realtek: rtl931x: Add support for Plasma Cloud ESX28 Switch

realtek: rtl931x: Add support for Plasma Cloud ESX28 Switch

The Plasma Cloud ESX28 Switch is a 24 + 4 port multi-GBit switch with
24x 10/100/1000/2500BaseT Ethernet ports and 4x SFP+ module slot.

Hardware:

- RTL9312C SoC
- Macronix MX25L25645G (32MB flash)
- 512MB DDR3 SDRAM
- RTL8231 GPIO extender to control the port LEDs
- 6x RTL8224 4x 10m/100m/1/2.5 Gigabit PHY
- SFP+ 4x 10GBit slot

The switch is powered directly via AC.

The external RS232 serial connector (RJ45, Cisco pinout) can be used to
access the terminal. Serial connection is via 115200 baud, 8N1.

A reset button is accessible through a hole in the front panel.

Installation
------------

* The device can be flashed by using sysupgrade command. Either from the
  original vendor firmware or using an initramfs (see "Debug")
* Connect serial on front panel. Connection parameters: 115200 8N1
* The image must be copied using scp to /tmp of the device

      scp openwrt-realtek-rtl931x-plasmacloud_esx28-squashfs-sysupgrade.bin root@[IP address of the device]:/tmp/

* start sysupgrade without saving the original vendor configuration

      sysupgrade -n /tmp/openwrt-realtek-rtl931x-plasmacloud_esx28-squashfs-sysupgrade.bin

Installation via u-boot
-----------------------

If you have an TFTP server connected to the switch, it is possible to
directly install the device using the factory image from u-boot

    # setup networking and IP of TFP server
    rtk network on
    setenv ipaddr 10.100.100.99
    setenv serverip 10.100.100.20

    # get factory image
    tftp 0x84000000 factory.bin

    # erase firmware partitions
    sf probe 0
    sf erase 0x5e0000 0x1a20000

    # write firmware to both partitions
    sf write ${fileaddr} 0x5e0000 ${filesize}
    sf write ${fileaddr} 0x12f0000 ${filesize}

    # adjust the boot commands
    setenv bootargs "mtdparts=spi0.0:768k(u-boot),64k(u-boot-env),64k(u-boot-env2),5120k(reserved),13376k(inactive),13376k(firmware2)"
    setenv bootcmd "rtk init; bootm 0xb52f0000"

    # restart
    reset

Debug
-----

* Connect serial on front panel. Connection parameters: 115200 8N1.
* A tftp server is required, tftpd-hpa works well.
* Power the device, at U-Boot start rapidly hit Esc key to stop autoboot
* Enter passwords: "1234" or "plasmapsx"
* Enable network:

      rtk network on

* Change ip address of device:

      setenv ipaddr 192.168.1.6

* Download initramfs from TFTP server:

      tftpboot 0x84000000 192.168.1.111:openwrt-realtek-rtl931x-plasmacloud_esx28-initramfs-kernel.bin

* Boot loaded file:

      bootm 0x84000000

Signed-off-by: Harshal Gohel <hg@simonwunderlich.de>
Co-developed-by: Sven Eckelmann <se@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <se@simonwunderlich.de>
Link: https://github.com/openwrt/openwrt/pull/20172
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>