I copied the sd card to /dev/sda2, then set it to root= and yet:
$this->bbcode_second_pass_code('', 'NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
|-sda1 8:1 0 923.5G 0 part /mnt/Multimedia
`-sda2 8:2 0 8G 0 part
mmcblk0 179:0 0 3.7G 0 disk
`-mmcblk0p1 179:1 0 3.7G 0 part / <---- darn!
')
This is my uEnv:
$this->bbcode_second_pass_code('', 'mmcargs=setenv bootargs root=/dev/sda2 rootwait rw console=tty1 console=ttymxc0,115200 consoleblank=0 video=mxcfb0:dev=hdmi,1920x1080@60,if=RGB24,bpp=32 dmfc=3 ahci_imx.hotplug=1 pci=nomsi loop.max_part=15')