一、Backlight背光子系统概述
LCD的背光原理主要是由核心板的一根引脚控制背光电源，一根PWM引脚控制背光亮度组成，应用程序可以通过改变PWM的频率达到改变背光亮度的目的。
二、PWM核心驱动
代码/arch/arm/plat-samsung/pwm.c
内核中需要使能“PWM device support”
System Type -->
[*]PWM device support它是
pwm核心驱动，该驱动把设备和驱动没有分离开来，都写在了这个
pwm.c中，我们先看看
pwm.c中的驱动部分
static int __init pwm_init(void)
{
int ret;
clk_scaler[0] = clk_get(NULL, "pwm-scaler0");//获取0号时钟
clk_scaler[1] = clk_get(NULL, "pwm-scaler1");//获取1号时钟
if (IS_ERR(clk_scaler[0]) || IS_ERR(clk_scaler[1])) {
printk(KERN_ERR "%s: failed to get scaler clocks\n", __func__);
return -EINVAL;
}
ret = platform_driver_register(&s3c_pwm_driver);//注册pwm驱动
if (ret)
printk(KERN_ERR "%s: failed to add pwm driver\n", __func__);
return ret;
}
//s3c_pwm_driver定义
static struct platform_driver s3c_pwm_driver = {
.driver = {
.name = "s3c24xx-pwm",//驱动名
.owner = THIS_MODULE,
},
.probe = s3c_pwm_probe,//探测函数
.remove = __devexit_p(s3c_pwm_remove),
.suspend = s3c_pwm_suspend,
.resume = s3c_pwm_resume,
};
三、Backlight核心驱动
代码/driver/video/backlight/backlight.c
内核中需要使能“Lowlevel Backlight controls”
Device Drivers --->
Graphics support ---> [*] Backlight & LCD device support ---> <*> Lowlevel Backlight controls
代码分析
static int __init backlight_class_init(void)
{
backlight_class = class_create(THIS_MODULE, "backlight");//在/sys/class下注册backlight类
if (IS_ERR(backlight_class)) {
printk(KERN_WARNING "Unable to create backlight class; errno = %ld\n",
PTR_ERR(backlight_class));
return PTR_ERR(backlight_class);
}
backlight_class->dev_attrs = bl_device_attributes;//添加类属性
backlight_class->suspend = backlight_suspend;
backlight_class->resume = backlight_resume;
return 0;
}
backlight背光系统的主要就是靠这个类属性，设置背光值就是向这个类属性中某个成员写入背光值，这个类属性就是给用户的同一接口
#define __ATTR(_name,_mode,_show,_store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, \
}
static struct device_attribute bl_device_attributes[] = {
__ATTR(bl_power, 0644, backlight_show_power, backlight_store_power),
__ATTR(brightness, 0644, backlight_show_brightness,
backlight_store_brightness),
__ATTR(actual_brightness, 0444, backlight_show_actual_brightness,
NULL),
__ATTR(max_brightness, 0444, backlight_show_max_brightness, NULL),
__ATTR(type, 0444, backlight_show_type, NULL),
__ATTR_NULL,
};很明显，在backlight类中我们创建了bl_power，brightness，actural_brightness，max_brightness四个成员，其中brightness是当前亮度，max_brightness是最大亮度。当用户层通过cat或者echo命令就会触发这些成员。对于这些属性的读写函数，我们先看看读的函数backlight_show_max_brightness吧
static ssize_t backlight_show_max_brightness(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct backlight_device *bd = to_backlight_device(dev);
return sprintf(buf, "%d\n", bd->props.max_brightness);//输出最大亮度
}
这个函数很简单，但是重点是引入了几个backlight背光子系统的几个重要的数据结构，我们好好学习下。
首先是backlight背光子系统的设备结构体backlight_device
struct backlight_device {
/* Backlight properties */
struct backlight_properties props;//背光属性
/* Serialise access to update_status method */
struct mutex update_lock;
/* This protects the 'ops' field. If 'ops' is NULL, the driver that
registered this device has been unloaded, and if class_get_devdata()
points to something in the body of that driver, it is also invalid. */
struct mutex ops_lock;
const struct backlight_ops *ops;//背光操作函数，类似于file_operation
/* The framebuffer notifier block */
struct notifier_block fb_notif;
struct device dev;//内嵌设备
};
下面先看看背光属性结构体backlight_properties
struct backlight_properties {
/* Current User requested brightness (0 - max_brightness) */
int brightness;//当前背光值
/* Maximal value for brightness (read-only) */
int max_brightness;//最大背光值
/* Current FB Power mode (0: full on, 1..3: power saving
modes; 4: full off), see FB_BLANK_XXX */
int power;
/* FB Blanking active? (values as for power) */
/* Due to be removed, please use (state & BL_CORE_FBBLANK) */
int fb_blank;
/* Backlight type */
enum backlight_type type;
/* Flags used to signal drivers of state changes */
/* Upper 4 bits are reserved for driver internal use */
unsigned int state;
#define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */
#define BL_CORE_FBBLANK (1 << 1) /* backlight is under an fb blank event */
#define BL_CORE_DRIVER4 (1 << 28) /* reserved for driver specific use */
#define BL_CORE_DRIVER3 (1 << 29) /* reserved for driver specific use */
#define BL_CORE_DRIVER2 (1 << 30) /* reserved for driver specific use */
#define BL_CORE_DRIVER1 (1 << 31) /* reserved for driver specific use */
};
在看看背光操作函数
struct backlight_ops {
unsigned int options;
#define BL_CORE_SUSPENDRESUME (1 << 0)
/* Notify the backlight driver some property has changed */
int (*update_status)(struct backlight_device *);//更新背光状态
/* Return the current backlight brightness (accounting for power,
fb_blank etc.) */
int (*get_brightness)(struct backlight_device *);//获取背光值
/* Check if given framebuffer device is the one bound to this backlight;
return 0 if not, !=0 if it is. If NULL, backlight always matches the fb. */
int (*check_fb)(struct backlight_device *, struct fb_info *);
};当前背光值函数
backlight_store_brightness
static ssize_t backlight_store_brightness(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
int rc;
struct backlight_device *bd = to_backlight_device(dev);
unsigned long brightness;
rc = strict_strtoul(buf, 0, &brightness);
if (rc)
return rc;
rc = -ENXIO;
mutex_lock(&bd->ops_lock);
if (bd->ops) {
if (brightness > bd->props.max_brightness)
rc = -EINVAL;
else {
pr_debug("backlight: set brightness to %lu\n",
brightness);
bd->props.brightness = brightness;//传入背光值
backlight_update_status(bd);//更新背光状态
rc = count;
}
}
mutex_unlock(&bd->ops_lock);
backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
return rc;
}
static inline void backlight_update_status(struct backlight_device *bd)
{
mutex_lock(&bd->update_lock);
if (bd->ops && bd->ops->update_status)
bd->ops->update_status(bd);
mutex_unlock(&bd->update_lock);
}
对于这个backlight背光核心层驱动backlight.c，剩下的就是这个pwm.c给我们提供了哪些接口函数了
struct backlight_device *backlight_device_register(const char *name, struct device *parent, void *devdata, struct backlight_ops *ops) void backlight_device_unregister(struct backlight_device *bd) EXPORT_SYMBOL(backlight_device_register); //注册背光设备 EXPORT_SYMBOL(backlight_device_unregister); //注销背光设备
四、基于PWM&Backlight的蜂鸣器驱动
结合上面的 PWM核心层和 Backlight背光子系统核心层，根据基于 pwm的背光驱动 /driver/video/backlight/pwm_bl.c来修改成基于 tq210的蜂鸣器驱动内核中需要使能“Generic PWM based Backlight Driver”
Device Drivers --->
Graphics support ---> [*] Backlight & LCD device support ---> <*> Generic PWM based Backlight Driver
tq210蜂鸣器使用GPD0_1口，该端口工作在TOU0模式下，就可以通过设备定时器的TCNT和TCMP来控制定时器的波形。
首先，在tq210的BSP文件mach-tq210.c，如下添加
static struct platform_device tq210_backlight_device = {
.name = "pwm-backlight",//设备名
.dev = {
.parent = &s3c_device_timer[0].dev,//该设备基于pwm中的0号定时器
.platform_data = &tq_backlight_data,
},
};
添加平台数据
static struct platform_pwm_backlight_data tq210_backlight_data = {
.pwm_id = 0,//对应的就是Timer0
.max_brightness = 255,//最大亮度
.dft_brightness = 100,//255,//当前亮度
.lth_brightness = 50,//咱不知道干啥用的
.pwm_period_ns = 20000,//78770,//T0，即输出时钟周期
.init = tq210_backlight_init,//端口初始化
.exit = tq210_backlight_exit,
};
static int tq210_backlight_init(struct device *dev)
{
int ret;
ret = gpio_request(S5PV210_GPD0(0), "Backlight");
if (ret) {
printk(KERN_ERR "failed to request GPD for PWM-OUT 0\n");
return ret;
}
/* Configure GPIO pin with S5PV210_GPD_0_0_TOUT_0 */
s3c_gpio_cfgpin(S5PV210_GPD0(0), S3C_GPIO_SFN(2));
return 0;
}
static void tq210_backlight_exit(struct device *dev)
{
s3c_gpio_cfgpin(S5PV210_GPD0(0), S3C_GPIO_OUTPUT);
gpio_free(S5PV210_GPD0(0));
}
然后把tq210_backlight_device添加到tq210_devices数组
static struct platform_device *tq210_devices[] __initdata = {
...
#ifdef CONFIG_BACKLIGHT_PWM
&s3c_device_timer[0],
&s3c_device_timer[1],
&s3c_device_timer[2],
&s3c_device_timer[3],
&tq210_backlight_device,//同时添加对应的s3c_device_timer[0]
#endif
...
};
最后添加头文件
#include <linux/pwm_backlight.h>