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 <[email protected]>
---
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 e9671d1660ef4b40..869dc952cf45218b 100644
--- a/drivers/gpio/gpio-aggregator.c
+++ b/drivers/gpio/gpio-aggregator.c
@@ -371,6 +371,13 @@ 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
@@ -411,7 +418,8 @@ 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;
@@ -429,6 +437,7 @@ 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

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