转自：http://blog.csdn.net/weiqing1981127/article/details/8515847
版权所有，转载必须说明转自 http://my.csdn.net/weiqing1981127
原创作者：南京邮电大学 通信与信息系统专业 研二 魏清
三．Backlight核心驱动
下面我们讲讲backlight子系统。背光子系统目录在/driver/video/backlight下，其中背光子系统核心代码是backlight.c
先查看/driver/video/backlight/Makefile
obj-$(CONFIG_BACKLIGHT_CLASS_DEVICE) += backlight.o
继续查看/driver/video/backlight/Kconfig
config BACKLIGHT_CLASS_DEVICE
tristate "Lowlevel Backlight controls"
depends on BACKLIGHT_LCD_SUPPORT
default m
所以配置内核make menuconfig时，需要选中这一项。
下面看backlight背光的核心代码backlight.c
static int __init backlight_class_init(void)
{
backlight_class = class_create(THIS_MODULE, "backlight"); //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;
}
我们知道backlight背光子系统的主要就是靠这个类属性，当我们设置背光值就是向类属性中某个成员写背光值，这个类属性就是给用户的一种接口，我们重点看看
#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_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 {
struct backlight_properties props; //背光属性
struct mutex update_lock;
struct mutex ops_lock;
struct backlight_ops *ops; //背光操作函数，类似于file_operations
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 {
int brightness; //当前背光值
int max_brightness; //最大背光值
int power;
int fb_blank;
unsigned int state;
};
再看看背光操作函数结构体
struct backlight_ops {
unsigned int options;
#define BL_CORE_SUSPENDRESUME (1 << 0)
int (*update_status)(struct backlight_device *); //改变背光状态
int (*get_brightness)(struct backlight_device *); //获取背光值
int (*check_fb)(struct fb_info *);
};
好了，我们继续看backlight类属性中写的函数，例如设置当前背光值函数backlight_store_brightness吧
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); //调用backlight_update_status设备背光值
rc = count;
}
}
mutex_unlock(&bd->ops_lock);
backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
return rc;
}
跟踪backlight_update_status
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); //调用背光操作函数中改变背光状态函数update_status
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
这些接口很简单，就不细说了，这样我们的backlight子系统的核心层就介绍完了。
四．基于PWM&Backlight的蜂鸣器驱动
下面我们结合上面的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Mini2440的蜂鸣器驱动。
先查看/driver/video/backlight/Makefile
obj-$(CONFIG_BACKLIGHT_PWM) += pwm_bl.o
继续查看/driver/video/backlight/Kconfig
config BACKLIGHT_PWM
tristate "Generic PWM based Backlight Driver"
depends on BACKLIGHT_CLASS_DEVICE && HAVE_PWM
help
If you have a LCD backlight adjustable by PWM, say Y to enable
this driver.
我们的HAVE_PWM和BACKLIGHT_CLASS_DEVICE分别是在前面讲pwm核心和backlight核心时已经编译了，所以配置内核make menuconfig 时，需要再选中"Generic PWM based Backlight Driver"这项。
好了，我们先把我们的蜂鸣器移植进去吧，首先我们知道蜂鸣器使用的是GPB0端口，该端口如果工作在TOU0模式，就可以通过设备定时器的TCNT和TCMP来控制定时器的波形而来。先打开mini2440的BSP文件mach-mini2440.c，如下添加
static struct platform_device s3c_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 = &s3c_backlight_data,
},
.id=0, //对应的就是pwm0
};
添加平台数据
static struct platform_pwm_backlight_data s3c_backlight_data = {
.pwm_id = 0, //对应的就是Timer0
.max_brightness = 1000, //最大亮度
.dft_brightness = 10 , //当前亮度
.pwm_period_ns = 800000, //这就是前面说的T0，即输出时钟周期
.init = s3c_bl_init, //端口初始化
};
注意到平台数据中定义了init函数，由于在蜂鸣器的初始化时，需要对GPB0设置为TOUT0模式，所以代码如下编写
static int s3c_bl_init(struct device *dev)
{
s3c2410_gpio_pullup(S3C2410_GPB(0),0); // GPB0不上拉
s3c2410_gpio_cfgpin(S3C2410_GPB(0),S3C2410_GPB0_TOUT0); // GPB0设置为TOUT0
return 0;
}
然后把这个s3c_backlight_device加入到mini2440_devices数组
static struct platform_device *mini2440_devices[] __initdata = {
……
&s3c_device_timer[0],
&s3c_backlight_device, //添加
};
最后添加头文件
#include <linux/pwm_backlight.h>
这样配置完后，进行make zImage生成zImage内核镜像。
好了，下面我们分析下基于pwm的背光驱动/driver/video/backlight/pwm_bl.c
static struct platform_driver pwm_backlight_driver = {
.driver = {
.name = "pwm-backlight", //驱动名
.owner = THIS_MODULE,
},
.probe = pwm_backlight_probe, //探测函数
.remove = pwm_backlight_remove,
.suspend = pwm_backlight_suspend,
.resume = pwm_backlight_resume,
};
static int __init pwm_backlight_init(void)
{
return platform_driver_register(&pwm_backlight_driver);
}
注意上面的pwm_backlight_driver中的驱动名"pwm-backlight"和我们刚才移植时添加的设备名"pwm-backlight"是一致的，这样设备和驱动就能匹配成功。下面看探测函数
static int pwm_backlight_probe(struct platform_device *pdev)
{
struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
struct backlight_device *bl;
struct pwm_bl_data *pb; //本驱动的私有结构体
int ret;
if (!data) {
dev_err(&pdev->dev, "failed to find platform data\n");
return -EINVAL;
}
if (data->init) { //初始化端口，这个端口函数在BSP中定义
ret = data->init(&pdev->dev);
if (ret < 0)
return ret;
}
pb = kzalloc(sizeof(*pb), GFP_KERNEL); //分配pwm_bl_data空间
if (!pb) {
dev_err(&pdev->dev, "no memory for state\n");
ret = -ENOMEM;
goto err_alloc;
}
pb->period = data->pwm_period_ns; //获取周期
pb->notify = data->notify;
pb->pwm = pwm_request(data->pwm_id, "backlight"); //注册pwm设备
if (IS_ERR(pb->pwm)) {
dev_err(&pdev->dev, "unable to request PWM for backlight\n");
ret = PTR_ERR(pb->pwm);
goto err_pwm;
} else
dev_dbg(&pdev->dev, "got pwm for backlight\n");
bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev,
pb, &pwm_backlight_ops); //注册backlight设备
if (IS_ERR(bl)) {
dev_err(&pdev->dev, "failed to register backlight\n");
ret = PTR_ERR(bl);
goto err_bl;
}
bl->props.max_brightness = data->max_brightness;
bl->props.brightness = data->dft_brightness;
backlight_update_status(bl); //先点亮背光
platform_set_drvdata(pdev, bl); //设置bl为私有数据
return 0;
err_bl:
pwm_free(pb->pwm);
err_pwm:
kfree(pb);
err_alloc:
if (data->exit)
data->exit(&pdev->dev);
return ret;
}
对于这个驱动，我们重点关注的是注册backlight设备时传入的参数pwm_backlight_ops，因为我们之前分析backlight背光子系统时说过，背光设备结构体中有个操作背光的函数集合，在我们的pwm_bl.c中，就需要定义这个操作背光的函数集合，也就是pwm_backlight_ops
static struct backlight_ops pwm_backlight_ops = {
.update_status = pwm_backlight_update_status, //更新背光亮度
.get_brightness = pwm_backlight_get_brightness, //获取背光亮度
};
获取背光亮度函数pwm_backlight_get_brightness很简单，跟踪得到
static int pwm_backlight_get_brightness(struct backlight_device *bl)
{
return bl->props.brightness;
}
我们重点看更新背光亮度函数pwm_backlight_update_status
static int pwm_backlight_update_status(struct backlight_device *bl)
{
struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
int brightness = bl->props.brightness;
int max = bl->props.max_brightness;
if (bl->props.power != FB_BLANK_UNBLANK)
brightness = 0;
if (bl->props.fb_blank != FB_BLANK_UNBLANK)
brightness = 0;
if (pb->notify)
brightness = pb->notify(brightness);
if (brightness == 0) { //背光值为0，关闭背光
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
} else { //调用pwm中的API设置背光
pwm_config(pb->pwm, brightness * pb->period / max, pb->period);
pwm_enable(pb->pwm);
}
return 0;
}
好了，这样我们的pwm_bl.c也分析完了。在使用backlight子系统的时候，我们只需要在probe函数中注册pwm和backlight设备，然后定义背光操作函数集合即可。
五．驱动测试
实验环境：内核linux2.6.32.2，arm-linux-gcc交叉编译器，mini2440开发板
下面我们进行对上面的驱动进行测试，按照上面的步骤操作，将上文已经编译好的zImage烧入开发板，通过超级终端控制，能控制蜂鸣器的发出的声音频率。
