On Thu, Mar 12, 2020 at 03:02:07PM -0700, Kuppuswamy Sathyanarayanan wrote: > On 3/12/20 2:52 PM, Bjorn Helgaas wrote: > > On Thu, Mar 12, 2020 at 02:29:58PM -0700, Kuppuswamy Sathyanarayanan wrote: > > > On 3/12/20 2:02 PM, Austin.Bolen@xxxxxxxx wrote: > > > > On 3/12/2020 2:53 PM, Bjorn Helgaas wrote: > > > > > On Wed, Mar 11, 2020 at 04:07:59PM -0700, Kuppuswamy Sathyanarayanan wrote: > > > > > > On 3/11/20 3:23 PM, Bjorn Helgaas wrote: > > > > > > > Is any synchronization needed here between the EDR path and the > > > > > > > hotplug/enumeration path? > > > > > > If we want to follow the implementation note step by step (in > > > > > > sequence) then we need some synchronization between EDR path and > > > > > > enumeration path. But if it's OK to achieve the same end result by > > > > > > following steps out of sequence then we don't need to create any > > > > > > dependency between EDR and enumeration paths. Currently we follow > > > > > > the latter approach. > > > > > What would the synchronization look like? > > > > > > > > > > Ideally I think it would be better to follow the order in the > > > > > flowchart if it's not too onerous. That will make the code easier to > > > > > understand. The current situation with this dependency on pciehp and > > > > > what it will do leaves a lot of things implicit. > > > > > > > > > > What happens if CONFIG_PCIE_EDR=y but CONFIG_HOTPLUG_PCI_PCIE=n? > > > > > > > > > > IIUC, when DPC triggers, pciehp is what fields the DLLSC interrupt and > > > > > unbinds the drivers and removes the devices. If that doesn't happen, > > > > > and Linux clears the DPC trigger to bring the link back up, will those > > > > > drivers try to operate uninitialized devices? > > > > > > > > > > Does EDR need a dependency on CONFIG_HOTPLUG_PCI_PCIE? > > > > From one of Sathya's other responses: > > > > > > > > "If hotplug is not supported then there is support to enumerate > > > > devices via polling or ACPI events. But a point to note > > > > here is, enumeration path is independent of error handler path, and > > > > hence there is no explicit trigger or event from error handler path > > > > to enumeration path to kick start the enumeration." > > > > > > > > The EDR standard doesn't have any dependency on hot-plug. It sounds like > > > > in the current implementation there's some manual intervention needed if > > > > hot-plug is not supported? > > > > > > No, there is no need for manual intervention even in non hotplug > > > cases. > > > > > > For ACPI events case, we would rely on ACPI event to kick start the > > > enumeration. And for polling model, there is an independent polling > > > thread which will kick start the enumeration. > > > I'm guessing the ACPI case works via hotplug_is_native(): if > > CONFIG_HOTPLUG_PCI_PCIE=n, pciehp_is_native() returns false, and > > acpiphp manages hotplug. > > > > What if CONFIG_HOTPLUG_PCI_ACPI=n also? > > If none of the auto scans are enabled then we might need some > manual trigger (rescan). But this would be needed in native > DPC case as well. > > > > Where is the polling thread? > > drivers/pci/hotplug/pciehp_hpc.c Only if CONFIG_HOTPLUG_PCI_PCIE=y, obviously. My question is about what happens when CONFIG_HOTPLUG_PCI_PCIE=n. I'm not as concerned about requiring a manual rescan. That's inconvenient, but doesn't seem like a big deal because that's what you expect with no hotplug driver. What I *am* worried about is calling driver callbacks on a device that has been reset but not initialized. That could cause all sorts of havoc because the driver thinks it can trust BARs and other configuration.
