Why is suspend with s2idle available on POWER8 systems?

[Paul Menzel]

Dear Rafael,


On 04/29/2019 09:17 AM, Rafael J. Wysocki wrote:
> On Sat, Apr 27, 2019 at 12:54 PM Paul Menzel <pmenzel at molgen.mpg.de> wrote:

>> 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

Thanks. I guess I mixed it up with the new S0ix-states [1].

>>> 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.

```
$ find /sys/devices/ -name wakeup | xargs grep enabled
/sys/devices/pci0021:00/0021:00:00.0/0021:01:00.0/0021:02:09.0/0021:0d:00.0/usb1/1-3/1-3.4/power/wakeup:enabled
/sys/devices/pci0021:00/0021:00:00.0/0021:01:00.0/0021:02:09.0/0021:0d:00.0/power/wakeup:enabled
$ lsusb -t
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
    |__ Port 3: Dev 2, If 0, Class=Hub, Driver=hub/5p, 480M
        |__ Port 1: Dev 3, If 0, Class=Mass Storage, Driver=usb-storage, 480M
        |__ Port 2: Dev 4, If 0, Class=Mass Storage, Driver=usb-storage, 480M
        |__ Port 3: Dev 5, If 0, Class=Mass Storage, Driver=usb-storage, 480M
        |__ Port 4: Dev 6, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
        |__ Port 4: Dev 6, If 1, Class=Human Interface Device, Driver=usbhid, 1.5M
$ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 006: ID 046b:ff10 American Megatrends, Inc. Virtual Keyboard and Mouse
Bus 001 Device 005: ID 046b:ff31 American Megatrends, Inc. 
Bus 001 Device 004: ID 046b:ff40 American Megatrends, Inc. 
Bus 001 Device 003: ID 046b:ff20 American Megatrends, Inc. 
Bus 001 Device 002: ID 046b:ff01 American Megatrends, Inc. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
```


Kind regards,

Paul


[1]: https://01.org/blogs/qwang59/2018/how-achieve-s0ix-states-linux

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