pciehp runtime PM

Introduce runtime PM to pciehp in a more thorough and comprehensive way than the reverted 68db9bc81436, taking into account the regressions reported against it.

@Yinghai Lu & Intel/Facebook engineers, I would be grateful if you could test this on as many systems as you can get your hands on, in particular the Skylake servers that were broken by 68db9bc81436. I guess those were Skylake-SP Xeon systems (Purley platform). They're still unreleased and not available outside Intel and their partners. Their release date has been pushed further back to mid-summer. Myself I've only got a puny, 7 years old "Light Ridge" Thunderbolt controller to test with and it doesn't even fully adhere to the PCIe spec.

I'd also be interested to learn if you can measure a drop in power usage on systems with unoccupied hotplug ports.

I've pushed this series to GitHub to ease reviewing:
https://github.com/l1k/linux/commits/pciehp_runpm_v1

Thanks!

Lukas

Lukas Wunner (5):
PCI: pciehp: Resume to D0 on board addition/removal
PCI: pciehp: Remain in D0 while awaiting command completion
PCI: pciehp: Resume to D0 on sysfs read access
PCI: pciehp: Remain in D0 if poll mode is enabled
PCI: Whitelist native hotplug ports for runtime PM

 drivers/pci/hotplug/pciehp_ctrl.c | 13 +++++++++++--
 drivers/pci/hotplug/pciehp_hpc.c  | 25 ++++++++++++++++++++++---
 drivers/pci/pci.c                 |  7 ++-----
 3 files changed, 35 insertions(+), 10 deletions(-)

2.11.0