diff --git a/drivers/acpid/src/main.rs b/drivers/acpid/src/main.rs
index d1c7b518a8..6aa29ccf97 100644
--- a/drivers/acpid/src/main.rs
+++ b/drivers/acpid/src/main.rs
@@ -166,9 +166,14 @@ fn daemon(daemon: daemon::Daemon) -> ! {
                     acpi_context.exit_s2idle();
                 }
                 3 => {
-                    // s3 wake (Phase II)
-                    log::info!("s3 wake (Phase II — not yet implemented)");
-                    // TODO: Phase II
+                    // s3 wake (Phase II.X.W)
+                    // Run the standard S3 resume AML sequence:
+                    // \_SST(2) -> \_WAK(3) -> \_SST(1). The kernel
+                    // trampoline at s3_resume::s3_trampoline
+                    // has already restored the kernel state. The
+                    // acpid's job is the AML wake sequence.
+                    log::info!("s3 wake: running \\_SST(2) -> \\_WAK(3) -> \\_SST(1)");
+                    acpi_context.wake_from_sleep_state(3);
                 }
                 other => {
                     log::warn!("unknown kstop reason {}, treating as shutdown", other);
diff --git a/drivers/acpid/src/scheme.rs b/drivers/acpid/src/scheme.rs
index da9180948a..5407e38395 100644
--- a/drivers/acpid/src/scheme.rs
+++ b/drivers/acpid/src/scheme.rs
@@ -195,6 +195,25 @@ impl<'acpi, 'sock> AcpiScheme<'acpi, 'sock> {
         handle.call_wo(&[], CallFlags::empty(), &[verb])?;
         Ok(())
     }
+
+    /// Phase II.X.W: write the kernel's S3 resume
+    /// trampoline address to FACS.xfirmware_waking_vector so
+    /// the platform firmware jumps to it on S3 wake.
+    ///
+    /// `trampoline_addr` is the address of the kernel's
+    /// `s3_resume::s3_trampoline` function. The kernel
+    /// writes this to FACS via the `SetS3WakingVector`
+    /// AcPiVerb (verb 5).
+    pub fn kstop_enter_s3(&self, trampoline_addr: u64) -> syscall::Result<()> {
+        let handle = self.kstop_fd.ok_or(syscall::error::Error::new(syscall::error::EBADF))?;
+        let verb = AcpiVerb::SetS3WakingVector as u64;
+        // Payload: 8-byte little-endian u64 (the trampoline
+        // address). The kernel's `SetS3WakingVector` handler
+        // requires the payload to be exactly 8 bytes.
+        let payload = trampoline_addr.to_ne_bytes();
+        handle.call_wo(&payload, CallFlags::empty(), &[verb])?;
+        Ok(())
+    }
 }
 
 fn parse_hex_digit(hex: u8) -> Option<u8> {