You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/rCore/kernel/src/drivers/irq
    
    the code of the file until where you have to start completion: use super::Driver;
use crate::arch::interrupt::enable_irq;
use alloc::collections::btree_map::Entry;
use alloc::collections::BTreeMap;
use alloc::sync::Arc;
use alloc::vec::Vec;

#[cfg(feature = "board_raspi3")]
pub mod bcm2837;
pub mod plic;

// Irq manager
pub struct IrqManager {
    // is root manager?
    root: bool,
    // drivers that only respond to specific irq
    mapping: BTreeMap<usize, Vec<Arc<dyn Driver>>>,
    // drivers
    
    pub fn register_irq(&mut self, irq: usize, driver: Arc<dyn Driver>) {
        // for root manager, enable irq in arch
        // for other interrupt controllers, enable irq before calling this function
        if self.root {
            enable_irq(irq);
        }
        match self.mapping.entry(irq) {
            Entry::Occupied(mut e) => {
                e.get_mut().push(driver);
            }
            Entry::Vacant(e) => {
                let mut v = Vec::new();
                v.push(driver);
                e.insert(v);
            }
        }
    }