PCIe Driver - How does user space access it?

Question

I am writing a PCIe driver for Linux, currently without DMA, and need to know how to read and write to the PCIe device once it is enabled from user space.

In the driver I do the basics in probe():

pci_enable_device();
pci_request_regions();
pci_iomap();

But then how do I access this memory from user space to read and write? Do I add file operations to my PCIe driver? Does the memory from pci_iomap show up some place where the user space code can call:

open('mapped memory location');
mmap(...);

If so then what is the location?

Note: the PCIe device will not plugging into any Linux subsystems such as audio, Ethernet, etc.

Answer 1

You can register devices using functions like register_chrdev and device_create. Consider the kernel source for /dev/null and /dev/mem:

static int __init chr_dev_init(void)
{
    int minor;

    if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
        printk("unable to get major %d for memory devs\n", MEM_MAJOR);

    mem_class = class_create(THIS_MODULE, "mem");
    if (IS_ERR(mem_class))
        return PTR_ERR(mem_class);

    mem_class->devnode = mem_devnode;
    for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
        if (!devlist[minor].name)
            continue;

        /*
         * Create /dev/port?
         */
        if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
            continue;

        device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
                  NULL, devlist[minor].name);
    }

    return tty_init();
}

fs_initcall(chr_dev_init);