This page is a rough guide on how to get linux running on the MK802II_A20 android hdmi stick.
I'm actually not sure how to call this device since it is sold on ali express under many names. I choose MK802II_A20 since that's the name of the uboot dram config that was closest to the actually config i'm using (see "Bootloader" below). Another good candidate for a name would be "QT800" since that is printed on the pcb (an there is a very similar hdmi dongle out there call "reko qt800")
The fist thing i needed is getting serial communication with the device working. I didn't know where and if the rs232 pins are exposed on the pcb. Also some of the promising looking test pads were pretty tiny. So i soldered cables to those test pads and hooked them up to an oscilloscope.