一般LCD的背光LED是通过PWM控制，调节PWM的占空比即可调整背光亮度。
比如S3C6410的GPF15，即PWM1，即可连接LCD的背光控制接口，进行背光控制。
其工作流程如下：
1）在linux中，通过控制sys目录参数修改背光，如：
/sys/devices/platform/s3c-lcd # echo 200 > backlight_level
2）该操作影响/driver/video/samsung/s3cfb.c中函数
static int s3cfb_sysfs_store_backlight_level(struct device *dev, struct device_attribute *attr, const char *buf, size_t len)
{
unsigned long value = simple_strtoul(buf, NULL, 10);
if (value < s3cfb_fimd.backlight_min || value > s3cfb_fimd.backlight_max)
return -ERANGE;
s3cfb_set_backlight_level(value);
return len;
}
3）s3cfb_set_backlight_level(value);同样位于/driver/video/samsung/s3cfb.c
static void s3cfb_set_backlight_level(int to)
{
s3cfb_fimd.backlight_level = to;
if (s3cfb_fimd.set_brightness)
(s3cfb_fimd.set_brightness)(to);
}
4）s3cfb_fimd.set_brightness是具体LCD对应参数的函数指针
一般位于/driver/video/samsung/your lcd.c (eg.s3cfb_lte480wv.c)
检查初始化LCD时是否有添加该参数，红色标注：
s3cfb_fimd.set_lcd_power = lcd_power_ctrl;
s3cfb_fimd.set_backlight_power = backlight_power_ctrl;
s3cfb_fimd.set_brightness = backlight_level_ctrl;
s3cfb_fimd.backlight_min = BACKLIGHT_LEVEL_MIN;
s3cfb_fimd.backlight_max = BACKLIGHT_LEVEL_MAX;
ok，上面的只是函数指针，接着在同文件中需要实现该函数：
void backlight_level_ctrl(s32 value)
{
if ((value < BACKLIGHT_LEVEL_MIN) || /* Invalid Value */
(value > BACKLIGHT_LEVEL_MAX) ||
(value == backlight_level)) /* Same Value */
return;
s3cfb_set_brightness((int)(value/3));
backlight_level = value;
}
5）s3cfb_set_brightness让我们又跳到了drivers/video/samsung/s3cfb_fimd4x.c中
注意这段需要PWM支持
void s3cfb_set_brightness(int val)
{
int channel = 1; /* must use channel-1 */
int usec = 0; /* don't care value */
unsigned long tcnt = 1000;
unsigned long tcmp = 0;
if (val < 0)
val = 0;
if (val > S3CFB_MAX_BRIGHTNESS)
val = S3CFB_MAX_BRIGHTNESS;
s3cfb_fimd.brightness = val;
tcmp = val * 5;
s3c6410_timer_setup (channel, usec, tcnt, tcmp);
}
6）channel1 即为PWM1，s3c6410_timer_setup函数位于arch/arm/plat-s3c64xx/pwm-s3c6410.c
tcnt 是PWM的周期
tcmp 是PWM的占空比
一下代码是PWM配置过程，精简过的代码便于阅读。
int s3c6410_timer_setup (int channel, int usec, unsigned long g_tcnt, unsigned long g_tcmp)
{
tcnt = 0xffffffff; /* default value for tcnt */
/* read the current timer configuration bits */
tcon = __raw_readl(S3C_TCON);
tcfg1 = __raw_readl(S3C_TCFG1);
tcfg0 = __raw_readl(S3C_TCFG0);
clk = clk_get(NULL, "timers");
if (IS_ERR(clk))
panic("failed to get clock for pwm timer");
clk_enable(clk);
pclk = clk_get_rate(clk);
/* configure clock tick */
switch(channel)
{
case 1:
/* set gpio as PWM TIMER1 to signal output*/
s3c_gpio_cfgpin(S3C64XX_GPF(15), S3C64XX_GPF15_PWM_TOUT1);
s3c_gpio_setpull(S3C64XX_GPF(15), S3C_GPIO_PULL_NONE);
tcfg1 &= ~S3C_TCFG1_MUX1_MASK;
tcfg1 |= S3C_TCFG1_MUX1_DIV2;
tcfg0 &= ~S3C_TCFG_PRESCALER0_MASK;
tcfg0 |= (PRESCALER) << S3C_TCFG_PRESCALER0_SHIFT;
tcon &= ~(7<<8);
tcon |= S3C_TCON_T1RELOAD;
break;
}
__raw_writel(tcfg1, S3C_TCFG1);
__raw_writel(tcfg0, S3C_TCFG0);
__raw_writel(tcon, S3C_TCON);
tcnt = 160;
__raw_writel(tcnt, S3C_TCNTB(channel));
tcmp = 110;
__raw_writel(tcmp, S3C_TCMPB(channel));
switch(channel)
{
case 1:
tcon |= S3C_TCON_T1MANUALUPD;
break;
}
__raw_writel(tcon, S3C_TCON);
tcnt = g_tcnt;
__raw_writel(tcnt, S3C_TCNTB(channel));
tcmp = g_tcmp;
__raw_writel(tcmp, S3C_TCMPB(channel));
/* start the timer running */
s3c6410_pwm_start ( channel);
return 0;
}
