[Shield Android TV General] Downunder35m:
Already this 7.2 update is creating topics all over the place :(

Anyway, let me try to at least some light on things.

My latest findings:

1. The bootloader does not downgrade to 7.1 once you had at least the 7.2.x installed, not sure about 7.2 as it is too late for me to test this.

I did not check with the 6.3 either but maybe someone who did is able to state what bootloader is working then.

2. The DTB is not included in the firmware images at all but it seems it was included in some pre 7.1 to include the "updates" for the Darcy models.

What makes the Zulu one tick is the simple fact that it is patched to disable DM-Verity completely.

Hence the requirement for the fastboot -w or a factory reset.

TWRP and such....

This might get quite long, so anyone without half decent knowledge about rooting, firmwares and recoveries can just skip it ;)

First thing I learned from 7.2 was: Do not mess with your bootloader!!!

Second thing I learned is that Linus was right with his statement about NVidia and their open source suppport.

So what actually changed?

For starters the NVidia statement of the developer firmware being rootable is not true the same way it was before.

Google latest kernel fixes and changes have been implemented - look it up yourself please to spare me thausand of lines of typing!

In short it means that all backdoors or such that Magisk or SU have used are unavailabe now.

Rooting still works but with the limit of write access.

And that is the important factor one for TWRP, the second is "routing".

Let me try to word it as simple as I can...

We can not modify the system to ignore the stock recovery or related security features.

We can not write to required areas of the system required to boot into TWRP through the recovery.

If you somehow manage to get into TWRP, like when I still had a working mod, there again is no write access to system available and the internal memory will be corrupted if you write a backup.

The DTB Zulu provided gives us system wide write rights again by disabling DM-Verity but this only goes for the system!!

The recovery does not use the DTB in this way.

Best thing you end up with is a dark screen where ADB seems to be working.

It actually works with full root access for me in several cases LOL

So if that really is TWRP then why can't we see it?

My TV is great as it allows multi input formats.

So a 1080P signal will be accepted as such.

And every time this screen format changes I see a little pop up with the new resolutions on the screen.

Since 7.2 this popup no longer shows up....

TWRP might actually be there and working but we can not see or use it.

The strange thing however is that at least on the 7.2.2 I had the strange problem that just trying to boot into tWRP through fastboot resulted in a corrupt system.

The bootloader realises the recovery written into the temp area has no NVidia signature or hash code to match.

This means for the bootloader a possible attack on the system happened and it is "secured", resulting in a soft brick.

My plans to fix all this crap for good:

The DTB is a partial solution at best as we

a) don't really know how compatible it is with future updates.

b) we still fail to properly use TWRP again.

All up a total nighmare for any modder or person with a lot of data and apps to backup and restore.

My first attempt was to build the 7.2 from the sources, thinking at least here the NVidia statements are correct that their installer takes care of everything.

Lol! It did take of about 120GB in downloads but did not give me any of require software suites actually required to even load a build tree.

Would need far more time than I have to mae complete and work with registrations, accounts and all this.

So I decided to go back to my roots before Magisk was a thing.

Dissecting the firmware, disabling all new "safety" features and not required encryptions and hash checks.

That bit I think I finnished to my satisfaction.

On the packing to make it work to be installed under 7.2.X I am still working.

Biggest drawback for me is that I lost TWRP and that the TWRP builder does not even let me log in on my Shield.

So even if a more offical way or porting or building could be a way out I can not access it.

Means I can neither try to install my modded firmware nor test it.

So if anyone reading here has a confirmed way to downgrade to something that brings TWRP back to live with working write access and working backup functions:

Don't be shy, we don''t bite (much)!

Share your way, give us the links and if my magic still works a bit this nightmare shall soon be over for good :)