处理器：i.MX 6Quad

内核：Linux version 3.0.35

参考内核说明文档：Documentation/gpio.txt

通用GPIO输入输出使用：

Using GPIOs
-----------
The first thing a system should do with a GPIO is allocate it, using
the gpio_request() call; see later.

One of the next things to do with a GPIO, often in board setup code when
setting up a platform_device using the GPIO, is mark its direction:

	/* set as input or output, returning 0 or negative errno */
	int gpio_direction_input(unsigned gpio);
	int gpio_direction_output(unsigned gpio, int value);

The return value is zero for success, else a negative errno.  It should
be checked, since the get/set calls don't have error returns and since
misconfiguration is possible.  You should normally issue these calls from
a task context.  However, for spinlock-safe GPIOs it's OK to use them
before tasking is enabled, as part of early board setup.

For output GPIOs, the value provided becomes the initial output value.
This helps avoid signal glitching during system startup.

For compatibility with legacy interfaces to GPIOs, setting the direction
of a GPIO implicitly requests that GPIO (see below) if it has not been
requested already.  That compatibility is being removed from the optional
gpiolib framework.

Setting the direction can fail if the GPIO number is invalid, or when
that particular GPIO can't be used in that mode.  It's generally a bad
idea to rely on boot firmware to have set the direction correctly, since
it probably wasn't validated to do more than boot Linux.  (Similarly,
that board setup code probably needs to multiplex that pin as a GPIO,
and configure pullups/pulldowns appropriately.)


Spinlock-Safe GPIO access
-------------------------
Most GPIO controllers can be accessed with memory read/write instructions.
Those don't need to sleep, and can safely be done from inside hard
(nonthreaded) IRQ handlers and similar contexts.

Use the following calls to access such GPIOs,
for which gpio_cansleep() will always return false (see below):

	/* GPIO INPUT:  return zero or nonzero */
	int gpio_get_value(unsigned gpio);

	/* GPIO OUTPUT */
	void gpio_set_value(unsigned gpio, int value);

The values are boolean, zero for low, nonzero for high.  When reading the
value of an output pin, the value returned should be what's seen on the
pin ... that won't always match the specified output value, because of
issues including open-drain signaling and output latencies.

The get/set calls have no error returns because "invalid GPIO" should have
been reported earlier from gpio_direction_*().  However, note that not all
platforms can read the value of output pins; those that can't should always
return zero.  Also, using these calls for GPIOs that can't safely be accessed
without sleeping (see below) is an error.

Platform-specific implementations are encouraged to optimize the two
calls to access the GPIO value in cases where the GPIO number (and for
output, value) are constant.  It's normal for them to need only a couple
of instructions in such cases (reading or writing a hardware register),
and not to need spinlocks.  Such optimized calls can make bitbanging
applications a lot more efficient (in both space and time) than spending
dozens of instructions on subroutine calls.

GPIO中断配置：

GPIOs mapped to IRQs
--------------------
GPIO numbers are unsigned integers; so are IRQ numbers.  These make up
two logically distinct namespaces (GPIO 0 need not use IRQ 0).  You can
map between them using calls like:

	/* map GPIO numbers to IRQ numbers */
	int gpio_to_irq(unsigned gpio);

	/* map IRQ numbers to GPIO numbers (avoid using this) */
	int irq_to_gpio(unsigned irq);

Those return either the corresponding number in the other namespace, or
else a negative errno code if the mapping can't be done.  (For example,
some GPIOs can't be used as IRQs.)  It is an unchecked error to use a GPIO
number that wasn't set up as an input using gpio_direction_input(), or
to use an IRQ number that didn't originally come from gpio_to_irq().

These two mapping calls are expected to cost on the order of a single
addition or subtraction.  They're not allowed to sleep.

Non-error values returned from gpio_to_irq() can be passed to request_irq()
or free_irq().  They will often be stored into IRQ resources for platform
devices, by the board-specific initialization code.  Note that IRQ trigger
options are part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are
system wakeup capabilities.

Non-error values returned from irq_to_gpio() would most commonly be used
with gpio_get_value(), for example to initialize or update driver state
when the IRQ is edge-triggered.  Note that some platforms don't support
this reverse mapping, so you should avoid using it.

1、使用gpio_to_irq函数获取相应的GPIO中断号

2、使用request_irq函数向内核注册中断

ps：以上函数中的GPIO参数说明，eg：设置GPIO2_IO00为输入模式，则使用函数gpio_direction_input（IMX_GPIO_NR(2, 0)）

/* There's a off-by-one betweem the gpio bank number and the gpiochip */
/* range e.g. GPIO_1_5 is gpio 5 under linux */
#define IMX_GPIO_NR(bank, nr)		(((bank) - 1) * 32 + (nr))