[PATCH v2 1/3] PM: Use hibernate flows for system power off

[Rafael J. Wysocki]

On Wed, May 14, 2025 at 9:34 PM Mario Limonciello <superm1 at kernel.org> wrote:
>
> From: Mario Limonciello <mario.limonciello at amd.com>
>
> When the system is powered off the kernel will call device_shutdown()
> which will issue callbacks into PCI core to wake up a device and call
> it's shutdown() callback.  This will leave devices in ACPI D0 which can
> cause some devices to misbehave with spurious wakeups and also leave some
> devices on which will consume power needlessly.
>
> The issue won't happen if the device is in D3 before system shutdown, so
> putting device to low power state before shutdown solves the issue.
>
> ACPI Spec 6.5, "7.4.2.5 System \_S4 State" says "Devices states are
> compatible with the current Power Resource states. In other words, all
> devices are in the D3 state when the system state is S4."
>
> The following "7.4.2.6 System \_S5 State (Soft Off)" states "The S5
> state is similar to the S4 state except that OSPM does not save any
> context." so it's safe to assume devices should be at D3 for S5.
>
> To accomplish this, modify the PM core to call all the device hibernate
> callbacks when turning off the system when the kernel is compiled with
> hibernate support. If compiled without hibernate support or hibernate fails
> fall back into the previous shutdown flow.
>
> Cc: AceLan Kao <acelan.kao at canonical.com>
> Cc: Kai-Heng Feng <kaihengf at nvidia.com>
> Cc: Mark Pearson <mpearson-lenovo at squebb.ca>
> Cc: Merthan Karakaş <m3rthn.k at gmail.com>
> Tested-by: Denis Benato <benato.denis96 at gmail.com>
> Link: https://lore.kernel.org/linux-pci/20231213182656.6165-1-mario.limonciello@amd.com/
> Link: https://lore.kernel.org/linux-pci/20250506041934.1409302-1-superm1@kernel.org/
> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
> ---
> v2:
>  * Handle failures to hibernate (fall back to shutdown)
>  * Don't use dedicated events
>  * Only allow under CONFIG_HIBERNATE_CALLBACKS
> ---
>  kernel/reboot.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index ec087827c85cd..52f5e6e36a6f8 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -13,6 +13,7 @@
>  #include <linux/kexec.h>
>  #include <linux/kmod.h>
>  #include <linux/kmsg_dump.h>
> +#include <linux/pm.h>
>  #include <linux/reboot.h>
>  #include <linux/suspend.h>
>  #include <linux/syscalls.h>
> @@ -305,6 +306,17 @@ static void kernel_shutdown_prepare(enum system_states state)
>                 (state == SYSTEM_HALT) ? SYS_HALT : SYS_POWER_OFF, NULL);
>         system_state = state;
>         usermodehelper_disable();
> +#ifdef CONFIG_HIBERNATE_CALLBACKS
> +       if (dpm_suspend_start(PMSG_HIBERNATE))
> +               goto resume_devices;

A failure of one device may trigger a cascade of failures when trying
to resume devices and it is not even necessary to resume the ones that
have been powered off successfully.

IMV this should just ignore errors during the processing of devices,
so maybe introduce PMSG_POWEROFF for it?

It should also ignore wakeup events that occur while devices are powered off.

> +       if (dpm_suspend_end(PMSG_HIBERNATE))
> +               goto resume_devices;
> +       return;
> +
> +resume_devices:
> +       pr_emerg("Failed to power off devices, using shutdown instead.\n");
> +       dpm_resume_end(PMSG_RESTORE);

Unfortunately, PMSG_RESTORE is not the right resume action for
PMSG_HIBERNATE because it may not power-up things (some drivers assume
that the restore kernel will power-up devices and so they don't do it
in "restore" callbacks).

I do realize that hibernation uses it to reverse PMSG_HIBERNATE, but
it should not do that either.  That may be fixed later, though.

> +#endif
>         device_shutdown();
>  }
>  /**
> --

I'd prefer to get back to this series after the 6.16 merge window
starts.  It is sort of last minute for 6.16 and it is far from ready
IMV.

Thanks!