By using 16-bit I/O on the GPIO peripheral, which is apparently not safe
on MIPS, the IMR can end up containing garbage. This then results in
interrupt triggers for lines that don't have an interrupt handler
associated. The irq_desc lookup fails, and the ISR will not be cleared,
keeping the CPU busy until reboot, or until another IMR operation
restores the correct value. This situation appears to happen very
rarely, for < 0.5% of IMR writes.

Instead of using 8-bit or 16-bit I/O operations on the 32-bit memory
mapped peripheral registers, switch to using 32-bit I/O only, operating
on the entire bank for all single bit line settings. For 2-bit line
settings, with 16-bit port values, stick to manual (un)packing.

This issue has been seen on RTL8382M (HPE 1920-16G), RTL8391M (Netgear
GS728TP v2), and RTL8393M (D-Link DGS-1210-52 F3, Zyxel GS1900-48).

Reported-by: Luiz Angelo Daros de Luca <luizluca@gmail.com> # DGS-1210-52
Reported-by: Birger Koblitz <mail@birger-koblitz.de> # GS728TP
Reported-by: Jan Hoffmann <jan@3e8.eu> # 1920-16G
Fixes: 0d82fb11 ("gpio: Add Realtek Otto GPIO support")
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Cc: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>