[PATCH] PCI: Check whether bridges allow access to extended config space

Hi,

Gilles Buloz wrote:

Here are full dmesg + lspci -vv + ... for the following cases :
- 4.17-rc1_probe_failed_without_pcieaspmoff.txt : I get a broken PCI config at most boots, without pcie_aspm=off
- 4.17-rc1_probe_ok_without_pcieaspmoff.txt : I get a correct PCI config at some boots, even without pcie_aspm=off
- 4.17-rc1_probe_always_ok_with_pcieaspmoff.txt : I get a correct PCI config at all boots when using pcie_aspm=off
- 4.1.35_probe_always_ok_without_pcieaspmoff.txt : I get a correct PCI config at all boots when using kernel 4.1.35-rt41 (from NXP
Yocto BSP), even without pcie_aspm=off

I noticed these strange things :
- with 4.17-rc1, without pcie_aspm=off, the kernel is hanging during ~1 second :
    - before line "ASPM: Could not configure common clock" when PCI config is OK
    - or before line "bridge configuration invalid ([bus ff-ff]), reconfiguring" when PCI config is NOT OK
      (the FFs in "[bus ff-ff]" seems side effects of read returning ~0 because device is off)
- no such hang when pcie_aspm=off is used
- applying reverse patch for "PCI/ASPM: Don't warn if already in common clock mode"
    (commit 04875177dbe034055f23960981ecf6fb8ea1d638) does not give more message

I submitted this as a bug here:
https://bugzilla.kernel.org/show_bug.cgi?id=199671

Thanks,
Fred