RK3568笔记四十七：PWM 子系统

news2025/1/17 3:13:27

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pwm 子系统功能单一，很少单独使用，一般用于控制显示屏的背光、控制无源蜂鸣器、伺服电机、电压调节等等。

一、PWM介绍

PWM(Pulse width modulation)，脉冲宽度调制。在内核中 PWM 驱动较简单，但是麻雀虽小，五脏俱全，基本的框架是完整的。

pwm 控制器驱动 soc 厂商已经写好，我们要做的是在设备树 (或者是设备树插件) 中开启控制器节点，描述 pwm 设备节点，然后驱动中调用内核 PWM 提供的接口，来实现 pwm 驱动控制。

二、硬件原理图

PWM 通道与引脚

这里使用GPIO0_C7引脚，复用为pwm功能。

三、设备树修改

修改/home/alientek/rk3568_linux_sdk/kernel/arch/arm64/boot/dts/rockchip/rk3568-atk-evb1-ddr4- v10.dtsi 文件


&pwm0 {
    status = "okay";
    pinctrl-names = "active";
    pinctrl-0 = <&pwm0m1_pins>;
};


&{/} {
    pwm_demo: pwm_demo {
        status = "okay";
        compatible = "pwm_demo";

        back {
            pwm-names = "pwm-demo";
            pwms = <&pwm0 0 10000 1>;
            duty_ns = <5000>;
        };
    };
};

重新编译内核，烧写boot.img文件。

四、驱动

pwm_drv.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/of_platform.h>
#include <linux/leds.h>
#include <linux/err.h>
#include <linux/pwm.h>
#include <linux/leds_pwm.h>
#include <linux/slab.h>

struct pwm_device	*pwm_demo;  //定义pwm设备结构体

/*简单驱动*/
static int pwm_demo_probe(struct platform_device *pdev)
{
	int ret = 0;
	struct device *dev = &pdev->dev;
	struct device_node *child; // 保存子节点
	printk("match success \n");

	child = of_get_next_child(dev->of_node, NULL);
	if (child)
	{
		pwm_demo = devm_of_pwm_get(dev, child, NULL);
		if (IS_ERR(pwm_demo)) 
		{
			printk(KERN_ERR" pwm_demo，get pwm error!!\n");
			return -1;
		}
	}
	else
	{
		printk(KERN_ERR" pwm_demoof_get_next_child error!!\n");
		return -1;
	}

	/*配置频率100KHz 占空比80%*/
	pwm_config(pwm_demo, 1000, 5000);
	/*反相 频率100KHz 占空比20%*/
	pwm_set_polarity(pwm_demo, PWM_POLARITY_INVERSED);
	pwm_enable(pwm_demo);

	return ret;
}

static int pwm_demo_remove(struct platform_device *pdev)
{
	pwm_config(pwm_demo, 0, 5000);
    pwm_free(pwm_demo);
	return 0;
}

static const struct of_device_id of_pwm_leds_match[] = {
	{.compatible = "rockchip,rk3568-pwm",},
	{},
};

static struct platform_driver pwm_demo_driver = {
	.probe		= pwm_demo_probe,
	.remove		= pwm_demo_remove,
	.driver		= {
		.name	= "rockchip,rk3568-pwm",
		.of_match_table = of_pwm_leds_match,
	},
};

module_platform_driver(pwm_demo_driver);

MODULE_AUTHOR("yifeng");
MODULE_DESCRIPTION("PWM DEMO driver");
MODULE_LICENSE("GPL v2");

makefile

KERNELDIR := /home/alientek/rk3568_linux_sdk/kernel
ARCH=arm64
CROSS_COMPILE=/opt/atk-dlrk356x-toolchain/usr/bin/aarch64-buildroot-linux-gnu-

export  ARCH  CROSS_COMPILE

CURRENT_PATH := $(shell pwd)
obj-m := pwm_drv.o

build: kernel_modules

kernel_modules:
	$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modules
clean:
	$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean