背光配置

如果没有调节背光亮度需求，仅仅是亮或黑屏，则用 GPIO 控制较为简单，只需要在 panel 节点中一个地方配置好就可以，如下；

panel_xxx {
    compatible = "artinchip,aic-general-lvds-panel";
    status = "okay";

    enable-gpios = <&gpio_c 7 GPIO_ACTIVE_HIGH>; //背光控制引脚，须和原理图一致
    port {
        panel_lvds_in: endpoint {
            remote-endpoint = <&lvds0_out>;
        };
};

PWM 控制背光

如果有调节背光亮度的需求，则需要使用 PWM 来控制背光，有以下步骤配置：

board.dts panel 节点中需添加 backlight 节点，如下：

panel_xxx {
    compatible = "artinchip,aic-general-lvds-panel";
    status = "okay";

    //enable-gpios = <&gpio_c 7 GPIO_ACTIVE_HIGH>;
    backlight = <&backlight>;//添加 backlight
    port {
        panel_lvds_in: endpoint {
            remote-endpoint = <&lvds0_out>;
        };
};

board.dts 中使能 backlight 节点

backlight: backlight {
     compatible = "pwm-backlight";
     /* pwm node name; pwm device No.; period_ns; pwm_polarity */
     pwms = <&pwm 0 1000000 0>; //硬件对应的哪一路 PWM 接口，需要和原理图确认
     brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>; //每一级对应的占空百分比
     default-brightness-level = <6>;
     status = "okay";
};

board.dts 中使能对应的 PWM

&pwm {
    status = "okay";    //PWM 节点总开关
    pinctrl-names = "default";
    pinctrl-0 = <&pwm0_pins_d>;    //添加背光控制 pinmux 引脚
    /* mode: up-count, down-count, up-down-count
       action: none, low, high, inverse */
    pwm0 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        aic,rise-edge-delay = <10>;
        aic,fall-edge-delay = <10>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "low", "none", "high";
        aic,action1 = "none", "none", "none", "high", "none", "low";
        status = "okay";    //使能硬件对应那一路的 PWM 子节点
    };
    ......
};

board-u-boot.dtsi 添加对应的 PWM 节点

/ {
    ......
    backlight: backlight {
        u-boot,dm-pre-reloc;
    };
};

&pwm {
    u-boot,dm-pre-reloc;
    pwm0 {
        u-boot,dm-pre-reloc;
    };
    ......
};

&pinctrl {
    ......
    pwm0_pins_d: pwm0-3 {
        u-boot,dm-pre-reloc;
        pins {
            u-boot,dm-pre-reloc;
        };
    };
    ......
};

确认内核中打开如下配置

CONFIG_PWM=y
CONFIG_PWM_ARTINCHIP=y
CONFIG_BACKLIGHT_PWM=y

确认 uboot 中打开如下配置

CONFIG_PWM_ARTINCHIP=y
CONFIG_BACKLIGHT_PWM=y

PWM 背光测试调试

确认硬件信号的连通性
查看启动 log 是否有异常

查看如下命令节点是否存在，并通过命令调节背光或测试 PWM 输出信号

echo 5 > /sys/class/backlight/backlight/brightness //设置 brightness 级数, 对应到 backlight 节点设置的占空百分比。