kernel: implement FreeInterrupt

This syscall is the opposite of ClaimInterrupt.

Signed-off-by: Sean Cross <sean@xobs.io>

kernel/src/irq.rs

@@ -81,6 +81,22 @@ pub fn interrupt_claim(
     }
 }
 
+pub fn interrupt_free(irq: usize, pid: PID) -> Result<(), xous_kernel::Error> {
+    // Unsafe is required since we're accessing a static mut array.
+    // However, we disable interrupts to prevent contention on this array.
+    unsafe {
+        if irq > IRQ_HANDLERS.len() {
+            Err(xous_kernel::Error::InterruptNotFound)
+        } else if !IRQ_HANDLERS[irq].map(|f| f.0 == pid).unwrap_or(false) {
+            Err(xous_kernel::Error::InterruptNotFound)
+        } else {
+            arch::irq::disable_irq(irq).unwrap();
+            IRQ_HANDLERS[irq] = None;
+            Ok(())
+        }
+    }
+}
+
 /// Iterate through the IRQ handlers and remove any handler that exists
 /// for the given PID.
 pub fn release_interrupts_for_pid(pid: PID) {

kernel/src/syscall.rs

@@ -3,7 +3,7 @@
 
 use crate::arch;
 use crate::arch::process::Process as ArchProcess;
-use crate::irq::interrupt_claim;
+use crate::irq::{interrupt_claim, interrupt_free};
 use crate::mem::{MemoryManager, PAGE_SIZE};
 use crate::server::{SenderID, WaitingMessage};
 use crate::services::SystemServices;
@@ -954,6 +954,9 @@ pub fn handle_inner(pid: PID, tid: TID, in_irq: bool, call: SysCall) -> SysCallR
             interrupt_claim(no, pid as definitions::PID, callback, arg)
                 .map(|_| xous_kernel::Result::Ok)
         }
+        SysCall::FreeInterrupt(no) => {
+            interrupt_free(no, pid as definitions::PID).map(|_| xous_kernel::Result::Ok)
+        }
         SysCall::Yield => do_yield(pid, tid),
         SysCall::ReturnToParent(_pid, _cpuid) => {
             unsafe {