realtek: add support for Panasonic Switch-M48eG PN28480K

realtek: add support for Panasonic Switch-M48eG PN28480K

Panasonic Switch-M48eG PN28480K is a 48 + 4 port gigabit switch, based on
RTL8393M.

Specification:

- SoC           : Realtek RTL8393M
- RAM           : DDR3 128 MiB (Winbond W631GG8KB-15)
- Flash         : SPI-NOR 32 MiB (Macronix MX25L25635FMI-10G)
- Ethernet      : 10/100/1000 Mbps x48 + 2
  - port  1-40  : TP, RTL8218B x5
  - port 41-48  : RTL8218FB
    - port 41-44: TP
    - port 45-48: TP/SFP (Combo)
- LEDs/Keys     : 7x / 1x
- UART          : RS-232 port on the front panel (connector: RJ-45)
  - 3:TX, 4:GND, 5:GND, 6:RX (pin number: RJ-45)
  - 9600n8
- Power         : 100-240 VAC, 50/60 Hz, 0.5 A
  - Plug        : IEC 60320-C13
- Stock OS      : VxWorks based

Flash instruction using initramfs image:

1.  Prepare the TFTP server with the IP address 192.168.1.111
2.  Rename the OpenWrt initramfs image to "0101A8C0.img" and place it to
    the TFTP directory
3.  Download the official upgrading firmware (ex: pn28480k_v30000.rom)
    and place it to the TFTP directory
4.  Boot M48eG and interrupt the U-Boot with Ctrl + C keys
5.  Execute the following commands and boot with the OpenWrt initramfs
    image

    rtk network on
    tftpboot 0x81000000
    bootm

6.  Backup mtdblock files to the computer by scp or anything and reboot
7.  Interrupt the U-Boot and execute the following commands to re-create
    filesystem in the flash

    ffsmount c:/
    ffsfmt c:/

    this step takes a long time, about ~ 4 mins

8.  Execute the following commands to put the official images to the
    filesystem

    updatert <official image>

    example:

      updatert pn28480k_v30000.rom

    this step takes about ~ 40 secs

9.  Set the environment variables of the U-Boot by the following commands

    setenv loadaddr 0xb4e00000
    setenv bootcmd 'sleep 10; bootm;'
    saveenv

    'sleep 10;' is required as dummy to execute 'bootm' command correctly

10: Download the OpenWrt initramfs image and boot with it

    tftpboot 0x81000000 0101A8C0.img
    bootm

11: On the initramfs image, download the sysupgrade image and perform
    sysupgrade with it

    sysupgrade <imagename>

12: Wait ~ 120 seconds to complete flashing

Known Issues:

- 4x SFP ports are provided as combo ports by the RTL8218FB chip, but the
  phy driver has no support for it. Currently, only TP ports work by the
  RTL8218B support.

Note:

- "Switch-M48eG" is a model name, and "PN28480K" is a model number.
  Switch-M48eG has an another (old) model number ("PN28480"), it's not a
  Realtek based hardware.

- Switch-M48eG has a "POWER" LED (Green), but it's not connected to any
  GPIO pin.

- U-Boot checks the runtime images in the flash when booting and fails
  to execute "bootcmd" variable if the images are not existing.

- A filesystem is formed in the flash (0x100000-0x1DFFFFF) on the stock
  firmware and it includes the stock images, configuration files and
  checksum files. It's unknown format, can't be managed on the OpenWrt.
  To get the enough space for OpenWrt, move the filesystem to the head
  of "fs_reserved" partition by execution of "ffsfmt" and "updatert".

- A GPIO pin on PCA9539 is used for resetting external RTL8218B phys and
  RTL8218FB phy.
  This should be specified as "reset-gpios" property in MDIO node, but
  the current configuration of RTL8218B phy in the driver seems to be
  incomplete and RTL8218FB won't be configured on RTL8218D support.
  So, ethernet ports on these phys will be broken after hard-resetting.
  At the moment, configure this pin as gpio-hog to avoid breaking by
  resetting.

- This model has 2x Microchip TCN75A thermal sensors. Linux Kernel
  supports TCN75 chip on lm75 driver, but no support for TCN75'A'
  variant.
  At the moment, use TCN75 support for the chips instead.

Back to the stock firmware:

1. Delete "loadaddr" variable and set "bootcmd" to the original value

   on U-Boot:

     setenv loadaddr
     setenv bootcmd 'ffsrdm c:/runtime.had 0x81000000;alphadec c:/runtime.had 0x81000240 0x80010000;'

   on OpenWrt:

     fw_setenv loadaddr
     fw_setenv bootcmd 'ffsrdm c:/runtime.had 0x81000000;alphadec c:/runtime.had 0x81000240 0x80010000;'

2. Perform reset or reboot

  on U-Boot:

    reset

  on OpenWrt:

    reboot

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>