If you are using one of these adapters, you may need to change the /boot/boot.src.txt file from:

setenv baseconfig ahci_imx.hotplug=1 raid=noautodetect telnet root=/dev/mmcblk0p2 video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 rootwait consoleblank=0 selinux=0 nohdparm splash

setenv baseconfig ahci_imx.hotplug=1 raid=noautodetect telnet root=/dev/mmcblk0p2 video=mxcfb0:dev=hdmi,1280x720M@60,if=RGB565 rootwait consoleblank=0 selinux=0 nohdparm splash

If you video mode is incorrect, it can result in a reboot loop.

To enable the serial console, add console=ttymxc0,115200 to the command line, after setenv baseconfig. The third line in /boot/boot.src.txt should look something like this:

setenv baseconfig console=ttymxc0,115200 coherent_pool=1M rw ahci_imx.hotplug=1 raid=noautodetect telnet root=/dev/mmcblk0p2 video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 rootwait consoleblank=0 selinux=0 nohdparm splash dmfc=3

To enable a terminal on the serial console, copy the file /etc/init/tty1.conf to /etc/init/tty3.conf. Edit the last line in the new file, replace tty1 with ttymxc0, and 38400 with 115200. It should look like this:

exec /sbin/getty -8 115200 ttymxc0