Raspberry Pi serdev driver never reaches probe function-CodePudding

I want to write a minimal serdev Linux driver on a Raspberry Pi. Therefore I have to enable the kernel option SERIAL_DEV_CTRL_TTYPORT, but I don't know how. I have tried various options, but my Kernel Module never reaches the Probe function...

Here is what I got already:

I tried to enable the option by changing the /boot/cmdline.txt to:

SERIAL_DEV_CTRL_TTYPORT SERIAL_DEV_CTRL_TTYPORT=y SERIAL_DEV_CTRL_TTYPORT=yes root=PARTUUID=8d696e29-02 rootfstype=ext4 fsck.repair=yes rootwait modules-load=dwc2,g_ether

The device tree overlay:

/dts-v1/;
/plugin/;
/ {
        compatible = "brcm,bcm2835";
        fragment@0 {
                target = <&uart0>;
                status = "okay";
                __overlay__ {
                        my_device {
                                compatible = "brightlight,echodev";
                                status = "okay";
                        };
                };
        };
};

The Kernel Module:

#include <linux/module.h>
#include <linux/init.h>
#include <linux/serdev.h>
#include <linux/mod_devicetable.h>
#include <linux/property.h>
#include <linux/platform_device.h>
#include <linux/of_device.h>

/* Meta Information */
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Johannes 4 GNU/Linux");
MODULE_DESCRIPTION("A simple serdev example");

/* Declate the probe and remove functions */
static int dt_probe(struct serdev_device *serdev);
static void dt_remove(struct serdev_device *serdev);

static struct of_device_id my_driver_ids[] = {
        {
                .compatible = "brightlight,echodev",
        }, { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, my_driver_ids);

static struct serdev_device_driver my_driver = {
        .probe = dt_probe,
        .remove = dt_remove,
        .driver = {
                .name = "echodev",
                .of_match_table = my_driver_ids,
        },
};

/**
 * @brief This function is called on loading the driver
 */
static int dt_probe(struct serdev_device *serdev) {
        printk("my_serdev - Now I am in the probe function!");
        return 0;
}

/**
 * @brief This function is called on unloading the driver
 */
static void dt_remove(struct serdev_device *serdev) {
        printk("my_serdev - Now I am in the remove function\n");
}

module_serdev_device_driver(my_driver);

Do you have any tips?

UPDATE 1:

I checked my Kernel .config file and found out, that CONFIG_SERIAL_DEV_CTRL_TTYPORT is already set and enabled. I double checked it with

pi@raspberrypi:~ $ sudo modprobe configs
pi@raspberrypi:~ $ gzip -d /proc/config.gz --stdout | grep SERIAL_DEV
CONFIG_SERIAL_DEV_BUS=y
CONFIG_SERIAL_DEV_CTRL_TTYPORT=y

But then, why does my module never reaches the probe function???

Best regards, Johannes

CodePudding user response：

Ok, I got it, but I don't know exactly why it is working know.

When posting this example, I used dtoverlay to load the device tree overlay:

sudo dtoverlay testoverlay.dtbo

When doing so, I couldn't reach the probe function. Then I copied my overlay to /boot/overlays and added it to /boot/config.txt:

dtoverlay=testoverlay

And after a reboot, I inserted my kernel module and it reached the probe function. Does anyone know why this works now but not before?