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

[Rafael J. Wysocki]

On Wed, Dec 13, 2023 at 7:33 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
>
> 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.

But they don't need to do it, because the core does it right now,
which is my point.