Add the qemu exit method for LoongArch in OSTD

ostd/src/arch/loongarch/qemu.rs

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: MPL-2.0
+
+//! Providing the ability to exit QEMU and return a value as debug result.
+
+use crate::arch::{boot::DEVICE_TREE, mm::paddr_to_daddr};
+
+/// The exit code of QEMU.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum QemuExitCode {
+    /// The code that indicates a successful exit.
+    Success,
+    /// The code that indicates a failed exit.
+    Failed,
+}
+
+/// Exits QEMU with the given exit code.
+//  FIXME: Support the transfer of the exit code to QEMU and multiple platforms.
+pub fn exit_qemu(_exit_code: QemuExitCode) -> ! {
+    let (poweroff_addr, poweroff_value) = lookup_poweroff_paddr_value().unwrap();
+    let poweroff_daddr = paddr_to_daddr(poweroff_addr) as *mut u8;
+
+    // SAFETY: It is safe because the poweroff address is acquired from the device tree,
+    // and be mapped in DMW2.
+    unsafe {
+        core::ptr::write_volatile(poweroff_daddr, poweroff_value);
+    }
+    unreachable!("Qemu does not exit");
+}
+
+// FIXME: We should reserve the address region in `io_mem_allocator`.
+fn lookup_poweroff_paddr_value() -> Option<(usize, u8)> {
+    let device_tree = DEVICE_TREE.get().unwrap();
+
+    let ged = device_tree.find_node("/ged")?;
+    if !ged.compatible()?.all().any(|c| c == "syscon") {
+        return None;
+    }
+    let ged_reg_base_address = ged.reg()?.next()?.starting_address as usize;
+
+    let poweroff = device_tree.find_node("/poweroff").unwrap();
+    if !poweroff.compatible()?.all().any(|c| c == "syscon-poweroff") {
+        return None;
+    }
+    let poweroff_offset = poweroff.property("offset")?.as_usize()?;
+    let poweroff_value = poweroff.property("value")?.as_usize()? as u8;
+
+    Some((ged_reg_base_address + poweroff_offset, poweroff_value))
+}