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

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Message-ID: <CAJZ5v0g0j2fpaHUdvxAkfo-3bRp=GRrKOgespUnz_BqX6timOw@mail.gmail.com>
Date:   Wed, 13 Dec 2023 19:31:11 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, mpearson-lenovo@...ebb.ca
Subject: Re: [PATCH 1/2] PCI: Avoid runtime resuming devices if system is
 shutting down

On Wed, Dec 13, 2023 at 7:27 PM Mario Limonciello
<mario.limonciello@....com> 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@...ebb.ca
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  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?

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