bcm53xx: add Cisco Meraki MR32

bcm53xx: add Cisco Meraki MR32

This patch adds support for Cisco Meraki MR32.
The unit was donated by Chris Blake. Thank you!

WARNING:
Only the 1x1:1 abgn Air Marshal WIPS wifi is currently supported by b43:
 b43-phy2: Found PHY: Analog 9, Type 4 (N), Revision 16
 b43-phy2: Found Radio: Manuf 0x17F, ID 0x2057, Revision 9, Version 1
 b43-phy2: Loading firmware version 784.2 (2012-08-15 21:35:19)
 and only as 802.11ABG!

while WIFI1 and WIFI2 (both BCM4352) are not:
 b43-phy0: Broadcom 4352 WLAN found (core revision 42)
 b43-phy0 ERROR: FOUND UNSUPPORTED PHY (Analog 12, Type 11 (AC), Revision 1)

Hardware Highlights:

SoC:	Broadcom BCM53016A1 (1 GHz, 2 cores)
RAM:	128 MiB
NAND:	128 MiB Spansion S34ML01G2 (~114 MiB useable)
ETH:	1GBit Ethernet Port - PoE
WIFI1:	Broadcom BCM43520 an+ac (2x2:2 - id: 0x4352)
WIFI2:	Broadcom BCM43520 bgn (2x2:2 - id: 0x4352)
WIFI3:	Broadcom BCM43428 abgn (1x1:1 - id: 43428)

BLE:	Broadcom BCM20732 (ttyS1)
LEDS:   1 x Programmable RGB Status LED (driven by a PWM)
	1 x White LED (GPIO)
	1 x Orange LED Fault Indicator (GPIO)
	2 x LAN Activity / Speed LEDs (On the RJ45 Port)
BUTTON: one Reset button
MISC:   AT24C64 8KiB EEPROM (i2c - stores Ethernet MAC + Serial#!)
	ina219 hardware monitor (i2c)
	Kensington Lock

SERIAL:
	WARNING: The serial port needs a TTL/RS-232 3V3 level converter!
	The Serial setting is 115200-8-N-1. The board has a populated
	right angle 1x4 0.1" pinheader.
	The pinout is: VCC, RX, TX, GND. (Use a multimeter)

Flashing needs a serial adaptor (due to the lack of a working dropbear on
the original firmware).

This flashing procedure for the MR32 was tested with firmware:
"r23-149867:150252-aacharya".

0. Create a seperate Ethernet LAN which does not have access to the internet.
   Ideally use 192.168.1.2 for your PC. Make sure to reserve 192.168.1.1 it
   will be used later on by the OpenWrt firmware. The original Meraki firmware
   will likely try to setup the network via DHCP Discovery, so make sure your
   PC is running a DHCP-Server (i.e.: dnsmasq)
   '# dnsmasq -i eth# -F 192.168.1.5,192.168.1.50
   Furthermore, the PC needs a supported ssh/http/ftp server in order to
   retrieve the initramfs + dtb file

1. Disassemble the MR32 device by removing all screws (4 screws are located
   under the 4 rubber feets!) and prying open the plastic covers without
   breaking the plastic retention clips. Once inside, remove all the screws
   on the outer metal shielding to get to the PCB. It's not necessary to
   remove the antennas!

2. Connect the serial cable to the serial header.

3. Partially reassemble the outer metal shielding to ensure that the SoC
   has a proper heat sink.

4. Connect the Ethernet patch cable to the device and the power cable.

5. Wait for the device to boot and enter the root shell.
   (rooting is not discussed in detail here please refer to
   Chris Blake - "pwning the meraki mr18" blog post:
   <https://servernetworktech.com/2016/02/pwning-the-meraki-mr18/>
   (The same method works with the MR32's r23-149867:150252-aacharya)

   Wait for the MR32 to enter the "<Meraki>" prompt and enter:
   <Meraki> odm serial_num read
   (Verify that it matches what's on the S/N Sticker on the back!)
   <Meraki> odm serial_num write Q2XX-XXXX-XXXV
   <Meraki> odm serial_num read
   (Verify that the S/N has changed - and the LED start to flash)

   now to flash the firmware:
   <Meraki> odm firmware part.safe "http://192.168.1.2/mr32-initramfs.bin"

Once OpenWrt booted use sysupgrade to permanently install
OpenWrt. To do this: Download the latest sysupgrade.bin file
for the MR32 to the device and use sysupgrade *sysupgrade.bin
to install it.

WARNING: DO NOT DELETE the "storage" ubi volume!

To flash later MR32 Firmwares like r25-201804051805-G885d6d78-dhow-rel
requires in-circut-i2c tools to access the I2C EEPROM AT24C64 next to
the SoC. The idea is pretty much the same as from Step 5 from above:
Change the serial number to Q2XXXXXXXXXV (should be around 0x7c), then
attach a serial cable, ethernet (but make sure the device can't reach
the internet!) hit "s" (the small s!) during boot to enter the root-shell
and add the following commands to the /storage/config there:

serial_allow_odm true
serial_access_enabled true
serial_access_check false
valid_config true

and then hit exit to let it finish booting.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>