Power Modes

i.mx6 supports three different power save modes:

PM mode	Comment	Restrictions

PM mode

Comment

Restrictions

freeze

also known as Suspend-to-Idle

Wake-on-LAN not supported, NXP Errata ERR006687

standby

switch IO-devices to low power mode, disable all but first CPU

Wake-on-LAN not supported, NXP Errata ERR006687

suspend

also known as Suspend-to-RAM (S3).
Backplane is powered off via Q7 pin18 (SUS_S3#)

This is the default power safe mode on conga-QMX6

Details on the different power save modes can be found on kernel documentation, e.g:

https://github.com/torvalds/linux/blob/v5.15/Documentation/admin-guide/pm/sleep-states.rst

Power Management IO on edge-connector or backplane

There are three buttons on the backplane which are related to the power management. Also a pin on Q7 edge connector is available to indicate the power save mode.

Button	i.mx6 GPIO	Type	Q7-pin	Q7-signal	comment

Button	i.mx6 GPIO	Type	Q7-pin	Q7-signal	comment
Power Button	GPIO3_29	Input	20	PWRBTN#	external pullup on module plus external PWRBTN curcuit
Suspend Button	GPIO4_7	Input	21	SLP_BTN#	external pullup on module
Lid Switch	GPIO4_66	Input	22	LID_BTN#	external pullup on module
SUS_S3	GPIO1_5	Output	18	SUS_S3#	external buffer / SUS_S3 curcuit, pulldown on Q7-pin

All three buttons/switches are configured as wakeup source, so it is possible to wakeup from suspend either via suspend key or power key.

Switch to Power-Save mode

To freeze/suspend-to-idle

# echo freeze > /sys/power/state

To standby

# echo standby > /sys/power/state

To suspend/ suspend to RAM

# systemctl suspend

Remark:

do not enable suspend via power interface in sysfs, e.g. do not "echo mem > /sys/power/state" and wakeup afterwards with power button!
Systemd handles the power button and after wakeup with power button and the system is shutting down immediately because systemd had no chance to realize the suspend (no hooks are processed via kernel api calls in sysfs) and handles the power button event as a power off signal.
Details on sysfs-interface: https://github.com/torvalds/linux/blob/v5.15/Documentation/ABI/testing/sysfs-power

Another possibility to enter suspend mode is to press the suspend button on backplane and release it.

Wakeup

Via backplane button

This works out of the box. Just switch to suspend mode and then press power button or suspend button

Via serial console

Afterwards press a button on keyboard in serial debug console to wakeup.

Via Wake-On-LAN

# ethtool -s eth0 wol g
# systemctl suspend

Then send from another computer in the same network the magic packet via:

# etherwake -i <ETH_INTERFACE> -D <MAC_ADDRESS_OF_CONGA_QMX6_MODULE>

Example:

Via Wake-On-USB

connect usb device and check via "lsusb" bus and identify it.

Enable wake from USB device:

# echo enabled > /sys/bus/platform/devices/2184200.usb/power/wakeup
# echo enabled > /sys/bus/platform/devices/20ca000.usbphy/power/wakeup
# echo enabled > /sys/bus/platform/devices/ci_hdrc.1/power/wakeup
# echo enabled > /sys/bus/usb/devices/1-1/power/wakeup
# echo enabled > /sys/bus/usb/devices/1-1.3/power/wakeup

The last two commands depend on the USB slot on which the wakeup source (i.e. mouse/keyboard) is connected. In the example above this is bus "1-1" and the device got "1-1.3". Watch syslog when connecting the device for details.

ATTENTION.

On QMX6 only USB #2 and #3 are powered in S3 and are able to support wake-on-usb. On QEVA backplane this ports are at CN7 (below the network connector).

3: Then enter suspend mode

# systemctl suspend

Check with keyboard / mouse button press