rpi - pwm_get() - how to use static lookup tables or device-tree

Question

I have a Raspberry Pi 3B with two motors on pwmchip0 (pwm0/pwm1). I successfully controlled the pwm-chip through sysfs, but now I want to put it inside a kernel module.

I saw <linux/pwm.h> and would like to use pwm_get(),pwm_put() and pwm_config(). I found this post and also dug through the examples on LXR, but it didn't quite help me. I am very new to device-trees and kernel programming in general. I am failing to request the pwm_device (ERR=1) but I can't figure out the problem.

• What do I have to specify for consumer_id?
• Do I even have to modify the device tree or add a static lookup table?
  • And if so how?

I have created a device tree overlay, but thant didn't work :/

/dts-v1/;
/include/ "bcm283x.dtsi"
/ {
        compatible = "brcm,bcm2708";
        motor-left-pwm {
                compatible = "motor-left";
                pwms = <&pwm 0 1000000 0>;
                pinctrl-names = "default";
        };
};

I tried adding a static lookup table:

static struct pwm_lookup crc_pwm_lookup[] = {
    PWM_LOOKUP("pwmchip0", 0, "0000:00:02.0", "pwm_left", 0>
    PWM_LOOKUP("pwmchip0", 1, "0000:00:02.0", "pwm_right", >
};

pwm_add_table(crc_pwm_lookup, ARRAY_SIZE(crc_pwm_lookup));

But ended up with this:

WARNING: "pwm_add_table" [/home/josh/drivers/motor/motor.ko] undefined!

insmod: ERROR: could not insert module /motor.ko: Unknown symbol in module

I read somewhere that means I cannot call this function :/

Answer 1

Yesss! Yesterday night I figured it out!

I guess I simply didn't understand the device tree and overlays at all. But I worked out this, with help of the pwm-2chan.dts:

/dts-v1/;
/plugin/;
/ {
        fragment@0 {
                target = <&soc>;
                __overlay__ {
                motorpwm {
                        compatible = "motor";
                        pwms = <&pwm 0 1000000>;
                        pinctrl-names = "default";
                        pinctrl-0 = <&pwm0_gpio18>;
                };
                };
        };

        fragment@1 {
                target = <&pwm>;
                frag1: __overlay__ {
                        status = "okay";
                };
        };
};

Then your driver will be probed:

static int my_probe(struct platform_device *pdev)
{
    printk("Probed");
    printk("Requesting PWM");
    pwm_left = pwm_get(&pdev->dev, NULL);
    if (IS_ERR(pwm_left)){
        printk("Requesting PWM failed %d", ERR_CAST(pwm_left));
        return -EIO;
    }
    printk("Requested PWM");
    return 0;
}

static int my_remove(struct platform_device *dev)
{
    printk("Removed");
    return 0;
}


static struct of_device_id my_match_table[] = {
     {
             .compatible = "motor",
     },
     {},
};
MODULE_DEVICE_TABLE(of, my_match_table);

static struct platform_driver my_platform_driver = {
    .probe = my_probe,
    .remove = my_remove,
    .driver = {
        .name = "motor",
        .owner = THIS_MODULE,
        .of_match_table = of_match_ptr(my_match_table),
    },
};