linux-kernel - Why is suspend with s2idle available on POWER8 systems?

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Date:   Sat, 27 Apr 2019 12:53:59 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-pm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Why is suspend with s2idle available on POWER8 systems?

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?

> 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@...er) (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?

For now I disabled the automatic suspend, masking the targets [1].


Kind regards,

Paul


[1]: https://wiki.debian.org/Suspend#Disable_suspend_and_hibernation