7.8.2. 参数配置
7.8.2.1. 内核配置
参考快速入门 - 编译概述 - Kernel配置，进入kernel的功能配置，按如下选择：
Linux
Device Drivers --->
[*] Pulse-Width Modulation (PWM) Support --->
<*> ZX PWM 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boot logo功能时，在U-Boot阶段也需要打开屏幕的背光。在U-Boot中打开背光控制模块的方法（参考快速入门 - 编译概述 - Bootloader配置）：
U-Boot
Device Drivers --->
[*] Enable support for pulse-width modulation devices (PWM)
[*] Enable support for ZX PWM
Graphics support --->
[*] Generic PWM based Backlight Driver
7.8.2.2. DTS 参数配置
7.8.2.2.1. PWM 自定义参数
PWM驱动支持从DTS中配置的自定义参数，如下表：
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 |
注意，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：
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，比如原本是0则跳变为1 |
7.8.2.2.2. 时钟配置
PWM模块涉及4个时钟的衍生关系：
图 7.36 PWM 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。
备注
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。
7.8.2.2.3. M4 配置
common/m4.dtsi中的参数配置：
pwm: pwm@19240000 {
compatible = "zx,aic-pwm-v1.0";
reg = <0x0 0x19240000 0x0 0x1000>;
interrupts-extended = <&plic0 90 IRQ_TYPE_LEVEL_HIGH>;
#pwm-cells = <3>;
clocks = <&cmu CLK_PWM>, <&cmu CLK_PLL_INT1>;
clock-names = "pwm", "sysclk";
resets = <&rst RESET_PWM>;
clock-rate = <48000000>;
};
7.8.2.2.4. Board 配置
7.8.2.2.4.1. 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";
};
};
7.8.2.2.4.2. 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 = "zx,aic-general-lvds-panel";
data-mapping = "vesa-24";
data-channel = "single-link1";
backlight = <&backlight>;
status = "okay";
...
};