@Inglebard said in Device compatibility/lifespan with UT:
why is it not always possible to update the kernel?
To start with your last question. It is not always possible to update the kernel because the proprietary drivers that make the hardware of the device work are compiled against a specific version of the kernel. If a newer version is used, then the drivers may stop working, and they cannot be fixed to work with the newer kernel because the source code for them is not available.
The changes needed to work with Ubuntu 20.04 could in principle be backported to older kernels by someone wanting the see these older devices keep running on later versions of Ubuntu Touch. But that is a huge amount of work in itself, and also just one step in getting some of these devices up to date.
I would like to know what makes a phone compatible with Ubuntu Touch?
The short answer is: Anyone willing to put in the work to make a port of Ubuntu Touch for that phone.
A longer answer would be: If the phone has at least 3 GB of RAM, runs on a relatively new Kernel with sources published, and there is a working Halium version available for the Android version it shipped with, that would make it a good candidate for porting.
I would also like to know how to determine if a device that is compatible with 16.04 or 20.04 will be compatible with 22.04 or 24.04, or even beyond (What is its lifespan)?
This depends on the changes that are introduced in the underlying Ubuntu version that is being targeted. For instance 20.04 no longer supported Upstart as the init system. Everything was moved to SystemD (this had happened earlier, but those versions were skipped as UT targets). This in turn meant that only kernels that could support all the SystemD features that were required in Ubuntu 20.04 to get Ubuntu Touch running, could be supported. Sometimes these features could be backported to older kernels (as is ongoing for the OnePlus One) but since different devices used different kernel versions, this work would most likely need to be re-done for each device for which support was desired.
It is not always clear before starting to work on it, what changes in the new version of Ubuntu will have what impact on Ubuntu Touch. And which changes will cause the most work to adapt to. That is why it is difficult to state beforehand how long any particular device will be able to be supported. You can assume though that once a device gets support for an new version of Ubuntu Touch, you will be able to receive security updates for that device for at least as long as the underlying version of Ubuntu is supported by Canonical. Feature updates might stop earlier due to the need to keep somewhat up to date with the current versions of Ubuntu to benefit the most from the latest improvements to the software components being used in the OS.
Last but not least, the commitment of the porter to the device determines to a very great extent how long and how good support will be for any given device.
Some ports are sponsored by, or done in collaboration with, device sellers, such as Hallo Welt with their Volla Phones, and Fairphone with the FP4. These have a better chance of seeing good support.