ath79: add support for Huawei AP6010DN

ath79: add support for Huawei AP6010DN

Huawei AP6010DN is a dual-band, dual-radio 802.11a/b/g/n 2x2 MIMO
enterprise access point with one Gigabit Ethernet port and PoE
support.

Hardware highlights:
- CPU: AR9344 SoC at 480MHz
- RAM: 128MB DDR2
- Flash: 32MB SPI-NOR
- Wi-Fi 2.4GHz: AR9344-internal radio
- Wi-Fi 5GHz: AR9580 PCIe WLAN SoC
- Ethernet: 10/100/1000 Mbps Ethernet through Atheros AR8035 PHY
- PoE: yes
- Standalone 12V/2A power input
- Serial console externally available through RJ45 port
- External watchdog: CAT706SVI (1.6s timeout)

Serial console:
  9600n8 (9600 baud, no stop bits, no parity, 8 data bits)

MAC addresses:
  Each device has 32 consecutive MAC addresses allocated by
  the vendor, which don't overlap between devices.
  This was confirmed with multiple devices with consecutive
  serial numbers.
  The MAC address range starts with the address on the label.
  To be able to distinguish between the interfaces,
  the following MAC address scheme is used:
    - eth0 = label MAC
    - radio0 (Wi-Fi 2.4GHz) = label MAC + 1
    - radio1 (Wi-Fi 5GHz) = label MAC + 2

Installation:
0. Connect some sort of RJ45-to-USB adapter to "Console" port of the AP

1. Power up the AP

2. At prompt "Press f or F  to stop Auto-Boot in 3 seconds",
   do what they say.
   Log in with default admin password "admin@huawei.com".

3. Boot the OpenWrt initramfs from TFTP using the hidden script "run ramboot".
   Replace IP address as needed:

   > setenv serverip 192.168.1.10
   > setenv ipaddr 192.168.1.1
   > setenv rambootfile openwrt-ath79-generic-huawei_ap6010dn-initramfs-kernel.bin
   > saveenv
   > run ramboot

4. Optional but recommended as the factory firmware cannot be downloaded publicly:
   Back up contents of "firmware" partition using the web interface or ssh:

   $ ssh root@192.168.1.1 cat /dev/mtd11 > huawei_ap6010dn_fw_backup.bin

5. Run sysupgrade using sysupgrade image. OpenWrt
   shall boot from flash afterwards.

Return to factory firmware (using firmware upgrade package downloaded from non-public Huawei website):
1. Start a TFTP server in the directory where
   the firmware upgrade package is located

2. Boot to u-boot as described above

3. Install firmware upgrade package and format the config partitions:

   > update system FatAP6X10XN_SOMEVERSION.bin
   > format_fs

Return to factory firmware (from previously created backup):
1. Copy over the firmware partition backup to /tmp,
   for example using scp

2. Use sysupgrade with force to restore the backup:
   sysupgrade -F huawei_ap6010dn_fw_backup.bin

3. Boot AP to U-Boot as described above

Quirks and known issues:
- The stock firmware has a semi dual boot concept where the primary
kernel uses a squashfs as root partition and the secondary kernel uses
an initramfs. This dual boot concept is circumvented on purpose to gain
more flash space and since the stock firmware's flash layout isn't
compatible with mtdsplit.
- The external watchdog's timeout of 1.6s is very hard to satisfy
during bootup. This is why the GPIO15 pin connected to the watchdog input
is configured directly in the LZMA loader to output the AHB_CLK/2 signal
which keeps the watchdog happy until the wdt-gpio kernel driver takes
over. Because it would also take too long to read the whole kernel image
from flash, the uImage header only includes the loader which then reads
the kernel image from flash after GPIO15 is configured.

Signed-off-by: Marco von Rosenberg <marcovr@selfnet.de>
Link: https://github.com/openwrt/openwrt/pull/15941
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>