What else is considered a Sysupgrade Compatible Image?

Hello all. A quick question, just what qualifies as a "sysupgrade-compatible image" and is there a way to test whether a certain .bin file I have is or isn't sysupgrade compatible?

I ask because I installed LEDE on my old Linksys E4200 v1 and realized that it does not allow 802.11n, only (b/g) is available. I'd like to switch to Advanced Tomato (which is a based on Tomato Shibby), but am unsure if its .bin file is sysupgrade-compatible image.

Barring being able to move directly from LEDE to Advanced Tomato, can I revert back to the original firmware from Linksys using the webgui? I'm currently on the following LEDE version:

LEDE Reboot 17.01.0 r3205-59508e3 / LuCI lede-17.01 branch (git-17.051.53299-a100738)

Sysupgrade only applies when you flash from an existing OpenWrt or LEDE installation, to a newer LEDE or OpenWrt version.

If our wiki does not have any instructions for your device on how to revert to stock, the OpenWrt wiki might.

Thank you. I was able to use the generic "Back to Original Firmware" steps from their wiki.

Just to clarify: sysupgrade -n cannot be used to rollback to, say, OpenWRT CC?
I have managed this from OpenWRT DD to CC before.

For most routers the rollback to ancient Openwrt CC should work quite ok with sysupgrade -n

There are a few exceptions where e.g. the image format has changed so much that LEDE sysupgrade dislikes the CC image, but those are rare.

Thanks for the quick reply.

I asked after getting this:

root@Buffalo:/tmp# sysupgrade --test openwrt-lantiq-xway-WBMR-squashfs.image Image metadata not found Use sysupgrade -F to override this check when downgrading or flashing to vendor firmware Image check 'fwtool_check_image' failed.

I assume this is what you were referring to with sysupgrade not accepting an image.
CC may be ancient but it works whereas DD and LEDE don't.

Yes. I was referring to just that. I am not familiar with that device family, but e.g. mvebu devices need -F override to downgrade.