LCD（五）Backlight背光子系統
阿新 • • 發佈：2019-01-24
一、Backlight背光子系統概述
LCD的背光原理主要是由核心板的一根引腳控制背光電源，一根PWM引腳控制背光亮度組成，應用程式可以通過改變PWM的頻率達到改變背光亮度的目的。
Backlight背光子系統構建過程結構關係圖
黑色加粗部分為開發人員需要填充的部分，其中pwm_id：第幾個定時器來做pwm；max_brightness背光調節範圍的最大值；dft_brightness：預設背光的當前值；pwm_period_ns：定時器週期；update_status()更新背光碟機動；get_brightness
二、PWM核心驅動
程式碼/arch/arm/plat-samsung/pwm.c核心中需要使能“PWM device support”
System Type -->
[*]PWM device supportstatic int __init pwm_init(void) { int ret; clk_scaler[0] = clk_get(NULL, "pwm-scaler0");//獲取0號時鐘 clk_scaler[1] = clk_get(NULL, "pwm-scaler1");//獲取1號時鐘 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);//註冊pwm驅動 if (ret) printk(KERN_ERR "%s: failed to add pwm driver\n", __func__); return ret; }
//s3c_pwm_driver定義
static struct platform_driver s3c_pwm_driver = {
.driver = {
.name = "s3c24xx-pwm",//驅動名
.owner = THIS_MODULE,
},
.probe = s3c_pwm_probe,//探測函式
.remove = __devexit_p(s3c_pwm_remove),
.suspend = s3c_pwm_suspend,
.resume = s3c_pwm_resume,
};探測函式
static int s3c_pwm_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; struct pwm_device *pwm; unsigned long flags; unsigned long tcon; unsigned int id = pdev->id; int ret; if (id == 4) { dev_err(dev, "TIMER4 is currently not supported\n"); return -ENXIO; } pwm = kzalloc(sizeof(struct pwm_device), GFP_KERNEL); if (pwm == NULL) { dev_err(dev, "failed to allocate pwm_device\n"); return -ENOMEM; } pwm->pdev = pdev; pwm->pwm_id = id; /* calculate base of control bits in TCON */ pwm->tcon_base = id == 0 ? 0 : (id * 4) + 4;//計算TCON中控制哪個定時器 pwm->clk = clk_get(dev, "pwm-tin");//獲取預分頻後的時鐘 if (IS_ERR(pwm->clk)) { dev_err(dev, "failed to get pwm tin clk\n"); ret = PTR_ERR(pwm->clk); goto err_alloc; } pwm->clk_div = clk_get(dev, "pwm-tdiv"); if (IS_ERR(pwm->clk_div)) {//獲取二次分屏後的時鐘 dev_err(dev, "failed to get pwm tdiv clk\n"); ret = PTR_ERR(pwm->clk_div); goto err_clk_tin; } local_irq_save(flags); tcon = __raw_readl(S3C2410_TCON); tcon |= pwm_tcon_invert(pwm);//訊號反轉輸出 __raw_writel(tcon, S3C2410_TCON); local_irq_restore(flags); ret = pwm_register(pwm);//註冊pwm裝置 if (ret) { dev_err(dev, "failed to register pwm\n"); goto err_clk_tdiv; } pwm_dbg(pwm, "config bits %02x\n", (__raw_readl(S3C2410_TCON) >> pwm->tcon_base) & 0x0f); dev_info(dev, "tin at %lu, tdiv at %lu, tin=%sclk, base %d\n", clk_get_rate(pwm->clk), clk_get_rate(pwm->clk_div), pwm_is_tdiv(pwm) ? "div" : "ext", pwm->tcon_base); platform_set_drvdata(pdev, pwm); return 0; err_clk_tdiv: clk_put(pwm->clk_div); err_clk_tin: clk_put(pwm->clk); err_alloc: kfree(pwm); return ret; }
pwm裝置函式的註冊pwm_register
static LIST_HEAD(pwm_list);
static DEFINE_MUTEX(pwm_lock);
static int pwm_register(struct pwm_device *pwm)
{
pwm->duty_ns = -1;
pwm->period_ns = -1;
mutex_lock(&pwm_lock);
list_add_tail(&pwm->list, &pwm_list);//把pwm裝置掛到pwm_list連結串列上
mutex_unlock(&pwm_lock);
return 0;
}pwm.c提供的介面函式
struct pwm_device *pwm_request(int pwm_id, const char *label)
int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
int pwm_enable(struct pwm_device *pwm)
void pwm_free(struct pwm_device *pwm)
EXPORT_SYMBOL(pwm_request); //申請PWM裝置
EXPORT_SYMBOL(pwm_config); //配置PWM裝置，duty_ns為空佔比，period_ns為週期
EXPORT_SYMBOL(pwm_enable); //啟動Timer定時器
EXPORT_SYMBOL(pwm_disable); //關閉Timer定時器int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
{
unsigned long tin_rate;
unsigned long tin_ns;
unsigned long period;
unsigned long flags;
unsigned long tcon;
unsigned long tcnt;
long tcmp;
/* We currently avoid using 64bit arithmetic by using the
* fact that anything faster than 1Hz is easily representable
* by 32bits. */
if (period_ns > NS_IN_HZ || duty_ns > NS_IN_HZ)
return -ERANGE;
if (duty_ns > period_ns)
return -EINVAL;
if (period_ns == pwm->period_ns &&
duty_ns == pwm->duty_ns)
return 0;
/* The TCMP and TCNT can be read without a lock, they're not
* shared between the timers. */
tcmp = __raw_readl(S3C2410_TCMPB(pwm->pwm_id));
tcnt = __raw_readl(S3C2410_TCNTB(pwm->pwm_id));
period = NS_IN_HZ / period_ns;//計算週期
pwm_dbg(pwm, "duty_ns=%d, period_ns=%d (%lu)\n",
duty_ns, period_ns, period);
/* Check to see if we are changing the clock rate of the PWM */
if (pwm->period_ns != period_ns) {
if (pwm_is_tdiv(pwm)) {
tin_rate = pwm_calc_tin(pwm, period);
clk_set_rate(pwm->clk_div, tin_rate);
} else
tin_rate = clk_get_rate(pwm->clk);
pwm->period_ns = period_ns;
pwm_dbg(pwm, "tin_rate=%lu\n", tin_rate);
tin_ns = NS_IN_HZ / tin_rate;
tcnt = period_ns / tin_ns;//根據週期求TCNT，n=To/Ti
} else
tin_ns = NS_IN_HZ / clk_get_rate(pwm->clk);
/* Note, counters count down */
tcmp = duty_ns / tin_ns;
tcmp = tcnt - tcmp;//根據佔空比求TCMP
/* the pwm hw only checks the compare register after a decrement,
so the pin never toggles if tcmp = tcnt */
if (tcmp == tcnt)
tcmp--;
pwm_dbg(pwm, "tin_ns=%lu, tcmp=%ld/%lu\n", tin_ns, tcmp, tcnt);
if (tcmp < 0)
tcmp = 0;
/* Update the PWM register block. */
local_irq_save(flags);
__raw_writel(tcmp, S3C2410_TCMPB(pwm->pwm_id));//寫入TCMp
__raw_writel(tcnt, S3C2410_TCNTB(pwm->pwm_id));//寫入TCNT
tcon = __raw_readl(S3C2410_TCON);
tcon |= pwm_tcon_manulupdate(pwm);
tcon |= pwm_tcon_autoreload(pwm);//自動載入
__raw_writel(tcon, S3C2410_TCON);
tcon &= ~pwm_tcon_manulupdate(pwm);//更新TCNT和TCMP
__raw_writel(tcon, S3C2410_TCON);
local_irq_restore(flags);
return 0;
}我們定時器的輸出頻率fi=PCLK/(prescaler value+1)/(divider value)，這個可以獲得確定值
我們需要寫入一個初值n給TCNT，這樣就可以獲得一個頻率，為什麼呢？
根據初值n=fi/fo，那麼n=To/Ti
所以當用戶給pwm_config函式傳遞一個週期period_ns，其實就是To=period_ns
這樣根據前面公式n=To/Ti= period_ns/fi，然後將這個初值n寫入TCNT就可以改變週期了
接著我再補充說明下pwm_config函式裡程式碼註釋關於自動載入怎麼回事？
定時器工作原理其實是TCNT的值在時鐘到來時，減一計數，每次減一完後，拿當前TCNT與TCMP比較，如果TCNT=TCMP，那麼訊號電平反向輸出，然後TCNT繼續減一計數，直到TCNT減到零後，如果有自動載入功能那麼此時將由TCNTB把計數初值再次寫給TCNTP，同時TCMPB把比較值給TCMP，這樣就完成一次初值重灌，然後繼續進行計數。我們給這種載入模式起了個名字叫雙緩衝機制，其中TCMPB和TCNTB就是Buffer快取。
前面說pwm.c集驅動和裝置於一體，那麼下面我們看看裝置相關的程式碼
注：kernel-3.0.8在/arch/plat-samsung/dev-pwm.c檔案中#define TIMER_RESOURCE_SIZE (1)
#define TIMER_RESOURCE(_tmr, _irq) \
(struct resource [TIMER_RESOURCE_SIZE]) { \
[0] = { \
.start = _irq, \
.end = _irq, \
.flags = IORESOURCE_IRQ \
} \
}
#define DEFINE_S3C_TIMER(_tmr_no, _irq) \
.name = "s3c24xx-pwm", \
.id = _tmr_no, \
.num_resources = TIMER_RESOURCE_SIZE, \
.resource = TIMER_RESOURCE(_tmr_no, _irq),\
/*
* since we already have an static mapping for the timer,
* we do not bother setting any IO resource for the base.
*/
struct platform_device s3c_device_timer[] = {
[0] = { DEFINE_S3C_TIMER(0, IRQ_TIMER0) },
[1] = { DEFINE_S3C_TIMER(1, IRQ_TIMER1) },
[2] = { DEFINE_S3C_TIMER(2, IRQ_TIMER2) },
[3] = { DEFINE_S3C_TIMER(3, IRQ_TIMER3) },
[4] = { DEFINE_S3C_TIMER(4, IRQ_TIMER4) },
};
EXPORT_SYMBOL(s3c_device_timer);
static struct platform_device *tq210_devices[] __initdata = {
...
#ifdef CONFIG_BACKLIGHT_PWM
&s3c_device_timer[0],
#endif
...
};三、Backlight核心驅動
程式碼/driver/video/backlight/backlight.c
核心中需要使能“Lowlevel Backlight controls”
Device Drivers --->
Graphics support --->
[*] Backlight & LCD device support --->
<*> Lowlevel Backlight controls程式碼分析
static int __init backlight_class_init(void)
{
backlight_class = class_create(THIS_MODULE, "backlight");//在/sys/class下注冊backlight類
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;//新增類屬性
backlight_class->suspend = backlight_suspend;
backlight_class->resume = backlight_resume;
return 0;
}backlight背光系統的主要就是靠這個類屬性，設定背光值就是向這個類屬性中某個成員寫入背光值，這個類屬性就是給使用者的同一介面
#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,
};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);//輸出最大亮度
}這個函式很簡單，但是重點是引入了幾個backlight背光子系統的幾個重要的資料結構，我們好好學習下。
首先是backlight背光子系統的裝置結構體backlight_device
struct backlight_device {
/* Backlight properties */
struct backlight_properties props;//背光屬性
/* 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;//背光操作函式，類似於file_operation
/* The framebuffer notifier block */
struct notifier_block fb_notif;
struct device dev;//內嵌裝置
};struct backlight_properties {
/* Current User requested brightness (0 - max_brightness) */
int brightness;//當前背光值
/* 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 */
};在看看背光操作函式
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 *);//更新背光狀態
/* Return the current backlight brightness (accounting for power,
fb_blank etc.) */
int (*get_brightness)(struct backlight_device *);//獲取背光值
/* 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 *);
};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;//傳入背光值
backlight_update_status(bd);//更新背光狀態
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);
}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); //註冊背光裝置
EXPORT_SYMBOL(backlight_device_unregister); //登出背光裝置四、基於PWM&Backlight的背光碟機動
結合上面的PWM核心層和Backlight背光子系統核心層，根據基於pwm的背光碟機動/driver/video/backlight/pwm_bl.c來修改成基於tq210的蜂鳴器驅動核心中需要使能“Generic PWM based Backlight Driver”
Device Drivers --->
Graphics support --->
[*] Backlight & LCD device support --->
<*> Generic PWM based Backlight Drivertq210蜂鳴器使用GPD0_1口，該埠工作在TOU0模式下，就可以通過裝置定時器的TCNT和TCMP來控制定時器的波形。
首先，在tq210的BSP檔案mach-tq210.c，如下新增
static struct platform_device tq210_backlight_device = {
.name = "pwm-backlight",//裝置名
.dev = {
.parent = &s3c_device_timer[0].dev,//該裝置基於pwm中的0號定時器
.platform_data = &tq_backlight_data,
},
};新增平臺數據
static struct platform_pwm_backlight_data tq210_backlight_data = {
.pwm_id = 0,//對應的就是Timer0
.max_brightness = 255,//最大亮度
.dft_brightness = 100,//255,//當前亮度
.lth_brightness = 50,//咱不知道幹啥用的
.pwm_period_ns = 20000,//78770,//T0，即輸出時鐘週期
.init = tq210_backlight_init,//埠初始化
.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));
}然後把tq210_backlight_device新增到tq210_devices陣列
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,//同時新增對應的s3c_device_timer[0]
#endif
...
};最後新增標頭檔案
#include <linux/pwm_backlight.h>static struct platform_driver pwm_backlight_driver = {
.driver = {
.name = "pwm-backlight", //驅動名需要與裝置名保持一致
.owner = THIS_MODULE,
},
.probe = pwm_backlight_probe,
.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);
}探測函式
static int pwm_backlight_probe(struct platform_device *pdev)
{
struct backlight_properties props;
struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
struct backlight_device *bl;
struct pwm_bl_data *pb; //本驅動的私有結構體
int ret;
if (!data) {
dev_err(&pdev->dev, "failed to find platform data\n");
return -EINVAL;
}
if (data->init) {//初始化埠，在BSP檔案中定義
ret = data->init(&pdev->dev);
if (ret < 0)
return ret;
}
pb = kzalloc(sizeof(*pb), GFP_KERNEL);
if (!pb) {
dev_err(&pdev->dev, "no memory for state\n");
ret = -ENOMEM;
goto err_alloc;
}
pb->period = data->pwm_period_ns;//獲取週期
pb->notify = data->notify;
pb->check_fb = data->check_fb;
pb->lth_brightness = data->lth_brightness *
(data->pwm_period_ns / data->max_brightness);
pb->dev = &pdev->dev;
pb->pwm = pwm_request(data->pwm_id, "backlight");//註冊pwm裝置
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");
memset(&props, 0, sizeof(struct backlight_properties));
props.type = BACKLIGHT_RAW;
props.max_brightness = data->max_brightness;
bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
&pwm_backlight_ops, &props);//註冊backlight裝置，注意pwm_backlight_ops函式
if (IS_ERR(bl)) {
dev_err(&pdev->dev, "failed to register backlight\n");
ret = PTR_ERR(bl);
goto err_bl;
}
bl->props.brightness = data->dft_brightness;
backlight_update_status(bl);//先點亮光
platform_set_drvdata(pdev, bl);//設定bl私有資料
return 0;
err_bl:
pwm_free(pb->pwm);
err_pwm:
kfree(pb);
err_alloc:
if (data->exit)
data->exit(&pdev->dev);
return ret;
}static const struct backlight_ops pwm_backlight_ops = {
.update_status = pwm_backlight_update_status,//更新背光亮度
.get_brightness = pwm_backlight_get_brightness,//獲取背光亮度
.check_fb = pwm_backlight_check_fb,
};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(pb->dev, brightness);
if (brightness == 0) {//背光值為0，關閉被背光
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
} else {//呼叫pwm中的API設定背光
brightness = pb->lth_brightness +
(brightness * (pb->period - pb->lth_brightness) / max);
pwm_config(pb->pwm, brightness, pb->period);
pwm_enable(pb->pwm);
}
return 0;
}五、測試
