gpiolib: Initialize the hardware with a callback

After changing the drivers to use GPIO core to add an IRQ chip
it appears that some of them requires a hardware initialization
before adding the IRQ chip.

Add an optional callback ->init_hw() to allow that drivers
to initialize hardware if needed.

This change is a part of the fix NULL pointer dereference
brought to the several drivers recently.

Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -86,6 +86,7 @@ static int gpiochip_add_irqchip(struct gpio_chip *gpiochip,
 				struct lock_class_key *lock_key,
 				struct lock_class_key *request_key);
 static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip);
+static int gpiochip_irqchip_init_hw(struct gpio_chip *gpiochip);
 static int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gpiochip);
 static void gpiochip_irqchip_free_valid_mask(struct gpio_chip *gpiochip);
 
@@ -1406,6 +1407,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data,
 
 	machine_gpiochip_add(chip);
 
+	ret = gpiochip_irqchip_init_hw(chip);
+	if (ret)
+		goto err_remove_acpi_chip;
+
 	ret = gpiochip_irqchip_init_valid_mask(chip);
 	if (ret)
 		goto err_remove_acpi_chip;
@@ -1622,6 +1627,16 @@ static struct gpio_chip *find_chip_by_name(const char *name)
  * The following is irqchip helper code for gpiochips.
  */
 
+static int gpiochip_irqchip_init_hw(struct gpio_chip *gc)
+{
+	struct gpio_irq_chip *girq = &gc->irq;
+
+	if (!girq->init_hw)
+		return 0;
+
+	return girq->init_hw(gc);
+}
+
 static int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gc)
 {
 	struct gpio_irq_chip *girq = &gc->irq;
@@ -2446,8 +2461,13 @@ static inline int gpiochip_add_irqchip(struct gpio_chip *gpiochip,
 {
 	return 0;
 }
-
 static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip) {}
+
+static inline int gpiochip_irqchip_init_hw(struct gpio_chip *gpiochip)
+{
+	return 0;
+}
+
 static inline int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gpiochip)
 {
 	return 0;

include/linux/gpio/driver.h

@@ -201,6 +201,14 @@ struct gpio_irq_chip {
 	 */
 	bool threaded;
 
+	/**
+	 * @init_hw: optional routine to initialize hardware before
+	 * an IRQ chip will be added. This is quite useful when
+	 * a particular driver wants to clear IRQ related registers
+	 * in order to avoid undesired events.
+	 */
+	int (*init_hw)(struct gpio_chip *chip);
+
 	/**
 	 * @init_valid_mask: optional routine to initialize @valid_mask, to be
 	 * used if not all GPIO lines are valid interrupts. Sometimes some