Re: [PATCH v3] PCI: Enable runtime pm of the host bridge

[Krishna Chaitanya Chundru]

On 6/11/2024 12:04 AM, Mayank Rana wrote:
> On 6/8/2024 8:14 PM, 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.
> >
> > 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.
> >
> > So enable runtime PM for the host bridge, so that controller driver
> > goes to suspend only when all child devices goes to runtime suspend.
> >
> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@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 v3: 
> > 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 | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 20475ca30505..b7f9ff75b0b3 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -3108,6 +3108,10 @@ 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_enable(&bridge->dev);
> Can you consider using devm_pm_runtime_enable() instead of 
> pm_runtime_enable() ?
> It serves calling pm_runtime_disable() when bridge device is removed as 
> seeing pcie driver is using pci_host_probe() after allocating bridge 
> device, and as part of pcie driver removal calls pci_remove_host_bus(), 
> and bridge device would be freed, but it doesn't call 
> pm_runtime_disable() on it. I don't see any specific functionality issue 
> here as bridge device would be freed anyway, although as we have way to 
> undo what is probe() is doing when bridge device is binding with bridge 
> device. Perhaps we can use available mechanism.
>
> Regards,
> Mayank
Sure I will add as suggested in my next patch.

- Krishna Chaitanya
> >       return 0;
> >   }
> >   EXPORT_SYMBOL_GPL(pci_host_probe);
> >
> > ---
> > base-commit: 30417e6592bfc489a78b3fe564cfe1960e383829
> > change-id: 20240609-runtime_pm-7e6de1190113
> >
> > Best regards,