On Fri, Mar 08, 2024 at 08:38:52AM +0530, Krishna Chaitanya Chundru wrote: > On 3/8/2024 3:25 AM, Bjorn Helgaas wrote: > > [+to Rafael, sorry, another runtime PM question, beginning of thread: > > https://lore.kernel.org/r/20240305-runtime_pm_enable-v2-1-a849b74091d1@xxxxxxxxxxx] > > > > On Thu, Mar 07, 2024 at 07:28:54AM +0530, Krishna Chaitanya Chundru wrote: > > > On 3/6/2024 1:27 AM, Bjorn Helgaas wrote: > > > > On Tue, Mar 05, 2024 at 03:19:01PM +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 > > > > > > > > > > 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. > > > > > > > > IIUC this says that we runtime suspend the controller even though > > > > runtime PM is disabled for the host bridge? I have a hard time > > > > parsing this; can you cite a function that does this or some relevant > > > > documentation about how this part of runtime PM works? > > > > > > > Generally controller should go to runtime suspend when endpoint client > > > drivers and pci-pci host bridge drivers goes to runtime suspend as the > > > controller driver is the parent, but we are observing controller driver > > > goes to runtime suspend even when client drivers and PCI-PCI bridge are > > > in active state. > > > > It surprises me that a device could be suspended while children are > > active. A PCI-PCI bridge must be in D0 for any devices below it to be > > active. The controller is a platform device, not a PCI device, but I > > am similarly surprised that we would suspend it when children are > > active, which makes me think we didn't set the hierarchy up correctly. > > > > It doesn't seem like we should need to enable runtime PM for a parent > > to keep it from being suspended when children are active. > > Here we are not enabling runtime PM of the controller device, we are > enabling runtime PM for the bridge device which is maintained by the > PCIe framework. The bridge device is the parent of the PCI-PCI > bridge and child of the controller device. As the bridge device's > runtime PM is not enabled the PM framework is ignoring the child's > runtime status. OK, it's the host bridge, not the controller. I'm still surprised that the PM framework will runtime suspend a device when child devices are active. And further confused about managing the host bridge runtime PM in a controller driver. Which other callers of pci_alloc_host_bridge() or devm_pci_alloc_host_bridge() will need similar changes? > > > > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c > > > > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c > > > > > @@ -16,6 +16,7 @@ > > > > > #include <linux/of_pci.h> > > > > > #include <linux/pci_regs.h> > > > > > #include <linux/platform_device.h> > > > > > +#include <linux/pm_runtime.h> > > > > > > > > > > #include "../../pci.h" > > > > > #include "pcie-designware.h" > > > > > @@ -505,6 +506,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp) > > > > > if (pp->ops->post_init) > > > > > pp->ops->post_init(pp); > > > > > > > > > > + pm_runtime_set_active(&bridge->dev); > > > > > + pm_runtime_enable(&bridge->dev); > > > > > + > > > > > return 0; > > > > > > > > > > err_stop_link:
