The final goal is to be able to write to a PCIE device from the kernel, without the already made functions, to understand the inner working (and then, obviously, use them again).
I saw the PCIE specs which are 800+ pages (the 3.0 especially).
Huge is not enough to describe that.
I cannot afford to go along those at the step I currently am (reading 2.0 and 3.1 would be very time consuming).
I read many sources and it seems that we can write to pcie via messages (and not buses anymore like in pci). Pcie should be memory mapped so I think that we could write to that memory from the kernel and aknowledge the driver that we did it.
The driver will then make the out(l/b) assembly instruction to notify the device in question.
This my very high level understanding of pcie (I don't want to dive into the spec details now). It may not be correct though.
If someone could tell me where I am wrong in my thinking, that would be very helpful.
Here is the pseudo code of my thinking (no error checking and such):
static int64_t my_driver_address;
pcie_write_device(uint32_t * my_data_physical_address) {
// we pass the physical address where the data is. It has to be contiguous.
pcie_send_address(&my_driver_address, my_data_physical_address);
// now the device is acknowledged that some data has been mmaped, knows where and will treat it as such
}
pcie_read_device(anytype_t ** buff){
// this function calls the inq assembly instruction and store the resulting address in the pointer
ptr * address_to_read = pcie_get_data();
// read the mmaped memory region. No mem allocation code.
*buf = get_data_from region(address_to_read);
// now data from device is in the buff, ready to be sent to the OS or anything..
}
