LED驱动开发实例
本小节简单描述Linux内核中的LED驱动程序，通过LED的设备定义、管脚配置和设备访问的代码来展示LED驱动程序的设计。
设备定义
linux-3.2.0/arch/arm/mach-omap2/board-am335xevm.c
配置GPIO3.18为“sys_led”（系统心跳灯）、GPIO0.27，GPIO0.3为“user_led”，均为低电平有效：
static struct gpio_led gpio_leds[] = {
{
.name = "sys_led",
.default_trigger = "heartbeat",
.gpio = GPIO_TO_PIN(3, 18),
},
{
.name = "user_led0",
.gpio = GPIO_TO_PIN(0, 3),
},
{
.name = "user_led1",
.gpio = GPIO_TO_PIN(0, 27),
},
};
static struct gpio_led_platform_data gpio_led_info = {
.leds = gpio_leds,
.num_leds = ARRAY_SIZE(gpio_leds),
};
static struct platform_device leds_gpio = {
.name = "leds-gpio",
.id = -1,
.dev = {
.platform_data = &gpio_led_info,
},
};
- GPIO pinmux 配置
linux-3.2.0/arch/arm/mach-omap2/board-am335xevm.c
配置GPIO3.18、GPIO0.27、GPIO0.3为M7(gpio模式)、IDIS（不允许输入）：
static struct pinmux_config gpio_led_pin_mux[] = {
{"mcasp0_aclkr.gpio3_18",
OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT
},
{"spi0_d0.gpio0_3",
OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT
},
{"gpmc_ad11.gpio0_27",
OMAP_MUX_MODE7 | AM33XX_PIN_OUTPUT
},
{NULL, 0},
};
- 驱动设计
linux-3.2.0/drivers/leds/leds-gpio.c
调用platform_driver_register注册gpio_leds驱动：
static struct platform_driver gpio_led_driver = {
.probe = gpio_led_probe,
.remove = __devexit_p(gpio_led_remove),
.driver = {
.name = "leds-gpio",
.owner = THIS_MODULE,
.of_match_table = of_gpio_leds_match,
},
};
MODULE_ALIAS("platform:leds-gpio");
static int __init gpio_led_init(void)
{
return platform_driver_register(&gpio_led_driver);
}
static void __exit gpio_led_exit(void)
{
platform_driver_unregister(&gpio_led_driver);
}
module_init(gpio_led_init);
module_exit(gpio_led_exit);
MODULE_AUTHOR("Raphael Assenat <[email protected]>, Trent Piepho <[email protected]>");
MODULE_DESCRIPTION("GPIO LED driver");
MODULE_LICENSE("GPL");
申请gpio，调用led_classdev_register注册led_classdev驱动：
static int __devinit gpio_led_probe(struct platform_device *pdev)
{
struct gpio_led_platform_data *pdata = pdev->dev.platform_data;
struct gpio_leds_priv *priv;
int i, ret = 0;
if (pdata && pdata->num_leds) {
priv = kzalloc(sizeof_gpio_leds_priv(pdata->num_leds),
GFP_KERNEL);
if (!priv)
return -ENOMEM;
priv->num_leds = pdata->num_leds;
for (i = 0; i < priv->num_leds; i++) {
ret = create_gpio_led(&pdata->leds[i],
&priv->leds[i],
&pdev->dev, pdata->gpio_blink_set);
if (ret < 0) {
/* On failure: unwind the led creations */
for (i = i - 1; i >= 0; i--)
delete_gpio_led(&priv->leds[i]);
kfree(priv);
return ret;
}
}
} else {
priv = gpio_leds_create_of(pdev);
if (!priv)
return -ENODEV;
}
platform_set_drvdata(pdev, priv);
return 0;
}
static int __devinit create_gpio_led(const struct gpio_led *template,
struct gpio_led_data *led_dat, struct device *parent,
int (*blink_set)(unsigned, int, unsigned long *, unsigned long *))
{
int ret, 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);
return 0;
}
ret = gpio_request(template->gpio, template->name);
if (ret < 0)
return ret;
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)
goto err;
INIT_WORK(&led_dat->work, gpio_led_work);
ret = led_classdev_register(parent, &led_dat->cdev);
if (ret < 0)
goto err;
return 0;
err:
gpio_free(led_dat->gpio);
return ret;
}
用户通过访问/sys/class/leds/xxx/brightness文件，调用gpio_set_set函数，控制led灯的状态（在这里，“xxx”对应sys_led、user_led0、user_led1中的任何一个）：
static void gpio_led_set(struct led_classdev *led_cdev,
enum led_brightness value)
{
struct gpio_led_data *led_dat =
container_of(led_cdev, struct gpio_led_data, cdev);
int level;
if (value == LED_OFF)
level = 0;
else
level = 1;
if (led_dat->active_low)
level = !level;
/* Setting GPIOs with I2C/etc requires a task context, and we don't
* seem to have a reliable way to know if we're already in one; so
* let's just assume the worst.
*/
if (led_dat->can_sleep) {
led_dat->new_level = level;
schedule_work(&led_dat->work);
} else {
if (led_dat->blinking) {
led_dat->platform_gpio_blink_set(led_dat->gpio, level,
NULL, NULL);
led_dat->blinking = 0;
} else
gpio_set_value(led_dat->gpio, level);
}