Re: [PATCH 1/2] PCI: Avoid runtime resuming devices if system is shutting down

[Mario Limonciello]

On 12/13/2023 12:31, Rafael J. Wysocki wrote:
> On Wed, Dec 13, 2023 at 7:27 PM Mario Limonciello
> <mario.limonciello@xxxxxxx> wrote:
> > When the system is going to S5 resuming devices is unnecessary at
> > best and may cause problems for power consumption at S5 at worst.
> >
> > Check the target `system_state` in the pci driver shutdown() callback
> > and skip the runtime resume step if the system is being powered off.
> >
> > Cc: mpearson-lenovo@xxxxxxxxx
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> >   drivers/pci/pci-driver.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > index 51ec9e7e784f..5a6f7a786952 100644
> > --- a/drivers/pci/pci-driver.c
> > +++ b/drivers/pci/pci-driver.c
> > @@ -507,7 +507,9 @@ static void pci_device_shutdown(struct device *dev)
> >          struct pci_dev *pci_dev = to_pci_dev(dev);
> >          struct pci_driver *drv = pci_dev->driver;
> >
> > -       pm_runtime_resume(dev);
> > +       /* If system will go to S5, don't wake up PCI devices for shutdown */
> > +       if (system_state != SYSTEM_POWER_OFF)
> > +               pm_runtime_resume(dev);
>
> What's the guarantee that the driver's shutdown callback will not
> access MMIO regions of a runtime-suspended device?

This is something that may need to be audited.

I have an expectation that drivers will runtime resume a device before 
they try to access it.

> >          if (drv && drv->shutdown)
> >                  drv->shutdown(pci_dev);
> > --