samsung-i9300: Kernel does not boot

Describe your issue

What's the expected behaviour?

Kernel boots.

What's the current behaviour?

Kernel does not boot. Device gets stuck in bootloader.

How to reproduce your issue?

Flash a recent kernel and try to boot. (or better yet, don't until someone has figured out why this happens)

What device are you using?

samsung-i9300, mainline kernel

Additional information

@grimler sent the following excerpt he acquired from the bootloader through serial debugging:

Starting kernel at 0x40008000...

SWITCH_SEL(1)

Which he said was the end of the log if I understood him right.

What's also worth noting is that I tried booting a newly built build of 5.11.8 which I know has worked in the past (it worked with a fresh rootfs right before I re-flashed the kernel with this new broken one) and it still wouldn't work.

There is the slim chance I was actually booting a new kernel, because I just reverted upgrade commits and set the pkgver to 9999 and booted — and built — the kernel, but I have no way of verifying that it actually booted the right one.

Possibly related: #1023 (closed)