xen arm64 low power sleep support

[Anthony Chan <anthonychan@xxxxxxxxxx>]

Hi all,

My name is Tony and I've been researching/developing using Xen for potential 
upcoming uses in our embedded systems.  I started with Xen using Xilinx tools 
about a year ago and still have lots to learn about what it can to do in the 
embedded space.  So far, I've managed to integrate Xen and Linux into an 
existing product that exclusively runs bare-metal code on a ZynqMP SoC and 
migrate some of the functionality into custom Linux driver/userspace.

I'm now looking at low power support, for now at least between Xen (4.16) and 
Linux (5.15) dom0.  I've tried a few different Linux kernel configs around 
power management and each time I try to suspend from linux dom0 (via sysfs or 
systemctl), Xen will watchdog on dom0 guest.  AFAIK, Xen should trap on a 'WFI' 
from guests, but from what I can tell debugging through the linux suspend 
process is it's spinning in a 'suspend-to-idle' loop before it can get to 
issuing a 'WFI' or using PSCI interface to notify Xen.  I'm beginning to 
suspect that 'low power' support for embedded arm64 just isn't quite there yet, 
or am I missing something in the configs?

I realize this could very well be a Linux 'issue' but checking here first.  I 
know Xen presents a flattened device tree to Linux without CPU idle-state nodes 
and maybe this is causing the linux guest to only do the suspend-to-idle mode?  
I should mention that I'm booting up using dom0less feature if that matters.

Appreciate the help, thanks.


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