linux的gpio操作的api寻找
授人以鱼不如授人以渔，那么，拿人以鱼不如学人以渔
在有需求的时候能够找到对应的寻找点，那么就成功了
文件drivers/gpio/gpiolib.c，所需要的gpio的api都在里面了，例如
/**
* gpio_export - export a GPIO through sysfs gpio在sysfs的出口，供用户使用
* @gpio: gpio to make available, already requested
* @direction_may_change: true if userspace may change gpio direction
* Context: arch_initcall or later
*
* When drivers want to make a GPIO accessible to userspace after they
* have requested it -- perhaps while debugging, or as part of their
* public interface -- they may use this routine. If the GPIO can
* change direction (some can't) and the caller allows it, userspace
* will see "direction" sysfs attribute which may be used to change
* the gpio's direction. A "value" attribute will always be provided.
*
* Returns zero on success, else an error.
*/
static int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
/**
* gpio_sysfs_set_active_low - set the polarity of gpio sysfs value
* @gpio: gpio to change
* @value: non-zero to use active low, i.e. inverted values
*
* Set the polarity of /sys/class/gpio/gpioN/value sysfs attribute.
* The GPIO does not have to be exported yet. If poll(2) support has
* been enabled for either rising or falling edge, it will be
* reconfigured to follow the new polarity.
*
* Returns zero on success, else an error.
*/
static int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
/* Drivers MUST set GPIO direction before making get/set calls. In
* some cases this is done in early boot, before IRQs are enabled.
*
* As a rule these aren't called more than once (except for drivers
* using the open-drain emulation idiom) so these are natural places
* to accumulate extra debugging checks. Note that we can't (yet)
* rely on gpio_request() having been called beforehand.
*/
static int gpiod_direction_input(struct gpio_desc *desc)
总结
通过以上的几个例子可以看出对应的api都做了些什么事情，方向指在这里，大致掌握一遍，知道有哪些东西，知道可以用来做哪些事，真正需要的时候来这里调用，这已经成了应用工程师做的事情了。