Hi Adam,
When I try to place the Torpedo DM3730 SOM (w WIFI) into a sleep (standby) state under Mainstream Linux 2018.05.x using 4.4.76, I receive a write error to /sys/power/state. I had modified (and verified) the u-boot optargs environment "no console suspend" was removed using nand unlock, setenv ... and saveenv, reset and printenv optargs. The example you had given under the topic Mainstream DM37x Linux (shown below) could not have been correct in that expected values for state must be 'disk', 'freeze' or 'standby' according to https://01.org/linuxgraphics/gfx-docs/drm/admin-guide/pm/sleep-states.html
modprobe twl4030-pwrbutton
# mount -t debugfs none /sys/kernel/debug
# echo 1 > /sys/kernel/debug/pm_debug/enable_off_mode
# echo 1 > /sys/power/state
sh: write error: Invalid argument
Further, within the make linux-menuconfig one finds the option "Power management options ---> Suspend to RAM and standby" the only enabled option. But if "Hibernation (aka 'suspend to disk') is also enabled, a register /sys/power/disk appears in the rootfs. This suggests that a register '/sys/power/standby' and/or '/sys/power/freeze' is/are missing, resulting in the Invalid argement errors shown below.
# echo 'freeze' > state
sh: write error: Invalid argument
# echo 'suspend' > state
sh: write error: Invalid argument
Has there been a change in the branch 2018.05.x that might cause this? Or perhaps there was a modification on your system at the time that had not been committed?? Any help you could provide me in obtaining a functional standby state on the DM3730 Torpedo (with wifi) would be greatly appreciated.
-William