WIP: support for Ubiquiti EdgeRouter X (ER-X)

[srd424]

Not sure of etiquette here, but throught a draft PR might be useful to someone else (particularly in case I get distracted and don't get it finished!)

Have got this to tftpboot, haven't actually tested the networking yet but I'd be surprised if it didn't work. Haven't investigated writing to flash yet, and may well have some parameters / addresses set wrong so don't attempt it without a thorough review! Both factory firmware and openwrt use ubifs on this device so I'm assuming that will make things easier when I get around to it.

Doubtless needs tidying up, and things like useless wireless firmware removing too. Obviously I will squash when I'm happy with it.

[telent]

Nice!

[telent]

I have had less than massive success asking people to keep their kconfig minimal, but I'm going to carry on asking anyway :-) You don't need to include options that are turned on by other options, and it makes it easier to see what;'s important and what's incidental if you leave out the ones that can be inferred

(I know this is early-stage, my comment is forward-looking)

[srd424]

I just nicked this from one of the other devices, but noted :) Any tips on figuring out what's required, or is it just an interative process of reading Kconfig docs and diffing the result?

[srd424]

Hmmm, liminix kernels which work fine when tftpbooted fail to load to when written to flash. Best guess is the built-in uboot decompresses it to a different address in that instance and it's running into something else? (See openwrt/openwrt#12208 (comment))

The OpenWRT kernels include their own 'lzma-loader' which I suspect is the key to solving this. @telent, might need your help figuring out to how build it, I don't think my nix skills are likely to be up to it!