OpenSBI: Added timer extension

NOTE: I didn't switch to the new functions in the kernel because for
some reason we get a page fault when trying to fetch the first
instruction of set_timer(addi sp, sp, -48). I doubt this is related to
the set_timer funcion itself and is instead some kind of paging or
linking problem because it works fine with paging disabled and really
just doesnt make sense.

kernel/drivers/opensbi/extensions/timer.cpp

@@ -0,0 +1,25 @@
+#include "opensbi/extensions/timer.h"
+
+namespace drivers {
+namespace opensbi::timer {
+
+    namespace {
+        enum class ExtensionId {
+            TIMER = 0x54494D45
+        };
+
+        enum class FunctionId {
+            SET_TIMER,
+        };
+    }
+
+    SbiRet set_timer(uint64_t stime_value) {
+        return ecall(
+            static_cast<sbiword_t>(ExtensionId::TIMER),
+            static_cast<sbiword_t>(FunctionId::SET_TIMER),
+            stime_value);
+    }
+
+}  // End namespace opensbi::timer
+}  // End namespace drivers
+

kernel/drivers/opensbi/include/opensbi/extensions/timer.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "opensbi/opensbi.h"
+
+namespace drivers {
+namespace opensbi::timer {
+
+    SbiRet set_timer(uint64_t stime_value);
+
+}  // End namespace opensbi::timer
+}  // End namespace drivers

kernel/drivers/opensbi/meson.build

@@ -1,7 +1,9 @@
 kernel_sources += [
     files(
         'opensbi.cpp',
-        'extensions/legacy.cpp'
+        'extensions/legacy.cpp',
+        'extensions/base.cpp',
+        'extensions/timer.cpp'
     ),
 ]