Re: [PATCH] PCI: Power on bridges before scanning new devices

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, May 25, 2016 at 12:13:09AM +0300, Mika Westerberg wrote:
> On Tue, May 24, 2016 at 03:53:23PM +0300, Mika Westerberg wrote:
> > > I dropped "ACPI / hotplug / PCI: Runtime resume bridge before rescan"
> > > on the assumption that "PCI: Power on bridges before scanning new
> > > devices" is sufficient to cover both the ACPI and the generic PCi
> > > rescan cases, but I'd like some reassurance about that.
> > 
> > I agree with your reasoning that the patch should not be needed anymore.
> > However, I have the machine which needed that patch at home so I'm not
> > able to test it now. I'll do that later today when I get back home.
> 
> I tried now on my Lenovo Yoga 900 laptop and unfortunately "PCI: Power
> on bridges before scanning new devices" seems not to be enough. This
> machine has SD-card reader connected to one PCIe port and once I unload
> the sdhci-pci driver and enable runtime PM for the device, next system
> suspend/resume cycle loses the SD-card reader PCI device.
> 
> I will investigate more tomorrow -- it is getting late here.

I think I found reason for the issue.

When the laptop resumes it will send ACPI BUS_CHECK event for the two
PCIe root ports. This ends up in acpiphp_check_bridge() where it goes
through all slots in that bridge checking if the devices are still
present. This happens before we call pci_scan_bridge() for the bridge
itself.

Since the bridge is in D3 config space of the device behind it is not
available and we determine that the device is not there anymore.

It looks like we either need that ACPI hotplug patch or alternatively we
could add pm_runtime_get/put() in acpiphp_check_bridge().