Re: [PATCH 2/4] pcie: update slot power status only is power control is enabled

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 25, 2022 at 11:12:59AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> >    pcie_cap_slot_post_load()
> >        -> pcie_cap_update_power()
> >            -> pcie_set_power_device()
> >                -> pci_set_power()
> >                    -> pci_update_mappings()
> 
> > Fix it by honoring PCI_EXP_SLTCAP_PCP and updating power status
> > only if capability is enabled.
> 
> > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > index d7d73a31e4..2339729a7c 100644
> > --- a/hw/pci/pcie.c
> > +++ b/hw/pci/pcie.c
> > @@ -383,10 +383,9 @@ static void pcie_cap_update_power(PCIDevice *hotplug_dev)
> >  
> >      if (sltcap & PCI_EXP_SLTCAP_PCP) {
> >          power = (sltctl & PCI_EXP_SLTCTL_PCC) == PCI_EXP_SLTCTL_PWR_ON;
> > +        pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> > +                            pcie_set_power_device, &power);
> >      }
> > -
> > -    pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> > -                        pcie_set_power_device, &power);
> >  }
> 
> The change makes sense, although I don't see how that changes qemu
> behavior.
> 
> 'power' defaults to true, so when SLTCAP_PCP is off it should never
> ever try to power off the devices.  And pci_set_power() should figure
> the state didn't change and instantly return without touching the
> device.
> 
> take care,
>   Gerd

And making sure power is actually up might be a bit cleaner just in
case down the road we start plugging devices in a powered off state.

-- 
MST