PCIe Driver - How Does User Space Access It?

Question

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

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

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

But how can I access this memory from user space for reading and writing? Do I add files to my PCIe driver? Does the pci_iomap memory appear in any place where user space code can be called:

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

If so, what is the location?

Note. A PCIe device will not connect to any Linux subsystem, such as audio, Ethernet, etc.

Answer 1

You can register devices using functions such as register_chrdev and device_create . Consider the source 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); 

Answer 2

If you just want to export memory from kernel space to user space and get interrupts, consider a UIO driver .

With its help, all calls will be performed through the / dev / uioX file. You can do mmap () on it to export memory, and you can read (with read lock) to “catch” the interrupt.

UIO is great for PCIe, there is already a driver in the kernel for it.