A couple of updates that may be useful for anyone else working on this:
Serial, AR750S is "Deaf"
Two of the eBay-sourced “FTDI” adapters that I have used in the past with a variety of devices seem unable to drive the RX pin of the AR750S sufficiently or properly to send data to the device over serial. The serial pins appear to be 2.5 V logic. Using an Adafruit FTDI Friend resolved the issue.
Uploading Combined UBI Image Through U-Boot
The factory U-Boot doesn’t like post of
*-factory.ubi, failing with
## Error: input file format error!
## Error: couldn't find start of data in next packet!
Creating a symlink to, for example,
factory.bin allows use of
curl -v -F 'email@example.com' http://192.168.1.1/index.html
to upload NAND-based firmware (with the current GL.iNet U-Boot image).
No, it’s not booting completely yet and am working through challenges in getting the NAND driver to load. Edit: This may be due to there not being a NAND driver for the ath79 architecture. Looking into that now.
[ 0.299727] ath79-spi 1f000000.spi: cs1 >= max 1
[ 0.304503] spi_master spi0: spi_device register error /ahb/spi@1f000000/flash@1
[ 0.312184] spi_master spi0: Failed to create SPI device for /ahb/spi@1f000000/flash@1
There are no NAND drivers for ath79 that are acceptable for upstream Linux or OpenWrt and it is exceptionally unlikely that there will be prior to Kernel 4.19 being adopted for ath79.
See, for example https://github.com/openwrt/openwrt/pull/1428
To be clear, OpenWrt NOR-based targets should be functional, when they are available.