realtek: add support for Zyxel XS1930-12HP

realtek: add support for Zyxel XS1930-12HP

Add support for RTL9313-based Zyxel XS1930-12HP, a 12-port Multi-Gig
switch with 10x 100M/1G/2.5G/5G/10G RJ45 and 2x 1G/10G SFP+ ports.

Hardware
========

  - RTL9313 SoC
  - 256MiB DDR3 RAM (Winbond W632GU6MB)
  - 32MiB SPI-NOR Flash (Macronix MX25L25645G)
  - 8x 100M/1G/2.5G/5G/10G RJ45 (Aquantia AQR813)
  - 2x 100M/1G/2.5G/5G/10G RJ45 (2x Aquantia AQR113C)
  - 2x 1G/10G SFP+
  - PoE:
    - Ports 1-8 with PoE++/802.3bt
    - 2x RTL8239 + GigaDevice FD32F103 MCU
  - RTL8231 for port LEDs
  - LM96000 I2C hardware monitor
  - 3-pin fans
  - Front LEDs: PWR, SYS, CLOUD, LOCATOR, POE USAGE
  - Console: TTL 3.3V, 115200 8N1
  - Software chain:
    - Bootbase/stripped-down U-Boot
    - BootExt
    - RAS/ZyNOS

Console
=======

The console port is a 4-pin header reachable without opening case.
Looking at the front port-side of the device, turn the device 90 degrees
clockwise. On this side, there's a rectangular opening in the honeycomb
structure. Pinout is (from left/front to right/back): GND RX TX VCC

Hardware quirks
===============

* The SFP signals RX_LOS, MOD_ABS and TX_FAULT do not have dedicated GPIO
  lines each. Instead, there's a multiplexer (using GPIO12 and GPIO14)
  which - depending on its state - connect this single GPIO line to RX_LOS,
  MOD_ABS or TX_FAULT (GPIO19 for SFP1, GPIO27 for SFP2). This requires
  a special adapter driver (which is backed by a gpio-mux) that makes
  this hardware design and Linux' SFP core work together.

* SFP slots are disabled by default. GPIO6 and GPIO7 seems to be gates
  for SFP1 and SFP2 respectively. The need to be pulled low to make SFP
  modules work (i.e. respond to I2C requests and pass GPIO signals).

* Fan can only be set to SLOW or FAST mode, no real speed/PWM control.

Disclaimer
==========

PoE not yet supported.

Flashing OpenWrt will overwrite BootExtension + ZyNOS. BootExtension
functionality (e.g. initramfs boot as mentioned below) is not available
anymore then. The U-boot/Bootbase still has some limited functionality
which can be used in emergency cases.

Installation
============

Simple web upgrade:

1. Take the OpenWrt factory.bin image generated by the build.

2. In the ZyNOS web UI, login and go to Maintenance -> Firmware Upgrade.

3. Under "Boot Image", make sure the Config Boot Image is set to 1. In
   other words, make sure the switch booted from firmware image 1 or it
   will do so on next reboot.
   This is crucial, otherwise OpenWrt cannot boot.

4. Below, select and upload the factory.bin image. After clicking
   upgrade, the image will be flashed.

5. After flashing has finished, reboot the switch. It will now boot into
   OpenWrt.

Initramfs boot
==============

NOTE: You need to use Xmodem transfer, the bootloader doesn't support
      Ymodem nor any networking.
      This only works as long as the default ZyNOS firmware is
      installed.

1. Connect to the switch using serial and interrupt the boot process
   to enter debug/recovery mode.

2. You need to unlock the bootloader. Use known methods [1] and [2] to
   obtain the unlock code and unlock the bootloader with:

   > ATEN 1,<unlock_code>

3. Upload the initramfs image using Xmodem:

   > ATUP <address>,<file_length>

   <address>: you may use any RAM address >= 0x80300000
   <file_length>: length of image in bytes

4. After the transfer has finished, boot the image with:

   > ATGO <address>

5. Wait for OpenWrt to boot. At this stage, it might be wise to create a
   backup/dump of the Flash partitions.

Return to stock firmware
========================

1. Download the firmware for the switch from Zyxel website.

2. Unzip the download, there should be a .bin file with a alphanumeric
   name.

3. Upload this file to running OpenWrt.

4. Run (use -F since the image doesn't have image metadata):

   > sysupgrade -F <stock-firmware>.bin

5. Wait for the sysupgrade to succeed and the switch reboot. At the next
   boot, ZyNOS should come up again.

Recovery
========

The Bootbase loader is actually a modified U-Boot variant. You can enter
it by spamming $ during the DRAM test.

The U-Boot shell can be unlocked with [1] and [2]. Note that the command
is slightly different, using a space instead of a comma, and lowercase:

> aten 1 <unlock_code>

You should now have more-or-less a standard RTK-U-boot shell from where
you can upload and write a new image to flash. Use e.g.:

> upgradeY image2 81000000 115200

Wait for the upgrade process to finish and reboot the switch.

===
[1] https://akao.co.uk/tools/zyxel_unlocker/
[2] https://www.ixo.de/info/zyxel_uclinux/

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22909
Signed-off-by: Robert Marko <robimarko@gmail.com>