Sorry for the followup, but I did finally manage to track this down to a
firmware/driver incompatibility and bisected `linux-firmware` to find
when it broke.
Since the firmware is just binaries, I can't really tell ya what is
wrong, but this is the commit where writing to the sysfs interface (and
I was doing some benchmarking, and noticed some poor performance,
indicating that my overdrive settings were not in place, which they
were. hwmon/power1_cap reports the correctly adjusted value after it is
written to, and I confirmed with a quick patch that the updated power
limit value is actually
