leds子系统-下
（本文内容涉及的代码全部取自linux-2.6.36内核中）
书接上文，洋洋洒洒的代码贴了那么多，不过好像并没有看到led子系统针对驱动开发用户的实际操作，下面就对gpio-led功能继续剖析：
1． Gpio-led初始化
drivers/leds/leds-gpio.c(line317-line348)
static int __init gpio_led_init(void)
{
intret;
#ifdef CONFIG_LEDS_GPIO_PLATFORM
ret= platform_driver_register(&gpio_led_driver);
if(ret)
returnret;
#endif
#ifdef CONFIG_LEDS_GPIO_OF
ret= of_register_platform_driver(&of_gpio_leds_driver);
#endif
#ifdef CONFIG_LEDS_GPIO_PLATFORM
if(ret)
platform_driver_unregister(&gpio_led_driver);
#endif
returnret;
}
static void __exit gpio_led_exit(void)
{
#ifdef CONFIG_LEDS_GPIO_PLATFORM
platform_driver_unregister(&gpio_led_driver);
#endif
#ifdef CONFIG_LEDS_GPIO_OF
of_unregister_platform_driver(&of_gpio_leds_driver);
#endif
}
module_init(gpio_led_init);
module_exit(gpio_led_exit);
gpio_led_init才是对led设备的实际注册功能，这就是前面提到的，在leds子系统初始化时使用的是subsys_initcall而不是module_init的原因。
在gpio_led_init初始化提供了struct platform_driver和structof_platform_driver两种结构可以选择。
2．
drivers/leds/leds-gpio.c(line205-line212)
static struct platform_drivergpio_led_driver = {
.probe = gpio_led_probe,
.remove = __devexit_p(gpio_led_remove),
.driver = {
.name = "leds-gpio",
.owner = THIS_MODULE,
},
};
3．
drivers/leds/leds-gpio.c(line155-line187)
static int __devinit gpio_led_probe(structplatform_device *pdev)
{
structgpio_led_platform_data *pdata = pdev->dev.platform_data;
structgpio_led_data *leds_data;
inti, ret = 0;
if(!pdata)
return-EBUSY;
leds_data= kzalloc(sizeof(struct gpio_led_data) * pdata->num_leds,
GFP_KERNEL);
if(!leds_data)
return-ENOMEM;
//创建gpio-led设备
for(i = 0; i < pdata->num_leds; i++) {
ret= create_gpio_led(&pdata->leds[i],&leds_data[i],
&pdev->dev,pdata->gpio_blink_set);
if(ret < 0)
gotoerr;
}
//创建设备链表
platform_set_drvdata(pdev,leds_data);
return0;
err:
for(i = i - 1; i >= 0; i--)
delete_gpio_led(&leds_data[i]);
kfree(leds_data);
returnret;
}
4．再让我们看看create_gpio_led这个函数的功能，这个函数对gpio的硬件功能进行初始化，这个函数用到我前面提过的led_classdev_register函数，所以这个函数应该实现的功能包括申请gpio资源、初始化gpio、创建创建一个struct device并且注册sysfs，生成/sys/class/leds目录与硬件相关。代码内容如下
static int __devinit create_gpio_led(conststruct gpio_led *template,
structgpio_led_data *led_dat, struct device *parent,
int(*blink_set)(unsigned, int, unsigned long *, unsigned long *))
{
intret, state;
led_dat->gpio= -1;
/*skip leds that aren't available */
if(!gpio_is_valid(template->gpio)) {
printk(KERN_INFO"Skipping unavailable LED gpio %d (%s)\n",
template->gpio,template->name);
return0;
}
ret= gpio_request(template->gpio, template->name);
if(ret < 0)
returnret;
led_dat->cdev.name= template->name;
led_dat->cdev.default_trigger= template->default_trigger;
led_dat->gpio= template->gpio;
led_dat->can_sleep= gpio_cansleep(template->gpio);
led_dat->active_low= template->active_low;
led_dat->blinking= 0;
if(blink_set) {
led_dat->platform_gpio_blink_set= blink_set;
led_dat->cdev.blink_set= gpio_blink_set;
}
led_dat->cdev.brightness_set= gpio_led_set;
if(template->default_state == LEDS_GPIO_DEFSTATE_KEEP)
state= !!gpio_get_value(led_dat->gpio) ^ led_dat->active_low;
else
state= (template->default_state == LEDS_GPIO_DEFSTATE_ON);
led_dat->cdev.brightness= state ? LED_FULL : LED_OFF;
if(!template->retain_state_suspended)
led_dat->cdev.flags|= LED_CORE_SUSPENDRESUME;
ret= gpio_direction_output(led_dat->gpio, led_dat->active_low ^ state);
if(ret < 0)
gotoerr;
INIT_WORK(&led_dat->work,gpio_led_work);
ret= led_classdev_register(parent,&led_dat->cdev);
if(ret < 0)
gotoerr;
return0;
err:
gpio_free(led_dat->gpio);
returnret;
}
module_init执行完成之后，一个真正的leds设备就真正创建完成了。
个人水平有限，还有很多错误和不足之处，望指正。