iMX6Q reboot hangs issue

[caritzhu]

I use "fsl-yocto-L4.1.15_2.0.0-ga" BSP of imx6q. However, when I enter reboot command, the debug port shows as the following:

root@imx6qsabresd:~# reboot

The system is going down for reboot NOW! (ttymxc0) (Mon Jun 12 08:15:47 2017)
INIT: Switching to runlevel: 6
INIT: Sending processes the TERM signal
root@imx6qsabresd:~# Stopping XServer
Stopping Dropbear SSH server: stopped /usr/sbin/dropbear (pid 599)
dropbear.
 * Stopping Avahi mDNS/DNS-SD Daemon: avahi-daemon                                                                         [ ok ]
Stopping advanced power management daemon: no /usr/sbin/apmd found; none killed
apmd.
Stopping atd: OK
Stopping bluetooth
/usr/libexec/bluetooth/bluetoothd
Stopping system message bus: dbus.
stopping mountd: done
stopping nfsd: done
Stopping ntpd: done
Stopping system log daemon...0
Stopping kernel log daemon...0
stopping statd: done
Stopping Connection Manager
Stopping Telephony daemon
ALSA: Storing mixer settings...
/usr/sbin/alsactl: save_state:1595: No soundcards found...
Stopping crond: OK
Stopping rpcbind daemon...
done.
Stopping Linux NFC daemon
Deconfiguring network interfaces... done.
Sending all processes the TERM signal...
logout
Sending all processes the KILL signal...
Unmounting remote filesystems...
Deactivating swap...
Unmounting local filesystems...
EXT4-fs (mmcblk3p2): re-mounted. Opts: (null)
Rebooting... reboot: Restarting system

Then the system hangs and will not reboot at all. Our board is designed based on imx6q sabresd, but without WDOG_B signal connecting to external PMIC. I want to confirm whether it is necessary for the system. BTW we use ldo_enable in our board design.

Thank you everybody!

[igorpadykov]

Hi carit

this is expected behaviour as without without WDOG_B resetting

whole board power, processor may start to boot with lower VDD_ARM_IN

voltages, as cpu freq driver may set it to low values. One can try

to disable cpu freq driver or guarantee valid VDD_ARM_IN value

at reboot by any other ways.

Best regards
igor
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[caritzhu]

Hi igorpadykov,

Thank you for your reply!

I think you are right, the CPU may occur issue when restart with 400M low freq. And if I set cpu freq to be 996MHz by using the command of "echo 996000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq", then reboot could be ok. I think reboot command is easy to fix the issue, that I can change the source code to set the higer freq first then execute the reboot sequence. But If the system hangs by other reason, such as other application crash, this solution can not be active. BTW, we can not set CPU freq higher than 800Mhz all the time.