PWM Use

Firefly-RK3128 development board has 4 PWMs, namely PWM0 ~ PWM3:

PWM0/GPIO0_D2: exported in the extension board

PWM1/GPIO0_D3: used as AUX_DET signal internally

PWM2/GPIO0_D4: used as RTC_INT signal internally

PWM3: used by infrared transceivers

This chapter mainly describes how to configure PWM. The PWM driver of
Firefly-RK3128 is:

   kernel/drivers/pwm/pwm-rockchip.c

Configuration steps

Configuration of PWM mainly includes the following three steps:
configure PWM DTS nodes, configure PWM kernel driver, and control PWM
device.

Create PWM DTS Node

The following PWM nodes are defined in
kernel/arch/arm/boot/dts/rk312x.dtsi, as shown below:

   pwm0: pwm@20050000 {
   	compatible = "rockchip,rk-pwm";
   	reg = <0x20050000 0x10>;
   	#pwm-cells = <2>;
   	pinctrl-names = "default";
   	pinctrl-0 = <&pwm0_pin>;
   	clocks = <&clk_gates7 10>;
   	clock-names = "pclk_pwm";
   	status = "disabled";
   };

    pwm1: pwm@20050010 {
        compatible = "rockchip,rk-pwm";
        reg = <0x20050010 0x10>;
        #pwm-cells = <2>;
        pinctrl-names = "default";
        pinctrl-0 = <&pwm1_pin>;
        clocks = <&clk_gates7 10>;
        clock-names = "pclk_pwm";
        status = "disabled";
    };

    pwm2: pwm@20050020 {
         compatible = "rockchip,rk-pwm";
         reg = <0x20050020 0x10>;
         #pwm-cells = <2>;
         pinctrl-names = "default";
         pinctrl-0 = <&pwm2_pin>;
         clocks = <&clk_gates7 10>;
         clock-names = "pclk_pwm";
         status = "disabled";
    };

    pwm3: pwm@20050030 {
          compatible = "rockchip,rk-pwm";
          reg = <0x20050030 0x10>;
          #pwm-cells = <2>;
          pinctrl-names = "default";
          pinctrl-0 = <&pwm3_pin>;
          clocks = <&clk_gates7 10>;
          clock-names = "pclk_pwm";
          status = "disabled";
    };

To use PWM0, you need to add to file
kernel/arch/arm/boot/dts/rk3128-fireprime.dts:

   &pwm0 {
          status = "okay";
   };

Configure PWM kernel driver

The PWM driver is in file kernel/drivers/pwm/pwm-rockchip.c

Control PWM Device

Now you can use the PWM node created above to control devices, as
shown in the following steps:

(1). Include the following header file into the device driver files to
be controlled by PWM:

   #include <linux/pwm.h>

This header file mainly includes PWM function interface.

(2). Request for PWM

You can use the pwm_request function to request the PWM device. For
example:

   struct pwm_device * pwm0=NULL;pwm0= pwm_request(0, “backlight-pwm”);

See The API of PWM device for more detail of this function.

(3). Configure PWM

You can use the function pwm_config to set the PWM configuration. For
example:

   pwm_config(pwm0, 500000, 1000000)；

See The API of PWM device for more detail of this function.

(4). PWM enabling function

Then you start the pwm device using the pwm_enable function. For
example：

   int pwm_enable(struct pwm_device *pwm);

See The API of PWM device for more detail of this function.

The API of PWM device

   /**
    * pwm_request() - request a PWM device
    * @pwm_id: global PWM device index
    * @label: PWM device label
    *
    * This function is deprecated, use pwm_get() instead.
    */
    struct pwm_device *pwm_request(int pwm_id, const char *label);


   /**
    * pwm_free() - free a PWM device
    * @pwm: PWM device
    *
    * This function is deprecated, use pwm_put() instead.
    */
    void pwm_free(struct pwm_device *pwm);


   /**
    * pwm_config() - change a PWM device configuration
    * @pwm: PWM device
    * @duty_ns: "on" time (in nanoseconds)
    * @period_ns: duration (in nanoseconds) of one cycle
    */
    int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);


   /**
    * pwm_enable() - start a PWM output toggling
    * @pwm: PWM device
    */
    int pwm_enable(struct pwm_device *pwm);


   /**
    * pwm_disable() - stop a PWM output toggling
    * @pwm: PWM device
    */
    void pwm_disable(struct pwm_device *pwm);