Hmm, interestingly 82357B worked here, once. In fact, first time on RPI3, ever.
Took the v2 image, updated and rebuilt kernel then built linux-gpib with debug.
First ibterm with K2000 didn't work, then tried ibterm with K2400, which, surprisingly, did work.
Afterwards ibtest worked for both. Even ibterm with K2000 worked fine.
pi@pi3:~ $ sudo ibterm -d 1 -e 0x0a -b 1 -x 1
Attempting to open /dev/gpib0
pad = 1, sad = 0, timeout = 10, send_eoi = 1, eos_mode = 0x1800
ibterm>*idn?
ibterm error: Unable to write to device at pad 1
- EBUS 14: Bus error
ibterm>
ibterm: Done.
pi@pi3:~ $ sudo ibterm -d 24 -e 0x0a -b 1 -x 1
Attempting to open /dev/gpib0
pad = 24, sad = 0, timeout = 10, send_eoi = 1, eos_mode = 0x1800
ibterm>*idn?
KEITHLEY INSTRUMENTS INC.,MODEL 2400-C,1234567,C32 Oct 4 2010 14:20:11/A02 /G/H/E
ibterm>
ibterm: Done.
pi@pi3:~ $ sudo ibterm -d 1 -e 0x0a -b 1 -x 1
Attempting to open /dev/gpib0
pad = 1, sad = 0, timeout = 10, send_eoi = 1, eos_mode = 0x1800
ibterm>*idn?
KEITHLEY INSTRUMENTS INC.,MODEL 2000,1234567,A19 /A02
ibterm>
ibterm: Done.
After a reboot it doesn't work again. Doesn't matter whether ibtest or ibterm is tried.