I'm running Debian powerpc/ppc64 on a couple of PowerPC machines (PowerMac6,7 and PowerMac11,2) and the GRUB installation seems to be working perfectly, huge kudos to everyone involved!
So, apart from the big one in $SUBJECT (Linux 5.6.11 seems fine; I'm running a custom kernel, let me know if you want the .config), here are some minor issues I noticed:
Plymouth colours look wrong (only tested on the 6,7, the 11,2 is headless atm), probably a framebuffer endiannes issue?
According to the datasheets I found (which could be wrong, of course), the G4 7447A should also have a thermal assist unit (TAU), but the flag isn't enabled for this model. Could it be an oversight? (I could probably check if it exists/works and whip up a kernel patch accordingly.)
Also, what's happening with the HIGHMEM on PowerPC? My 6,7 has 1,5 GiB of RAM and the LOWMEM split is at 768 MiB, which seems extremely low, compared to x86 machines (I personally wasn't expecting to need HIGHMEM at all, but maybe the the address space is really that limited, I don't know.)
Best regards,
Rui