Documentation: gpio: driver.rst: Fix warnings

This document serves as a guide for writers of GPIO chip drivers.

Each GPIO controller driver needs to include the following header, which defines

the structures used to define a GPIO driver:

the structures used to define a GPIO driver::

	#include <linux/gpio/driver.h>

under the assumption that your interrupts are 1-to-1-mapped to the

GPIO line index:

  GPIO line offset   Hardware IRQ

  0                  0

  1                  1

  2                  2

  ...                ...

  ngpio-1            ngpio-1

.. csv-table::

    :header: GPIO line offset, Hardware IRQ

    0,0

    1,1

    2,2

    ...,...

    ngpio-1, ngpio-1

If some GPIO lines do not have corresponding IRQs, the bitmask valid_mask

and the flag need_valid_mask in gpio_irq_chip can be used to mask off some

struct gpio_irq_chip inside struct gpio_chip before adding the gpio_chip.

If you do this, the additional irq_chip will be set up by gpiolib at the

same time as setting up the rest of the GPIO functionality. The following

is a typical example of a cascaded interrupt handler using gpio_irq_chip:

is a typical example of a cascaded interrupt handler using gpio_irq_chip::

.. code-block:: c

  return devm_gpiochip_add_data(dev, &g->gc, g);

The helper support using hierarchical interrupt controllers as well.

In this case the typical set-up will look like this:

In this case the typical set-up will look like this::

.. code-block:: c