pinctrl: ingenic: Enhance support for IRQ_TYPE_EDGE_BOTH

commit 1c95348b upstream.

Ingenic SoCs don't natively support registering an interrupt for both
rising and falling edges. This has to be emulated in software.

Until now, this was emulated by switching back and forth between
IRQ_TYPE_EDGE_RISING and IRQ_TYPE_EDGE_FALLING according to the level of
the GPIO. While this worked most of the time, when used with GPIOs that
need debouncing, some events would be lost. For instance, between the
time a falling-edge interrupt happens and the interrupt handler
configures the hardware for rising-edge, the level of the pin may have
already risen, and the rising-edge event is lost.

To address that issue, instead of switching back and forth between
IRQ_TYPE_EDGE_RISING and IRQ_TYPE_EDGE_FALLING, we now switch back and
forth between IRQ_TYPE_LEVEL_LOW and IRQ_TYPE_LEVEL_HIGH. Since we
always switch in the interrupt handler, they actually permit to detect
level changes. In the example above, if the pin level rises before
switching the IRQ type from IRQ_TYPE_LEVEL_LOW to IRQ_TYPE_LEVEL_HIGH,
a new interrupt will raise as soon as the handler exits, and the
rising-edge event will be properly detected.

Fixes: e72394e2

 ("pinctrl: ingenic: Merge GPIO functionality")
Reported-by: João Henrique <johnnyonflame@hotmail.com>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: João Henrique <johnnyonflame@hotmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200622214548.265417-1-paul@crapouillou.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>