size_t UHCIController::poll_transfer_queue(QueueHead& transfer_queue)
{
    Transfer* transfer = transfer_queue.transfer();
    TransferDescriptor* descriptor = transfer_queue.get_first_td();
    bool transfer_still_in_progress = false;
    size_t transfer_size = 0;

    while (descriptor) {
        u32 status = descriptor->status();

        if (status & TransferDescriptor::StatusBits::Active) {
            transfer_still_in_progress = true;
            break;
        }

        if (status & TransferDescriptor::StatusBits::ErrorMask) {
            transfer->set_complete();
            transfer->set_error_occurred();
            dbgln_if(UHCI_DEBUG, "UHCIController: Transfer failed! Reason: {:08x}", status);
            return 0;
        }

        transfer_size += descriptor->actual_packet_length();
        descriptor = descriptor->next_td();
    }

    if (!transfer_still_in_progress)
        transfer->set_complete();

    return transfer_size;
}