Question

I am writing a driver for the GPIO pins on an ARM platform.
My driver works correctly and I’ve avoided the problem until
now by manually mknod’ing a device file.

my initialization code:


static int __init gpio_init (void)
{

    void *ptr_error;
    if (register_chrdev(249, "gpio_device", &fops) < 0){
            printk(KERN_INFO "Registering device failed\n");
            return -EINVAL;
    }

    if ((device_class = class_create(THIS_MODULE, "gpio_device"))
                                                    == NULL){
            unregister_chrdev_region(DEV_T, 1);
            printk(KERN_INFO "Class creation failed\n");
            return -EINVAL;
    }
    ptr_error = device_create(device_class, NULL, DEV_T, NULL, "gpio_device");
    if (IS_ERR(ptr_error)){
            class_destroy(device_class);
            unregister_chrdev_region(DEV_T, 1);
            printk(KERN_INFO "Device creation failed\n");
            return -EINVAL;
    }

    cdev_init(&c_dev, &fops);

    if (cdev_add(&c_dev, DEV_T, 1)){
            device_destroy(device_class, DEV_T);
            class_destroy(device_class);
            unregister_chrdev_region(DEV_T, 1);
            printk(KERN_INFO "Cdev add failed\n");
            return -EINVAL;
    }
    printk(KERN_INFO "Guten tag, GPIO driver initialized\n");
    return SUCCESS;

}


This runs with no errors, except no file “gpio_device” is created in /dev.

I’m cross compiling for ARM onto kernel 2.6.39.4. (using arm-linux-gcc)

As I understand it, device_create should be creating the /dev file.

Answer 1

I just figured out what was going on here.
We are using BuildRoot to create our custom
linux, and the it turns out we had compiled
out the udev device file management system.

So that’s why this doesn’t work.