reMarkable 2 Recovery / Unbricking

Tools for recovery (works only under Linux)

Parts and prerequisites

To put the rM2 in recovery, you will need:

USB-C breakout board (you could probably use USB-C to Audio adapter and plug headpholnes to short B8)
Pogo pin adapter to usb the pogo pins are as follows, when viewed from the side, device facing up (VBUS is near the usb-c) GND,ID,D+,D-,VBUS
imx_usb_loader a binary is included, but feel free to compile it

run dmesg -w on your host to monitor
power off the device (hold the power button for 10 seconds)
connect the USB-C breakout board
pull down B8 (connect B8 over a 10K resistor to B12)
connect the pogo pins to the tablet and to the host usb Make sure the orientation is correct, you risk frying your device if you connect the pins in the wrong order
make sure the connection is good, use a short good, different cable, etc
if the device does not start on its own, press the Power Button. The screen should flash and say it's starting. After that, the screen should no longer update.
you should see a new device USB HID v1.10 Device [Freescale SemiConductor Inc SE Blank ULT1]
remove the pulldown resistor (disconnect B8)
run sudo ./imx_usb or add the udev rules to use it without sudo
should see USB Mass Storage device detected
should see a new mountable block device

to recover the ssh password, mount the home partition grep Developer <mountpoint>/root/.config/remarkable/xochitl.conf
to find a mountpoint run mount | grep home
TODO not tested, but something like dd if=raw of=/dev/mountedroot1

It is very important to use a pogo connector because it is almost impossible to achieve a stable connection in another way.
Only if the device is in recovery mode there will be messages in the dmesg output.
If you see messages like usb 1-1: device descriptor read/64, error -71, most likely it means that the device is in recovery mode and you have a poor connection to the pogo port.
B8 is on the bottom part of the USB port. So screen side is A and bottom side is B.
if not sure that device is powered off, try to connect the device to the charger, the screen should blink, disconnect it from the charger, hold the power button for at least 15 seconds.