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PWM 配置

内核配置

在 Luban 根目录下执行 make kernel-menuconfig，进入 kernel 的功能配置，按如下选择：

Linux
    Device Drivers  --->
        [*] Pulse-Width Modulation (PWM) Support  --->
            <*>   ArtInChip PWM support
            <*>   ArtInChip EPWM support

通常，PWM 模块被用于 背光控制功能，以下是打开 Linux 中背光控制模块的方法：

Linux
    Device Drivers  --->
        Graphics support  --->
            Backlight & LCD device support  --->
                <*> Lowlevel Backlight controls
                <*>   Generic PWM based Backlight Driver

当使用 logo 功能时，在 Boot 阶段也需要打开屏幕的背光。在 Boot 中打开背光控制模块的方法（在 luban 根目录下执行 make bm/boot-menuconfig）：

U-Boot
    Device Drivers  --->
        [*] Enable support for pulse-width modulation devices (PWM)
        [*]   Enable support for ArtInChip PWM
        Graphics support  --->
            [*] Generic PWM based Backlight Driver

DTS 参数配置

PWM 驱动支持从 DTS 中配置的自定义参数，如下表：

表 1. PWM 自定义参数
参数名称 类型 取值范围 功能说明
mode 字符串 up/down/up-down-count 配置增减模式
tb-clk-rate 正整数 (0, 24000000) 时基计数器的工作时钟
action0 字符串 none/low/high/inverse 多个关键时点的触发行为
action1 字符串 none/low/high/inverse 多个关键时点的触发行为
default-level 正整数 [0, 1] 默认/初始电平
注：

表中为了更加简洁，参数名称都省略了前缀“aic,”。

表中 action0 和 action1 四种取值的含义，定义如下：

表 2. action0 和 action1 取值含义
Action 类型 行为描述
none 不做任何变化，保持之前的输出电平
low 跳变为 0 电平
high 跳变为 1 电平
inverse 跳变为反向的电平，比如从 0 跳变为 1

时钟配置

PWM 模块涉及时钟的衍生关系：

../images/pwm_clk_tree.png
图 1. PWM 模块的时钟衍生关系图

EWM 模块涉及时钟的衍生关系：

../images/epwm_clk_tree.png
图 2. EPWM 模块的时钟衍生关系图

其中，前两个时钟在 PWM 控制器的节点中配置，后两个时钟在 Board 中的 PWM 子节点（对应通道）中配置。

注：
容易混淆的 sysclk：

  • PWM 驱动中，按照惯例将父时钟称作 sysclk，即上图的 PLL INT1；

  • PWM 硬件 spec 中，将上图中的 PWM Clk 称作 sysclk。

D211 配置

common/d211.dtsi 中的参数配置：

pwm:pwm@19240000{compatible="artinchip,aic-pwm-v1.0";reg=<0x00x192400000x00x1000>;interrupts-extended=<&plic090IRQ_TYPE_LEVEL_HIGH>;#pwm-cells = <3>;clocks=<&cmuCLK_PWM>,<&cmuCLK_PLL_INT1>;clock-names="pwm","sysclk";resets=<&rstRESET_PWM>;clock-rate=<48000000>;};epwm:epwm@18200000{compatible="artinchip,aic-epwm-v1.0";reg=<0x00x182000000x00x600>,<00x1820F0000x00x1000>;interrupts-extended=<&plic025IRQ_TYPE_LEVEL_HIGH>;#pwm-cells = <3>;clocks=<&cmuCLK_PWMCS>,<&cmuCLK_PLL_INT1>;clock-names="pwmcs","sysclk";resets=<&rstRESET_PWMCS>;clock-rate=<48000000>;status="disabled";};

Board 配置

  • PWM 通道配置
    xxx/board.dts 中的参数配置：
    &pwm {
    status = "okay";
    pinctrl-names = "default";
    pinctrl-0 = <&pwm2_pins_b>;
    /* 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 = "disabled";
    };

    pwm1 {
        aic,mode = "down-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 = "disabled";
    };

    pwm2 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "low", "none";
        aic,action1 = "none", "none", "none", "low", "high", "none";
        aic,default-level = <0>;
        aic,rise-edge-delay = <10>;
        aic,fall-edge-delay = <10>;
        status = "okay";
    };

    pwm3 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "low", "high", "none";
        aic,action1 = "none", "none", "none", "high", "low", "none";
        aic,rise-edge-delay = <10>;
        aic,fall-edge-delay = <10>;
        status = "disabled";
    };
};

&epwm {
    status = "disabled";
    pinctrl-names = "default";
    pinctrl-0 = <&epwm0_pins_a>,
             <&epwm1_pins_a>,
             <&epwm2_pins_a>;
    /* mode: up-count, down-count, up-down-count
    action: none, low, high, inverse */
    epwm0 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };

    epwm1 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };

    epwm2 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };

    epwm3 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };

    epwm4 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };

    epwm5 {
        aic,mode = "up-count";
        aic,tb-clk-rate = <24000000>;
        /*            CBD,    CBU,    CAD,    CAU,    PRD,   ZRO */
        aic,action0 = "none", "none", "none", "high", "none", "low";
        aic,action1 = "none", "high", "none", "none", "none", "low";
        status = "disabled";
    };
};
  • 背光控制配置
    需要在 xxx/board.dts 中新增一个 backlight 节点，如下：
    backlight: backlight {
    compatible = "pwm-backlight";
    /* pwm node name; pwm device No.; period_ns; pwm_polarity */
    pwms = <&pwm 2 1000000 0>;
    brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
    default-brightness-level = <8>;
    status = "okay";
};

    其中 “&pwm 2” 表示要使用 pwm2 通道作为背光控制用（要确认和硬件上的电路连接是一致的）。

    在屏幕 panel 节点中，需要引用 backlight：
    panel_lvds {
    compatible = "artinchip,aic-general-lvds-panel";
    data-mapping = "vesa-24";
    data-channel = "single-link1";
    backlight = <&backlight>;
    status = "okay";
    ...
};