pcie_enable_port' function

[Greg Ungerer]

Hi Sergio,

I am working on a couple of different MedaiTek MT7621 based platforms
and am having problems with the PCI bus on those.

Big picture is that the PCI bus on my boards worked in linux-4.20
(with the obvious compilation breakage fixed), and it does not work
in linux-5.0 or linux-5.1.

On linux-4.20 the PCI bus probe at kernel boot looks like this:

***** Xtal 40MHz *****
PCIE1 no card, disable it(RST&CLK)
PCIE2 no card, disable it(RST&CLK)
PCIE0 enabled
PCI coherence region base: 0x60000000, mask/settings: 0xf0000002
mt7621-pci 1e140000.pcie: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [io  0xffffffff]
pci_bus 0000:00: root bus resource [mem 0x60000000-0x6fffffff]
pci_bus 0000:00: root bus resource [bus 00-ff]
pci 0000:00:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
pci 0000:00:00.0: PCI bridge to [bus 01-ff]
pci 0000:00:00.0: BAR 0: no space for [mem size 0x80000000]
pci 0000:00:00.0: BAR 0: failed to assign [mem size 0x80000000]
pci 0000:00:00.0: BAR 8: assigned [mem 0x60000000-0x601fffff]
pci 0000:00:00.0: BAR 9: assigned [mem 0x60200000-0x602fffff pref]
pci 0000:00:00.0: BAR 1: assigned [mem 0x60300000-0x6030ffff]
pci 0000:00:00.0: BAR 7: no space for [io  size 0x1000]
pci 0000:00:00.0: BAR 7: failed to assign [io  size 0x1000]
pci 0000:01:00.0: BAR 0: assigned [mem 0x60000000-0x601fffff 64bit]
pci 0000:01:00.0: BAR 6: assigned [mem 0x60200000-0x6020ffff pref]
pci 0000:00:00.0: PCI bridge to [bus 01]
pci 0000:00:00.0:   bridge window [mem 0x60000000-0x601fffff]
pci 0000:00:00.0:   bridge window [mem 0x60200000-0x602fffff pref]

The PCI bus works, and devices on it are found and work as expected.

On linux-5.1 the PCI initialization and probe fails, with the kernel
locking up:

...
mt7621-pci 1e140000.pcie: Port 454043648 N_FTS = 0
mt7621-pci-phy 1e149000.pcie-phy: Xtal is 40MHz
mt7621-pci 1e140000.pcie: pcie0 no card, disable it (RST & CLK)
mt7621-pci 1e140000.pcie: Initiating port 0 failed
mt7621-pci 1e140000.pcie: Port 454043648 N_FTS = 1
mt7621-pci-phy 1e149000.pcie-phy: Xtal is 40MHz
mt7621-pci 1e140000.pcie: pcie1 no card, disable it (RST & CLK)
mt7621-pci 1e140000.pcie: Initiating port 1 failed
mt7621-pci 1e140000.pcie: Port 454043648 N_FTS = 2
mt7621-pci-phy 1e14a000.pcie-phy: Xtal is 40MHz
mt7621-pci 1e140000.pcie: pcie2 no card, disable it (RST & CLK)

The lockup is in mt7621_pci_phy_power_off(), at the phy_read() call.
If I modify that code and return immediately in that mt7621_pci_phy_power_off()
the systemboots - but obviously from the above you can see that the PCI bus
and no devices were detected.

Copying in the working linux-4.20 pci-mt7621.c into place on
linux-5.1 results in a working PCI bus also. I have 2 very different
MT7621 based boards, and they both exhibit this same problem.

I tried bisecting that back to find the problem commit.
It was not at all easy with quite a few of the mt7621 PCI related
patches not building in isolation while bisecting. But ultimately
I got to commit 745eeeac68d7 ("staging: mt7621-pci: factor out
'mt7621_pcie_enable_port' function").

Any idea what might be going wrong here?

Regards
Greg