I got so pissed off at the Honor 6x that I had to take a break from trying to fix it.
It turns out that the way to enter fastboot is to hold Vol. Down during startup AND have it plugged in. It's really strange, given that most other phones just need the former.
Recovery's so crippled that there isn't an option to flash updates from SD card. I know this is the same company that refuses to let you unlock your bootloader, but still, what were they thinking?
This thing is capable of ADB in recovery, but:
C:\Users\[USERNAME]>adb devices
List of devices attached
[SERIAL NUMBER] unauthorized
Hence:
C:\Users\[USERNAME]>adb reboot fastboot
error: device unauthorized.
This adbd's $ADB_VENDOR_KEYS is not set; try 'adb kill-server' if that seems wrong.
Otherwise check for a confirmation dialog on your device.
I'd have to enable USB debugging, but that needs me to boot into the system normally, which I can't do.
Try something like--
fastboot getvar all
for example, to test if the connection is hot.
I entered fastboot, and I got this:
C:\Users\[USERNAME]>fastboot getvar all
getvar:all FAILED (remote: Command not allowed)
finished. total time: -0.000s
Not too exciting, but I guess it works?
Also, on the topic of flashing the stock ROM from the SD card, I haven't had any luck doing that. Not even something resembling a step in the right direction.
As far as I know, I'm SOL. Maybe there's some way to flash the stock ROM directly through fastboot, rather than using some proprietary software? That, or I should cut my losses and tell him to take it to a service center.