diff --git a/kernel/src/arch/mipsel/mod.rs b/kernel/src/arch/mipsel/mod.rs
index 6347d3c..9bc4c4e 100644
--- a/kernel/src/arch/mipsel/mod.rs
+++ b/kernel/src/arch/mipsel/mod.rs
@@ -12,7 +12,6 @@ pub mod driver;
 
 use log::*;
 use mips::registers::cp0;
-use mips::instructions;
 
 #[cfg(feature = "board_malta")]
 #[path = "board/malta/mod.rs"]
@@ -40,7 +39,6 @@ pub extern fn rust_main() -> ! {
     let ebase = cp0::ebase::read_u32();
     let cpu_id = ebase & 0x3ff;
     let dtb_start = _dtb_start as usize;
-    let dtb_end = _dtb_end as usize;
 
     if cpu_id != BOOT_CPU_ID {
         // TODO: run others_main on other CPU
diff --git a/kernel/src/drivers/serial/16550_reg.rs b/kernel/src/drivers/serial/16550_reg.rs
index b624729..62330c4 100644
--- a/kernel/src/drivers/serial/16550_reg.rs
+++ b/kernel/src/drivers/serial/16550_reg.rs
@@ -1,5 +1,7 @@
 //! 16550 serial adapter driver for malta board
 
+#![allow(dead_code)]
+
 use core::fmt::{Write, Result, Arguments};
 use core::ptr::{read_volatile, write_volatile};
 use spin::Mutex;
diff --git a/kernel/src/sync/mutex.rs b/kernel/src/sync/mutex.rs
index e319fde..8af1460 100644
--- a/kernel/src/sync/mutex.rs
+++ b/kernel/src/sync/mutex.rs
@@ -216,7 +216,7 @@ impl MutexSupport for Spin {
         unsafe {
             #[cfg(target_arch = "x86_64")]
             asm!("pause" :::: "volatile");
-            #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+            #[cfg(any(target_arch = "riscv32", target_arch = "riscv64", target_arch = "mips"))]
             asm!("nop" :::: "volatile");
             #[cfg(target_arch = "aarch64")]
             asm!("yield" :::: "volatile");
@@ -254,7 +254,7 @@ impl MutexSupport for SpinNoIrq {
         unsafe {
             #[cfg(target_arch = "x86_64")]
             asm!("pause" :::: "volatile");
-            #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+            #[cfg(any(target_arch = "riscv32", target_arch = "riscv64", target_arch = "mips"))]
             asm!("nop" :::: "volatile");
             #[cfg(target_arch = "aarch64")]
             asm!("yield" :::: "volatile");
diff --git a/user b/user
index 67890ae..a460c5b 160000
--- a/user
+++ b/user
@@ -1 +1 @@
-Subproject commit 67890aeb4205083d5a95b1f70de92ae39b549c8c
+Subproject commit a460c5b32744292ed50922a159fa22c830aa61b9