On Thu, Oct 17, 2024 at 09:05:51PM +0530, Krishna chaitanya chundru wrote: > The Controller driver is the parent device of the PCIe host bridge, > PCI-PCI bridge and PCIe endpoint as shown below. > > PCIe controller(Top level parent & parent of host bridge) > | > v > PCIe Host bridge(Parent of PCI-PCI bridge) > | > v > PCI-PCI bridge(Parent of endpoint driver) > | > v > PCIe endpoint driver > > Now, when the controller device goes to runtime suspend, PM framework > will check the runtime PM state of the child device (host bridge) and > will find it to be disabled. So it will allow the parent (controller > device) to go to runtime suspend. Only if the child device's state was > 'active' it will prevent the parent to get suspended. > > It is a property of the runtime PM framework that it can only > follow continuous dependency chains. That is, if there is a device > with runtime PM disabled in a dependency chain, runtime PM cannot be > enabled for devices below it and above it in that chain both at the > same time. > > Since runtime PM is disabled for host bridge, the state of the child > devices under the host bridge is not taken into account by PM framework > for the top level parent, PCIe controller. So PM framework, allows > the controller driver to enter runtime PM irrespective of the state > of the devices under the host bridge. And this causes the topology > breakage and also possible PM issues like controller driver goes to > runtime suspend while endpoint driver is doing some transfers. > > Because of the above, in order to enable runtime PM for a PCIe > controller device, one needs to ensure that runtime PM is enabled for > all devices in every dependency chain between it and any PCIe endpoint > (as runtime PM is enabled for PCIe endpoints). > > This means that runtime PM needs to be enabled for the host bridge > device, which is present in all of these dependency chains. Earlier I asked about how we can verify that no other drivers need a change like the starfive one: https://lore.kernel.org/r/20241012140852.GA603197@bhelgaas I guess this sentence is basically how we verify all drivers are safe with this change? Since this patch adds devm_pm_runtime_enable() in pci_host_probe(), can we expand this along the lines of this so it's more specific about what we need to verify? Every host bridge driver must call pm_runtime_enable() before runtime PM is enabled by pci_host_probe(). Please correct me if that's not the right requirement. > After this change, the host bridge device will be runtime-suspended > by the runtime PM framework automatically after suspending its last > child and it will be runtime-resumed automatically before resuming its > first child which will allow the runtime PM framework to track > dependencies between the host bridge device and all of its > descendants. > > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx> > --- > Changes in v6: > - no change > Changes in v5: > - call pm_runtime_no_callbacks() as suggested by Rafael. > - include the commit texts as suggested by Rafael. > - Link to v4: https://lore.kernel.org/linux-pci/20240708-runtime_pm-v4-1-c02a3663243b@xxxxxxxxxxx/ > Changes in v4: > - Changed pm_runtime_enable() to devm_pm_runtime_enable() (suggested by mayank) > - Link to v3: https://lore.kernel.org/lkml/20240609-runtime_pm-v3-1-3d0460b49d60@xxxxxxxxxxx/ > Changes in v3: > - Moved the runtime API call's from the dwc driver to PCI framework > as it is applicable for all (suggested by mani) > - Updated the commit message. > - Link to v2: https://lore.kernel.org/all/20240305-runtime_pm_enable-v2-1-a849b74091d1@xxxxxxxxxxx > Changes in v2: > - Updated commit message as suggested by mani. > - Link to v1: https://lore.kernel.org/r/20240219-runtime_pm_enable-v1-1-d39660310504@xxxxxxxxxxx > --- > drivers/pci/probe.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 4f68414c3086..8409e1dde0d1 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -3106,6 +3106,11 @@ int pci_host_probe(struct pci_host_bridge *bridge) > pcie_bus_configure_settings(child); > > pci_bus_add_devices(bus); > + > + pm_runtime_set_active(&bridge->dev); > + pm_runtime_no_callbacks(&bridge->dev); > + devm_pm_runtime_enable(&bridge->dev); > + > return 0; > } > EXPORT_SYMBOL_GPL(pci_host_probe); > > -- > 2.34.1 >
