Kernel/aarch64: Add basic support for PSCI and HVC calls

This makes it possible to shut down and reboot the QEMU virt machine.

Kernel/Arch/aarch64/PSCI.cpp

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2025, the SerenityOS developers
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/aarch64/PSCI.h>
+#include <Kernel/Firmware/DeviceTree/DeviceTree.h>
+
+// https://developer.arm.com/documentation/den0022/latest/
+namespace Kernel::PSCI {
+
+enum class Function : u32 {
+    SystemOff = 0x8400'0008,
+    SystemReset = 0x8400'0009,
+};
+
+static FlatPtr call(Function function, FlatPtr arg0, FlatPtr arg1, FlatPtr arg2)
+{
+    // 5.2.1 Register usage in arguments and return values
+    // "For [PSCI] versions using 64-bit parameters, the arguments are passed in X0 to X3, with return values in X0."
+    register FlatPtr x0 asm("x0") = static_cast<FlatPtr>(function);
+    register FlatPtr x1 asm("x1") = arg0;
+    register FlatPtr x2 asm("x2") = arg1;
+    register FlatPtr x3 asm("x3") = arg2;
+
+    // NOTE: x4-x17 are marked as clobbered since SMCCC 1.0 doesn't
+    // require them to be preserved across SMC or HVC calls.
+    asm volatile(
+        "hvc #0"
+        : "+r"(x0), "+r"(x1), "+r"(x2), "+r"(x3)
+        :
+        : "memory", "x4", "x5", "x6", "x7", "x8", "x9", "x10", "x11", "x12", "x13", "x14", "x15", "x16", "x17");
+
+    return x0;
+}
+
+bool is_supported()
+{
+    // https://www.kernel.org/doc/Documentation/devicetree/bindings/arm/psci.txt
+    // FIXME: Make this a DeviceTree::Driver, and don't assume that the psci node is a child of the root node.
+    auto psci = DeviceTree::get().get_child("psci"sv);
+    if (!psci.has_value())
+        return false;
+
+    // NOTE: We reject "arm,psci" on purpose, since these old devices don't have standardized function IDs.
+    if (!psci->is_compatible_with("arm,psci-0.2"sv) && !psci->is_compatible_with("arm,psci-1.0"sv))
+        return false;
+
+    auto method = psci->get_property("method"sv);
+    if (!method.has_value()) {
+        dbgln("PSCI: No method property found");
+        return false;
+    }
+
+    // Currently, we only support HVC (as opposed to SMC). While SMC is very similar to HVC, only the latter has been tested so far.
+    if (method->as_string() != "hvc"sv)
+        return false;
+
+    return true;
+}
+
+void poweroff()
+{
+    call(Function::SystemOff, 0, 0, 0);
+}
+
+void reset()
+{
+    call(Function::SystemReset, 0, 0, 0);
+}
+
+}

Kernel/Arch/aarch64/PSCI.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2025, the SerenityOS developers
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Kernel::PSCI {
+
+bool is_supported();
+void poweroff();
+void reset();
+
+}

Kernel/Arch/aarch64/PowerState.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <Kernel/Arch/PowerState.h>
+#include <Kernel/Arch/aarch64/PSCI.h>
 #include <Kernel/Arch/aarch64/RPi/Watchdog.h>
 #include <Kernel/Firmware/DeviceTree/DeviceTree.h>
 
@@ -12,10 +13,15 @@ namespace Kernel {
 
 void arch_specific_reboot()
 {
+    if (PSCI::is_supported())
+        PSCI::reset();
 }
 
 void arch_specific_poweroff()
 {
+    if (PSCI::is_supported())
+        PSCI::poweroff();
+
     if (DeviceTree::get().is_compatible_with("raspberrypi,3-model-b"sv) || DeviceTree::get().is_compatible_with("raspberrypi,4-model-b"sv))
         RPi::Watchdog::the().system_shutdown();
 }

Kernel/CMakeLists.txt

@@ -508,6 +508,7 @@ elseif("${SERENITY_ARCH}" STREQUAL "aarch64")
         Arch/aarch64/Interrupts.cpp
         Arch/aarch64/Interrupts/GIC.cpp
         Arch/aarch64/MainIdRegister.cpp
+        Arch/aarch64/PSCI.cpp
         Arch/aarch64/PageDirectory.cpp
         Arch/aarch64/Processor.cpp
         Arch/aarch64/PowerState.cpp