设计说明

PWM 驱动的初始化过程见 aic_pwm_probe()函数，除了普通 platform 设备的处理过程（申请 regs 资源、clk、reset）外，需要调用 PWM 子系统的接口 pwmchip_add()来注册一个 PWM 控制器。

int pwmchip_add(struct pwm_chip *chip);

其中参数 chip 中关键信息有：通道数目、PWM 控制器的 ops 等，aic_pwm_ops 定义如下：

static const struct pwm_ops aic_pwm_ops = {
    .free = aic_pwm_free,
    .get_state = aic_pwm_get_state,
    .config = aic_pwm_config,
    .set_polarity = aic_pwm_set_polarity,
    .enable = aic_pwm_enable,
    .disable = aic_pwm_disable,
    .owner = THIS_MODULE,
};

在 中，我们打开了一个背光设备“Generic PWM based Backlight Driver”，这个设备对应的驱动代码见 drivers/video/backlight/pwm_bl.c，在其中的 probe()函数中会调用 devm_pwm_get()来获取对应的 pwm 设备。

pwm_bl.c, pwm_backlight_probe()
    -> pwm/core.c, devm_pwm_get()
        -> aic_pwm_get_state()
    -> pwm/core.c, pwm_apply_state()
        -> aic_pwm_config()
        -> aic_pwm_set_polarity()

PWM 的中断处理函数暂时为空，还不确定有哪些异常需要处理。

struct aic_pwm_arg {
    bool available;
    enum aic_pwm_mode mode;
    u32 tb_clk_rate;
    u32 freq;
    u32 db_red; /* Rising edge delay count of Dead-band */
    u32 db_fed; /* Failing edge delay count of Dead-band */
    struct aic_pwm_action action0;
    struct aic_pwm_action action1;
    u32 period;
    bool def_level;
    enum pwm_polarity polarity;
};

struct aic_pwm_chip {
    struct pwm_chip chip;
    struct attribute_group attrs;
    struct aic_pwm_arg args[AIC_PWM_CH_NUM];
    unsigned long pll_rate;
    unsigned long clk_rate;
    void __iomem *regs;
    struct clk *clk;
    struct reset_control *rst;
    u32 irq;
};

struct aic_pwm_action {
    enum aic_pwm_action_type CBD;
    enum aic_pwm_action_type CBU;
    enum aic_pwm_action_type CAD;
    enum aic_pwm_action_type CAU;
    enum aic_pwm_action_type PRD;
    enum aic_pwm_action_type ZRO;
};