pwr: Low-power idle power state for idle CPUs

Add functionality to the BaseCPU that will put the entire CPU
into a low-power idle state whenever all threads in it are idle.

Change-Id: I984d1656eb0a4863c87ceacd773d2d10de5cfd2b

1 files changed, 28 insertions, 1 deletions

diff --git a/src/cpu/base.cc b/src/cpu/base.cc
index fbd8af99a..aaf5a7a93 100644
--- a/src/cpu/base.cc
+++ b/src/cpu/base.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2012 ARM Limited
+ * Copyright (c) 2011-2012,2016 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -64,6 +64,7 @@
 #include "debug/SyscallVerbose.hh"
 #include "mem/page_table.hh"
 #include "params/BaseCPU.hh"
+#include "sim/clocked_object.hh"
 #include "sim/full_system.hh"
 #include "sim/process.hh"
 #include "sim/sim_events.hh"
@@ -355,6 +356,11 @@ BaseCPU::startup()
     if (params()->progress_interval) {
         new CPUProgressEvent(this, params()->progress_interval);
     }
+
+    // Assumption CPU start to operate instantaneously without any latency
+    if (ClockedObject::pwrState() == Enums::PwrState::UNDEFINED)
+        ClockedObject::pwrState(Enums::PwrState::ON);
+
 }
 
 ProbePoints::PMUUPtr
@@ -475,6 +481,27 @@ BaseCPU::findContext(ThreadContext *tc)
 }
 
 void
+BaseCPU::activateContext(ThreadID thread_num)
+{
+    // For any active thread running, update CPU power state to active (ON)
+    ClockedObject::pwrState(Enums::PwrState::ON);
+}
+
+void
+BaseCPU::suspendContext(ThreadID thread_num)
+{
+    // Check if all threads are suspended
+    for (auto t : threadContexts) {
+        if (t->status() != ThreadContext::Suspended) {
+            return;
+        }
+    }
+
+    // All CPU threads suspended, enter lower power state for the CPU
+    ClockedObject::pwrState(Enums::PwrState::CLK_GATED);
+}
+
+void
 BaseCPU::switchOut()
 {
     assert(!_switchedOut);