[PATCH] gpio: aggregator: Add interrupt support

[Geert Uytterhoeven <geert+renesas@xxxxxxxxx>]

Currently the GPIO Aggregator does not support interrupts.  This means
that kernel drivers going from a GPIO to an IRQ using gpiod_to_irq(),
and userspace applications using line events do not work.

Add interrupt support by providing a gpio_chip.to_irq() callback, which
just calls into the parent GPIO controller.

Note that this does not implement full interrupt controller (irq_chip)
support, so using e.g. gpio-keys with "interrupts" instead of "gpios"
still does not work.

Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
---
I would prefer to avoid implementing irq_chip support, until there is a
real use case for this.

This has been tested with gpio-keys and gpiomon on the Koelsch
development board:

  - gpio-keys, using a DT overlay[1]:

	$ overlay add r8a7791-koelsch-keyboard-controlled-led
	$ echo gpio-aggregator > /sys/devices/platform/frobnicator/driver_override
	$ echo frobnicator > /sys/bus/platform/drivers/gpio-aggregator/bind

	$ gpioinfo frobnicator
	gpiochip12 - 3 lines:
		line   0:      "light"      "light"  output  active-high [used]
		line   1:         "on"         "On"   input   active-low [used]
		line   2:        "off"        "Off"   input   active-low [used]

	$ echo 255 > /sys/class/leds/light/brightness
	$ echo 0 > /sys/class/leds/light/brightness

	$ evtest /dev/input/event0

  - gpiomon, using the GPIO sysfs API:

	$ echo keyboard > /sys/bus/platform/drivers/gpio-keys/unbind
	$ echo e6055800.gpio 2,6 > /sys/bus/platform/drivers/gpio-aggregator/new_device
	$ gpiomon gpiochip12 0 1

[1] "ARM: dts: koelsch: Add overlay for keyboard-controlled LED"
    https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/commit/?h=topic/renesas-overlays&id=c78d817869e63a3485bb4ab98aeea6ce368a396e
---
 drivers/gpio/gpio-aggregator.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-aggregator.c b/drivers/gpio/gpio-aggregator.c
index 34e35b64dcdc0581..2ff867d2a3630d3b 100644
--- a/drivers/gpio/gpio-aggregator.c
+++ b/drivers/gpio/gpio-aggregator.c
@@ -374,6 +374,13 @@ static int gpio_fwd_set_config(struct gpio_chip *chip, unsigned int offset,
 	return gpiod_set_config(fwd->descs[offset], config);
 }
 
+static int gpio_fwd_to_irq(struct gpio_chip *chip, unsigned int offset)
+{
+	struct gpiochip_fwd *fwd = gpiochip_get_data(chip);
+
+	return gpiod_to_irq(fwd->descs[offset]);
+}
+
 /**
  * gpiochip_fwd_create() - Create a new GPIO forwarder
  * @dev: Parent device pointer
@@ -414,7 +421,8 @@ static struct gpiochip_fwd *gpiochip_fwd_create(struct device *dev,
 	for (i = 0; i < ngpios; i++) {
 		struct gpio_chip *parent = gpiod_to_chip(descs[i]);
 
-		dev_dbg(dev, "%u => gpio-%d\n", i, desc_to_gpio(descs[i]));
+		dev_dbg(dev, "%u => gpio %d irq %d\n", i,
+			desc_to_gpio(descs[i]), gpiod_to_irq(descs[i]));
 
 		if (gpiod_cansleep(descs[i]))
 			chip->can_sleep = true;
@@ -432,6 +440,7 @@ static struct gpiochip_fwd *gpiochip_fwd_create(struct device *dev,
 	chip->get_multiple = gpio_fwd_get_multiple_locked;
 	chip->set = gpio_fwd_set;
 	chip->set_multiple = gpio_fwd_set_multiple_locked;
+	chip->to_irq = gpio_fwd_to_irq;
 	chip->base = -1;
 	chip->ngpio = ngpios;
 	fwd->descs = descs;
-- 
2.25.1