pwm驱动 pca9685 代码简析

pwm驱动十分常见，这篇博文就以pca9685为例，简单分析一下pwm驱动的常用套路，本文注重重代码逻辑，轻寄存器hack，寄存器hack，请参考datasheet。

代码解析

源码路径drivers/pwm/pwm-pca9685.c

首先看驱动的probe函数

static int pca9685_pwm_probe(struct i2c_client *client,const struct i2c_device_id *id)
{struct pca9685 *pca;//驱动结构体pcaint ret;int mode2;pca = devm_kzalloc(&client->dev, sizeof(*pca), GFP_KERNEL);//动态分配if (!pca)return -ENOMEM;pca->regmap = devm_regmap_init_i2c(client, &pca9685_regmap_i2c_config);//regmap初始化if (IS_ERR(pca->regmap)) {ret = PTR_ERR(pca->regmap);dev_err(&client->dev, "Failed to initialize register map: %d\n",ret);return ret;}pca->duty_ns = 0;pca->period_ns = PCA9685_DEFAULT_PERIOD;//默认值 5000000nsi2c_set_clientdata(client, pca); // client->dev.drvdata = pca;regmap_read(pca->regmap, PCA9685_MODE2, &mode2); //读取mode2寄存器if (device_property_read_bool(&client->dev, "invert"))//读取设备树，配置mode2寄存器。mode2 |= MODE2_INVRT;elsemode2 &= ~MODE2_INVRT;if (device_property_read_bool(&client->dev, "open-drain"))mode2 &= ~MODE2_OUTDRV;elsemode2 |= MODE2_OUTDRV;regmap_write(pca->regmap, PCA9685_MODE2, mode2);//设置mode2寄存器/* clear all "full off" bits */regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);//LED清零regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, 0);pca->chip.ops = &pca9685_pwm_ops;        //设置pwm回调函数/* add an extra channel for ALL_LED */pca->chip.npwm = PCA9685_MAXCHAN + 1;    //设置pwm数量pca->chip.dev = &client->dev;pca->chip.base = -1;ret = pwmchip_add(&pca->chip);           //向pwm子系统注册当前pwm chipif (ret < 0)return ret;ret = pca9685_pwm_gpio_probe(pca);       //gpio初始化相关if (ret < 0) {pwmchip_remove(&pca->chip);return ret;}/* the chip comes out of power-up in the active state */pm_runtime_set_active(&client->dev);    //电源管理pm open/** enable will put the chip into suspend, which is what we* want as all outputs are disabled at this point*/pm_runtime_enable(&client->dev);        //电源管理pm enablereturn 0;
}

probe函数主要做了:

1.驱动结构体pca的动态分配，初始化。

2.regmap的初始化，用于提供读写i2c寄存器的底层接口。

3.芯片初始化的一些寄存器配置。

4.pwm回调函数注册。

5.gpio回调函数注册。

6.电源管理初始化。

编写pwm驱动，最核心的就是编写pwm_ops回调函数，这些回调函数会在，sys文件系统的相应文件读写时，被pwm子系统调用，让我们来看看：

默认echo路径：

/sys/class/pwm/pwmchipX/pwmX

static const struct pwm_ops pca9685_pwm_ops = { //pwm ops回调.enable = pca9685_pwm_enable,     //echo 1 >enable时调用.disable = pca9685_pwm_disable,   //echo 0 > enable时调用 .config = pca9685_pwm_config,     //echo xx >period; echo xx > duty_cycle时调用.request = pca9685_pwm_request,   //echo xx > export时调用.free = pca9685_pwm_free,         //echo xx >  unexport时调用.owner = THIS_MODULE,
};

pca9685_pwm_config回调函数是这个pwm驱动的核心，用于配置pwm的周期，占空比，简单注释一下。

static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,//pwm 配置int duty_ns, int period_ns)
{struct pca9685 *pca = to_pca(chip);unsigned long long duty;unsigned int reg;int prescale;if (period_ns != pca->period_ns) {//设置新的pwm周期prescale = DIV_ROUND_CLOSEST(PCA9685_OSC_CLOCK_MHZ * period_ns,//通过新的周期，算出prescalePCA9685_COUNTER_RANGE * 1000) - 1;if (prescale >= PCA9685_PRESCALE_MIN &&prescale <= PCA9685_PRESCALE_MAX) {/** putting the chip briefly into SLEEP mode* at this point won't interfere with the* pm_runtime framework, because the pm_runtime* state is guaranteed active here.*//* Put chip into sleep mode */pca9685_set_sleep_mode(pca, true);//设置为sleep mode/* Change the chip-wide output frequency */regmap_write(pca->regmap, PCA9685_PRESCALE, prescale);//设置除数/* Wake the chip up */pca9685_set_sleep_mode(pca, false);//wakeuppca->period_ns = period_ns;//新周期设置完成} else {dev_err(chip->dev,"prescaler not set: period out of bounds!\n");return -EINVAL;}}pca->duty_ns = duty_ns;//设置duty时间(一个周期内pwm为高的时间)if (duty_ns < 1) {if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_H;elsereg = LED_N_OFF_H(pwm->hwpwm);regmap_write(pca->regmap, reg, LED_FULL);//小于1ns，就认为输出一直为低return 0;}if (duty_ns == period_ns) {//如果两个时间相同,就认为是一直为高电平/* Clear both OFF registers */if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_L;elsereg = LED_N_OFF_L(pwm->hwpwm);regmap_write(pca->regmap, reg, 0x0);//full off 位清零if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_H;elsereg = LED_N_OFF_H(pwm->hwpwm);regmap_write(pca->regmap, reg, 0x0);/* Set the full ON bit */if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_ON_H;elsereg = LED_N_ON_H(pwm->hwpwm);regmap_write(pca->regmap, reg, LED_FULL);//full on位 置1return 0;}duty = PCA9685_COUNTER_RANGE * (unsigned long long)duty_ns;duty = DIV_ROUND_UP_ULL(duty, period_ns);//计算占空比 duty = (duty/period) * 4096 if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_L;elsereg = LED_N_OFF_L(pwm->hwpwm);regmap_write(pca->regmap, reg, (int)duty & 0xff);//设置占空比if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_H;elsereg = LED_N_OFF_H(pwm->hwpwm);regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);//设置占空比的高4位/* Clear the full ON bit, otherwise the set OFF time has no effect */if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_ON_H;elsereg = LED_N_ON_H(pwm->hwpwm);regmap_write(pca->regmap, reg, 0);//full on 位清零，这样pwm才会生效return 0;
}

其他pwm回调函数的简单注释：

static int pca9685_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
{struct pca9685 *pca = to_pca(chip);//获得pca驱动结构体unsigned int reg;/** The PWM subsystem does not support a pre-delay.* So, set the ON-timeout to 0*/if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_ON_L;elsereg = LED_N_ON_L(pwm->hwpwm);regmap_write(pca->regmap, reg, 0);//清除LED_ON_L寄存器if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_ON_H;elsereg = LED_N_ON_H(pwm->hwpwm);regmap_write(pca->regmap, reg, 0);//清除LED_ON_H寄存器,led full on/** Clear the full-off bit.* It has precedence over the others and must be off.*/if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_H;elsereg = LED_N_OFF_H(pwm->hwpwm);//清除LED_OFF寄存器full off位regmap_update_bits(pca->regmap, reg, LED_FULL, 0x0);//return 0;
}static void pca9685_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
{struct pca9685 *pca = to_pca(chip);//获得pca驱动结构体unsigned int reg;if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_H;elsereg = LED_N_OFF_H(pwm->hwpwm);regmap_write(pca->regmap, reg, LED_FULL);//led off full位置1，所有输出禁能。/* Clear the LED_OFF counter. */if (pwm->hwpwm >= PCA9685_MAXCHAN)reg = PCA9685_ALL_LED_OFF_L;elsereg = LED_N_OFF_L(pwm->hwpwm);regmap_write(pca->regmap, reg, 0x0);//
}static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
{struct pca9685 *pca = to_pca(chip);//获得pca驱动结构体if (pca9685_pwm_is_gpio(pca, pwm))//判断该port是否用作gpio, 如果用作gpio，则不能再申请该port作为pwm。return -EBUSY;pm_runtime_get_sync(chip->dev);//电源管理引用计数加1return 0;
}static void pca9685_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
{pca9685_pwm_disable(chip, pwm);//pwm禁能pm_runtime_put(chip->dev);//电源管理引用计数减1
}

电源管理的回调函数：

static void pca9685_set_sleep_mode(struct pca9685 *pca, bool enable)
{regmap_update_bits(pca->regmap, PCA9685_MODE1,//设置寄存器位MODE1_SLEEPMODE1_SLEEP, enable ? MODE1_SLEEP : 0);if (!enable) {/* Wait 500us for the oscillator to be back up */udelay(500);}
}static int pca9685_pwm_runtime_suspend(struct device *dev)//进入休眠时调用
{struct i2c_client *client = to_i2c_client(dev);struct pca9685 *pca = i2c_get_clientdata(client);pca9685_set_sleep_mode(pca, true);//芯片进入休眠return 0;
}static int pca9685_pwm_runtime_resume(struct device *dev)//从休眠恢复时调用
{struct i2c_client *client = to_i2c_client(dev);struct pca9685 *pca = i2c_get_clientdata(client);pca9685_set_sleep_mode(pca, false);//芯片唤醒return 0;
}static const struct dev_pm_ops pca9685_pwm_pm = {SET_RUNTIME_PM_OPS(pca9685_pwm_runtime_suspend,pca9685_pwm_runtime_resume, NULL)
};

gpio相关的配置暂不分析了。

简单总结一下

写pwm驱动的核心套路，那就是pwm_ops回调函数的编写。

主要实现底层功能：配置pwm周期，使能pwm，禁能pwm，即可。其他事情pwm子系统已经帮我们完成了。

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pwm驱动 pca9685 代码简析

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