Why is suspend with s2idle available on POWER8 systems?

[Rafael J. Wysocki]

On Sat, Apr 27, 2019 at 12:54 PM Paul Menzel <pmenzel at molgen.mpg.de> wrote:
>
> Dear Linux folks,
>
>
> Updating an IBM S822LC from Ubuntu 18.10 to 19.04 some user space stuff
> seems to have changed, so that going into sleep/suspend is enabled.
>
> That raises two questions.
>
> 1.  Is suspend actually supported on a POWER8 processor?

Suspend-to-idle is a special variant of system suspend that does not
depend on any special platform support.  It works by suspending
devices and letting all of the CPUs in the system go idle (hence the
name).

Also see https://www.kernel.org/doc/html/latest/admin-guide/pm/sleep-states.html#suspend-to-idle

>
> > Apr 27 10:18:13 power NetworkManager[7534]: <info>  [1556353093.7224] manager: sleep: sleep requested (sleeping: no  e
> > Apr 27 10:18:13 power systemd[1]: Reached target Sleep.
> > Apr 27 10:18:13 power systemd[1]: Starting Suspend...
> > Apr 27 10:18:13 power systemd-sleep[82190]: Suspending system...
> > Apr 27 10:18:13 power kernel: PM: suspend entry (s2idle)
> > -- Reboot --
>
> > $ uname -m
> > ppc64le
> > $ more /proc/version
> > Linux version 5.1.0-rc6+ (joey at power) (gcc version 8.3.0 (Ubuntu 8.3.0-6ubuntu1)) #1 SMP Sat Apr 27 10:01:48 CEST 2019
> > $ more /sys/power/mem_sleep
> > [s2idle]
> > $ more /sys/power/state
> > freeze mem
> > $ grep _SUSPEND /boot/config-5.0.0-14-generic # also enabled in Ubuntu’s configuration
> > CONFIG_ARCH_SUSPEND_POSSIBLE=y
> > CONFIG_SUSPEND=y
> > CONFIG_SUSPEND_FREEZER=y
> > # CONFIG_SUSPEND_SKIP_SYNC is not set
> > # CONFIG_PM_TEST_SUSPEND is not set
>
> Should the Kconfig symbol `SUSPEND` be selectable? If yes, should their
> be some detection during runtime?
>
> 2.  If it is supported, what are the ways to getting it to resume? What
> would the IPMI command be?

That would depend on the distribution.

Generally, you need to set up at least one device to generate wakeup interrupts.

The interface to do that are the /sys/devices/.../power/wakeup files,
but that has to cause enble_irq_wake() to be called for the given IRQ,
so some support in the underlying drivers need to be present for it to
work.

USB devices generally work as wakeup sources if the controllers reside
on a PCI bus, for example.

Thanks,
Rafael