就在目录/sys/class/leds创建子目录 lcd-backlight和属性文件brightness
当按键或者来的或者改变lcd亮度时，上层对属性文件/sys/class/leds/lcd-backlight/brightness写入背光的亮度数值就
调用led_brightness_store
调用simple_strtoul(buf, &after, 10);将输入的字符串转换为10进制的数字
执行led_set_brightness
执行led_cdev->brightness_set(led_cdev, value
调用msm_fb_set_bl_brightness ，因为 .brightness_set = msm_fb_set_bl_brightness,
/* This maps Android backlight level 0 to 255 into driver backlight level 0 to bl_max with rounding */
bl_lvl = (2 * value * mfd->panel_info.bl_max + MAX_BACKLIGHT_BRIGHTNESS) /(2 * MAX_BACKLIGHT_BRIGHTNESS);
将输入的0--255转换为IC的0--bl_max
调用 msm_fb_set_backlight(mfd, bl_lvl, 1);
最终改变LCD的背光驱动电路的设置，调节LCD的背光的亮度
4.4 键盘背光灯
上层对属性文件/sys/class/leds/keyboard-backlight/brightness写入背光的亮度数值
(kernel\drivers\leds\Leds-msm-pmic.c
#define MAX_KEYPAD_BL_LEVEL 16
static void msm_keypad_bl_led_set(struct led_classdev *led_cdev,
enum led_brightness value)
{
int ret;
ret = pmic_set_led_intensity(LED_KEYPAD, value / MAX_KEYPAD_BL_LEVEL);
if (ret)
dev_err(led_cdev->dev, "can't set keypad backlight\n");
}
static struct led_classdev msm_kp_bl_led = {
.name = "keyboard-backlight",
.brightness_set = msm_keypad_bl_led_set,
.brightness = LED_OFF,
};
static int msm_pmic_led_probe(struct platform_device *pdev)
{
int rc;
rc = led_classdev_register(&pdev->dev, &msm_kp_bl_led);
if (rc) {
dev_err(&pdev->dev, "unable to register led class driver\n");
return rc;
}
msm_keypad_bl_led_set(&msm_kp_bl_led, LED_OFF);
return rc;
}
static int __devexit msm_pmic_led_remove(struct platform_device *pdev)
{
led_classdev_unregister(&msm_kp_bl_led);
return 0;
}
#ifdef CONFIG_PM
static int msm_pmic_led_suspend(struct platform_device *dev,
pm_message_t state)
{
led_classdev_suspend(&msm_kp_bl_led);
return 0;
}
static int msm_pmic_led_resume(struct platform_device *dev)
{
led_classdev_resume(&msm_kp_bl_led);
return 0;
}
#else
#define msm_pmic_led_suspend NULL
#define msm_pmic_led_resume NULL
#endif
static struct platform_driver msm_pmic_led_driver = {
.probe = msm_pmic_led_probe,
.remove = __devexit_p(msm_pmic_led_remove),
.suspend = msm_pmic_led_suspend,
.resume = msm_pmic_led_resume,
.driver = {
.name = "pmic-leds",
.owner = THIS_MODULE,
},
};
static int __init msm_pmic_led_init(void)
{
return platform_driver_register(&msm_pmic_led_driver);
}
module_init(msm_pmic_led_init);
static void __exit msm_pmic_led_exit(void)
{
platform_driver_unregister(&msm_pmic_led_driver);
}
module_exit(msm_pmic_led_exit);
MODULE_DESCRIPTION("MSM PMIC LEDs driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:p