OSDev.org

NickJohnson wrote:I'm trying to write a (originally thought to be) simple function that will run through all of the functions of all of the slots of all of the buses in the PCI configuration space and locate all instances of a class and optionally a subclass, obviously for device detection purposes. Originally, I wrote it to scan through all three dimensions assuming they were contiguous, i.e. if bus 1 does not exist, bus 2 does not exist; same for slots and functions. Of course, I was completely wrong, which I realized after inspecting lspci on my laptop. I know that if function 0 does not exist for a slot, no other functions do, but are there any more rules like that that will save me from looping though (and doing at least two I/O cycles for) all 65536 possible combinations of bus, slot, and function fields? Is there any way to quickly figure out the topology of the buses or slots without actually checking each one?

void main(void) {
  scanDevices(0);
}

scanDevices(int bus) {
  for(device = 0; device < 32; device++) {
    if(vendorID(bus, device, 0) is valid) {
      checkDevice(bus, device, 0);
      if(headerType(bus, 0, 0) has_bit7_set) {
        for(function = 1; function < 8; function++) {
          if(vendorID(bus, device, function) is valid) checkDevice(bus, device, function);
          else break;
        }
      }
    }
  }
}

checkDevice(int bus, int device, int function) {
  if(headerType(bus, device, function) says_device_is_PCI_to_PCI_bridge) {
    printf("Found bridge: <details>\n");
    secondaryBus = get_secondary_bus((bus, device, function);
    scanDevices(secondaryBus);
  } else {
    printf("Found device: <details>\n");
  }
}

bewing wrote:As I understand it, all motherboards that support PCI are supposed to support BIOS function INT1A AX=B101 -- IIRC CL is the maximum PCI bus number configured on the machine, so you can discount all of them above that.

bewing wrote:Note however that bochs & qemu do not support this BIOS function. At least the last time I tested it.

NickJohnson wrote:@Brendan: so, you're saying I should recursively run through each bus by following the PCI-PCI bridges? That seems like a good idea, provided I interpreted it right of course.