ipq40xx: add support for the ZyXEL NBG6617

ipq40xx: add support for the ZyXEL NBG6617

This patch adds support for ZyXEL NBG6617

Hardware highlights:

SOC:    IPQ4018 / QCA Dakota
CPU:    Quad-Core ARMv7 Processor rev 5 (v7l) Cortex-A7
DRAM:   256 MiB DDR3L-1600/1866 Nanya NT5CC128M16IP-DI @ 537 MHz
NOR:    32 MiB Macronix MX25L25635F
ETH:    Qualcomm Atheros QCA8075 Gigabit Switch (4 x LAN, 1 x WAN)
USB:    1 x 3.0 (via Synopsys DesignWare DWC3 controller in the SoC)
WLAN1:  Qualcomm Atheros QCA4018 2.4GHz 802.11bgn 2:2x2
WLAN2:  Qualcomm Atheros QCA4018 5GHz 802.11a/n/ac 2:2x2
INPUT:  RESET Button, WIFI/Rfkill Togglebutton, WPS Button
LEDS:   Power, WAN, LAN 1-4, WLAN 2.4GHz, WLAN 5GHz, USB, WPS

Serial:
	WARNING: The serial port needs a TTL/RS-232 3.3v level converter!
	The Serial setting is 115200-8-N-1. The 1x4 .1" header comes
	pre-soldered. Pinout:
	  1. 3v3 (Label printed on the PCB), 2. RX, 3. GND, 4. TX

first install / debricking / restore stock:
 0. Have a PC running a tftp-server @ 192.168.1.99/24
 1. connect the PC to any LAN-Ports
 2. put the openwrt...-factory.bin (or V1.00(ABCT.X).bin for stock) file
    into the tftp-server root directory and rename it to just "ras.bin".
 3. power-cycle the router and hold down the the WPS button (for 30sek)
 4. Wait (for a long time - the serial console provides some progress
    reports. The u-boot says it best: "Please be patient".
 5. Once the power LED starts to flashes slowly and the USB + WPS LEDs
    flashes fast at the same time. You have to reboot the device and
    it should then come right up.

Installation via Web-UI:
 0. Connect a PC to the powered-on router. It will assign your PC a
    IP-address via DHCP
 1. Access the Web-UI at 192.168.1.1 (Default Passwort: 1234)
 2. Go to the "Expert Mode"
 3. Under "Maintenance", select "Firmware-Upgrade"
 4. Upload the OpenWRT factory image
 5. Wait for the Device to finish.
    It will reboot into OpenWRT without any additional actions needed.

To open the ZyXEL NBG6617:
 0. remove the four rubber feet glued on the backside
 1. remove the four philips screws and pry open the top cover
    (by applying force between the plastic top housing from the
    backside/lan-port side)

Access the real u-boot shell:
ZyXEL uses a proprietary loader/shell on top of u-boot: "ZyXEL zloader v2.02"
When the device is starting up, the user can enter the the loader shell
by simply pressing a key within the 3 seconds once the following string
appears on the serial console:

|   Hit any key to stop autoboot:  3

The user is then dropped to a locked shell.

|NBG6617> HELP
|ATEN    x[,y]     set BootExtension Debug Flag (y=password)
|ATSE    x         show the seed of password generator
|ATSH              dump manufacturer related data in ROM
|ATRT    [x,y,z,u] RAM read/write test (x=level, y=start addr, z=end addr, u=iterations)
|ATGO              boot up whole system
|ATUR    x         upgrade RAS image (filename)
|NBG6617>

In order to escape/unlock a password challenge has to be passed.
Note: the value is dynamic! you have to calculate your own!

First use ATSE $MODELNAME (MODELNAME is the hostname in u-boot env)
to get the challange value/seed.

|NBG6617> ATSE NBG6617
|012345678901

This seed/value can be converted to the password with the help of this
bash script (Thanks to http://www.adslayuda.com/Zyxel650-9.html authors):

- tool.sh -
ror32() {
  echo $(( ($1 >> $2) | (($1 << (32 - $2) & (2**32-1)) ) ))
}
v="0x$1"
a="0x${v:2:6}"
b=$(( $a + 0x10F0A563))
c=$(( 0x${v:12:14} & 7 ))
p=$(( $(ror32 $b $c) ^ $a ))
printf "ATEN 1,%X\n" $p
- end of tool.sh -

|# bash ./tool.sh 012345678901
|
|ATEN 1,879C711

copy and paste the result into the shell to unlock zloader.

|NBG6617> ATEN 1,0046B0017430

If the entered code was correct the shell will change to
use the ATGU command to enter the real u-boot shell.

|NBG6617> ATGU
|NBG6617#

Co-authored-by: David Bauer <mail@david-bauer.net>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: David Bauer <mail@david-bauer.net>