Adding Kobo Touch N905 (kobo-n905-imx507)

Created by: xy2iii

I'm opening this as a stub issue until a PR gets going.

There are two motherboards revisions of the N905. The main difference between the two is a different processor, as well as the presence of an SD card to replace eMMC. I am speaking on the later model, the one with an SD card slot, an imx507 (read the processor notes for this), and gold-ish contours in the middle of the motherboard.. As all data is stored on an SD, this makes it very easy to recover from what would be a brick on a phone (wrong flashing/does not boot).

Why?

This device can be bought for about 35$ online, it's very cheap, has open-sourced kernel, no binary blobs needed for core functionality (WiFi is blobbed, not much else) and is e-ink, which means it can last well weeks powered on because the e-ink screen uses no battery. It is so good that people actually use the Kobo as a flight computer! (There's an entire forum dedicated to this.)

Kernel, u-boot, etc sources

https://github.com/kobolabs/Kobo-Reader/tree/master/hw/imx508

Interesting notes

The Kobo software (which I'll refer as 'nickel' from now on) is self-contained within the internal SD card. In theory, this means that you can keep nickel on the internal SD card while installing pmOS on the external one, and choosing at boot via u-boot which to choose. In practice, this has been done. Interestingly, the functionality to boot from an SD card is already included in the native u-boot, all we need is a boot option to trigger it. This work has already been done and can be modified easily if needed.

UART

https://petit-noise.net/blog/kobo-touch-%E3%81%ABusb%E3%82%B7%E3%83%AA%E3%82%A2%E3%83%AB%E3%82%92%E7%B9%8B%E3%81%92%E3%82%8B/ Warning: RX and TX are swapped!!! I failed my soldering because of this.. After this, kobo will output dmesg on serial console, with baud rate 115200.