This post is also on Medium.
Apparently, OnePlus was supposed to have really great support for custom roms. This I knew because when I got the OPO2 (OnePlus 2), there were a lot of great kernel developers working on it, like Franco.
Fast forward to this day and age and the device is a mess. Ages ago in a bid for stability, I had opted for the official (Chinese) Hydrogen OS roms, which were eventually frozen out at Marshmallow (Android v. 6.xx). Unsurprisingly, this meant that the phone was not performing well at all.
Trying to flash a custom recovery was a complete disaster. The only one which was willing to boot was v2.8.7.0, which was not able to install the latest LOS (v 15.xx, Android 8.xx).
Since the rant was getting long I will get back to that later. Right now the exact steps to get to the latest Android version (Pie, 9.xx** is simply as shown in the sections below.
NOTE: The key combination for booting into flashmode is VOL UP + Power.
For recovery it is VOL DOWN + Power
Also note that the above instructions for booting into flashmode and
recovery means hold both keys until the logo shows, then just hold the
appropriate VOL button. LET GO OF THE POWER BUTTON.
Grab the recovery set of fastboot files from this oneplus 2 thread.
Then either run the .bat file on Windows, or input each command into the
terminal if you're on a *nix device.
Very specifically, this means:
fastboot flash boot boot.img
fastboot flash system system.img
rem fastboot erase recovery
fastboot flash cache cache.img
fastboot flash modem NON-HLOS.bin
fastboot flash sbl1 sbl1.mbn
fastboot flash sdi sdi.mbn
fastboot flash pmic pmic.mbn
fastboot flash hyp hyp.mbn
fastboot flash bluetooth BTFM.bin
fastboot flash aboot emmc_appsboot.mbn
fastboot flash rpm rpm.mbn
fastboot flash tz tz.mbn
fastboot flash LOGO logo.bin
fastboot flash oem_stanvbk static_nvbk.bin
rem fastboot flash userdata userdata_64g.img
rem fastboot reboot
At this point your opo2 should boot, but not do much else. Now we will work our way through to getting a viable custom recovery since the oneplus default is terrible.
We will be using the official TWRP link along with a special cross bootloader compatible TWRP.
This means:
fastboot flash recovery twrp-2.8.7.0-oneplus2.img
fastboot boot twrp-2.8.7.0-oneplus2.img
Now we can get a more forward thinking (i.e, one with no trust zone errors) TWRP from here.
This needs to be copied into your device and flashed with the TWRP already installed in the previous step.
At this point we still can't actually install any custom roms, which is important since once that works everything else will fall into place. The remaining step is to grab a firware update (from Oxygen OS 3) which will work.
Specifically:
OOS_3.6.1_Firmware.zip) in the hybrid TWRP obtained before this.Finally, we can now move to CyanogenMod 13, which is the most stable custom ROM around. True, it has been depreciated (legacy continued by LineageOS) and is still based off Marshmallow (Android v. 6.xx) but it's a HUGE update.
Wherever gapps are mentioned, remember that this is an arm64 device.
cm-13.0-20161114-NIGHTLY-oneplus2.zipOptionally, even though most kernels are EOL (end-of-life) for this particular version (and the device in general), the Boeffla kernel is great.
Profit.
At this stage we can flash anything (almost). Let us get to the bleeding edge (Android 8.1, LineageOS 15.1) of stable OPO2 development one ROM at a time.
Pie (Android 9, LineageOS 16) does not really seem to be all too stable right now, so I will stop here. Additionally, the unified arctic kernel seems pretty good.