Trekstore Surftab Wintron 7.0 III: Linux

See post about hardware: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-hardware.html
See post about UEFI: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-uefi.html
See post about Linux: https://technikgebastel.blogspot.de/2016/04/trekstore-surftab-wintron-70-iii-linux.html

Current status:

What works (tested):
- booting Debian or Ubuntu with XFCE4, i3, Gnome3
- display: brightness change, screen rotation, video playback
- touchscreen (GSL1686): calibration, multitouch input (including multitouch gestures in Gnome3)
- Wireless (rtl8723bs)
- USB-OTG
- micro-SD card slot
- battery charge state (AXP288)

- orientation sensor (bma22e with BMA2x2)

What probably works (not tested):
- Bluetooth (rtl8723bs)

What does not yet work:
- audio output (ALC5651 not supported with linux kernel 4.3, included starting 4.5, but wlan-patches for 4.5 cause problems)
- cameras (gc0310, ov2680)

What will probably never work, aka no idea how to make it work:
- hardware buttons (except power button)

Once everything except stuff in the category "What will probably never work, aka no idea how to make it work:" is working, I will document everything here.

Trekstore Surftab Wintron 7.0 I: Hardware

See post about hardware: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-hardware.html
See post about UEFI: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-uefi.html
See post about Linux: https://technikgebastel.blogspot.de/2016/04/trekstore-surftab-wintron-70-iii-linux.html

Recently a colleague of mine made me aware of a very cheap 7 inch Windows 10 tablet. Even though he intended to use it with Windows 10, when searching for the specs I came across some forum posts of people that tried to run Ubuntu instead of Windows on it.
The Trekstore Surftab Wintron 7 (http://www.trekstor.de/detail-surftabs-de/product/produktsupport/product/surftab-wintron-70-v2.html) costs about 50 Euro.
Motivated by Ron and Frank Riegers talk about the 32C3 (https://www.youtube.com/watch?v=DBv0eykj_m8&feature=youtu.be&t=1h5m35s) I started to tackle the problem of getting Debian to run on this device.

The inside looks like:

Specifications:
Display: 7 inch, 1024x600, IPS
CPU: Intel Atom Z3735G (http://ark.intel.com/de/products/80275/Intel-Atom-Processor-Z3735G-2M-Cache-up-to-1_83-GHz)

PMIC: AXP288 (http://www.x-powers.com/product/AXP288_en.php)

RAM: 1 GB DDR3, Kingston N11915-01, D2516EC4BXGGB (http://media.kingston.com/pdfs/emmc/MKF_585_DDR3_3L_US.pdf)

CMOS Flash memory: 64 Mbit 25LQ64GVIG

internal memory: 16 GB, FORESEE NCEMBS99-16GB

cameras: front 0.3 MP, back 2 MP

Audio: ALC5651, internal speaker (mono), 3,5mm external connector

Wireless/Bluetooth: RTL8723BS, 802.11 b/g/n, 2.4 GHz

Touchscreen: 5 fingers, Silead GSL1686

battery: 2500 mAh, 3.7V

microSD: SDHC, SDXC

microUSB: host and client mode

orientation sensor BMA222E (BMA2x2)

cameras: Gcoreinc gc0310, OmniVision 2680