OpenHarmony南向之PWM背光

概述

之前在讲《OpenHarmony南向之LCD显示屏》时，有提到显示屏的背光，但没有展开，今天我们来详细讲讲。

背光驱动模型也是基于HDF框架开发的，整个框架如下：

现在以RK3568为例，来看看PWM背光整个驱动，这里使用的是PWM占空比控制的背光，默认基于hdf的pwm驱动已经OK！

需要注意的是：这里是基于HDF实现的PWM和PWM背光，所以Linux内核里面原生的PWM和PWM背光相关配置需要关闭

hcs

device_info

display :: host {
    hostName = "display_host";

    device_pwm_bl :: device {
        device0 :: deviceNode {
            policy = 0;
            priority = 95;
            preload = 0;
            moduleName = "PWM_BL";
            deviceMatchAttr = "pwm_bl_dev";
        }
    }
    device_backlight :: device {
        device0 :: deviceNode {
            policy = 2;
            priority = 90;
            preload = 0;
            permission = 0660;
            moduleName = "HDF_BL";
            serviceName = "hdf_bl";
        }
    }
}

config

lcd_config.hcs

root {
    backlightConfig {
        pwmBacklightConfig {
            match_attr = "pwm_bl_dev";
            pwmDevNum = 1;
            pwmMaxPeriod = 25000;
            backlightDevName = "hdf_pwm";
            minBrightness = 0;
            defBrightness = 127;
            maxBrightness = 255;
        }
    }
}

源码分析

PWM_BL驱动

PWM_BL驱动(pwm_bl.c)加载后在初始化时主要做了如下几个工作：


//初始化相关PWM模块，主要包括打开相应pwm模块，从hcs获取pwm的配置，并更新配置，
//主要调用pwm相关的驱动接口，如PwmOpen，PwmSetConfig等
ret = BlPwmDevInit(object, blPwmDev);

//注册Backlight设备，具体实现在后面的HDF_BL驱动，这里最重要的就是注册的操作函数集 g_blDevOps，后面有展开 
blDev = RegisterBlDev(blPwmDev->name, &blPwmDev->props, &g_blDevOps, blPwmDev);

//更新Backlight状态
if (UpdateBacklightState(blDev, FB_POWER_ON) != HDF_SUCCESS) {
    HDF_LOGE("%s: UpdateBacklightState fail", __func__);
}

//更新Backlight亮度
if (UpdateBrightness(blDev, blPwmDev->props.defBrightness) != HDF_SUCCESS) {
    HDF_LOGE("%s: UpdateBrightness fail", __func__);
}

g_blDevOps函数集，里面只有一个更新亮度的操作函数，该函数会调用更底层的pwm的HDF驱动接口去更新PWM的占空比，从而控制背光的亮度，具体如下：

static int32_t BlPwmUpdateBrightness(struct BacklightDev *blDev, uint32_t brightness)
{
    int32_t ret;
    uint32_t duty;
    struct BlPwmDev *blPwmDev = NULL;

    blPwmDev = ToBlDevPriv(blDev);
    if (blPwmDev == NULL) {
        HDF_LOGE("%s blPwmDev is null", __func__);
        return HDF_FAILURE;
    }
    if (blPwmDev->props.maxBrightness == 0) {
        HDF_LOGE("%s maxBrightness is 0", __func__);
        return HDF_FAILURE;
    }
    if (brightness == 0) {
        return PwmDisable(blPwmDev->pwmHandle);
    }
    duty = (brightness * blPwmDev->config.period) / blPwmDev->props.maxBrightness;
    ret = PwmSetDuty(blPwmDev->pwmHandle, duty);
    if (ret != HDF_SUCCESS) {
        HDF_LOGE("%s: PwmSetDuty failed, ret %d", __func__, ret);
        return HDF_FAILURE;
    }
    return PwmEnable(blPwmDev->pwmHandle);
}

static struct BacklightOps g_blDevOps = {
    .updateBrightness = BlPwmUpdateBrightness,
};

HDF_BL驱动

HDF_BL驱动(hdf_bl.c)功能主要有2大块：

对外提供IoService的 Dispatch 接口
主要涉及到一些对外命令的处理，包括：

static BlCmdHandle g_blDevCmdHandle[] = {
     HdfGetMinBrightness,    /*获取最小亮度*/
     HdfGetCurrBrightness,   /*获取当前亮度*/
     HdfGetDefBrightness,    /*获取默认亮度*/
     HdfGetMaxBrightness,    /*获取最大亮度*/
     HdfGetBlDevList,        /*获取背光设备列表*/
     HdfSetBrightness,       /*设置亮度*/
 };