sim: Refactor and simplify the drain API

The drain() call currently passes around a DrainManager pointer, which
is now completely pointless since there is only ever one global
DrainManager in the system. It also contains vestiges from the time
when SimObjects had to keep track of their child objects that needed
draining.

This changeset moves all of the DrainState handling to the Drainable
base class and changes the drain() and drainResume() calls to reflect
this. Particularly, the drain() call has been updated to take no
parameters (the DrainManager argument isn't needed) and return a
DrainState instead of an unsigned integer (there is no point returning
anything other than 0 or 1 any more). Drainable objects should return
either DrainState::Draining (equivalent to returning 1 in the old
system) if they need more time to drain or DrainState::Drained
(equivalent to returning 0 in the old system) if they are already in a
consistent state. Returning DrainState::Running is considered an
error.

Drain done signalling is now done through the signalDrainDone() method
in the Drainable class instead of using the DrainManager directly. The
new call checks if the state of the object is DrainState::Draining
before notifying the drain manager. This means that it is safe to call
signalDrainDone() without first checking if the simulator has
requested draining. The intention here is to reduce the code needed to
implement draining in simple objects.

3 files changed, 12 insertions, 23 deletions

diff --git a/src/arch/arm/table_walker.cc b/src/arch/arm/table_walker.cc
index 297054131..3e61a4bd6 100644
--- a/src/arch/arm/table_walker.cc
+++ b/src/arch/arm/table_walker.cc
@@ -57,7 +57,7 @@
 using namespace ArmISA;
 
 TableWalker::TableWalker(const Params *p)
-    : MemObject(p), drainManager(NULL),
+    : MemObject(p),
       stage2Mmu(NULL), port(NULL), masterId(Request::invldMasterId),
       isStage2(p->is_stage2), tlb(NULL),
       currState(NULL), pending(false),
@@ -137,17 +137,17 @@ TableWalker::WalkerState::WalkerState() :
 void
 TableWalker::completeDrain()
 {
-    if (drainManager && stateQueues[L1].empty() && stateQueues[L2].empty() &&
+    if (drainState() == DrainState::Draining &&
+        stateQueues[L1].empty() && stateQueues[L2].empty() &&
         pendingQueue.empty()) {
-        setDrainState(DrainState::Drained);
+
         DPRINTF(Drain, "TableWalker done draining, processing drain event\n");
-        drainManager->signalDrainDone();
-        drainManager = NULL;
+        signalDrainDone();
     }
 }
 
-unsigned int
-TableWalker::drain(DrainManager *dm)
+DrainState
+TableWalker::drain()
 {
     bool state_queues_not_empty = false;
 
@@ -159,25 +159,17 @@ TableWalker::drain(DrainManager *dm)
     }
 
     if (state_queues_not_empty || pendingQueue.size()) {
-        drainManager = dm;
-        setDrainState(DrainState::Draining);
         DPRINTF(Drain, "TableWalker not drained\n");
-
-        // return port drain count plus the table walker itself needs to drain
-        return 1;
+        return DrainState::Draining;
     } else {
-        setDrainState(DrainState::Drained);
         DPRINTF(Drain, "TableWalker free, no need to drain\n");
-
-        // table walker is drained, but its ports may still need to be drained
-        return 0;
+        return DrainState::Drained;
     }
 }
 
 void
 TableWalker::drainResume()
 {
-    Drainable::drainResume();
     if (params()->sys->isTimingMode() && currState) {
         delete currState;
         currState = NULL;
diff --git a/src/arch/arm/table_walker.hh b/src/arch/arm/table_walker.hh
index a5327cd95..e973e9a74 100644
--- a/src/arch/arm/table_walker.hh
+++ b/src/arch/arm/table_walker.hh
@@ -819,9 +819,6 @@ class TableWalker : public MemObject
      * currently busy. */
     std::list<WalkerState *> pendingQueue;
 
-    /** If we're draining keep the drain event around until we're drained */
-    DrainManager *drainManager;
-
     /** The MMU to forward second stage look upts to */
     Stage2MMU *stage2Mmu;
 
@@ -894,8 +891,8 @@ class TableWalker : public MemObject
     bool haveLargeAsid64() const { return _haveLargeAsid64; }
     /** Checks if all state is cleared and if so, completes drain */
     void completeDrain();
-    unsigned int drain(DrainManager *dm);
-    virtual void drainResume();
+    DrainState drain() M5_ATTR_OVERRIDE;
+    virtual void drainResume() M5_ATTR_OVERRIDE;
 
     virtual BaseMasterPort& getMasterPort(const std::string &if_name,
                                           PortID idx = InvalidPortID);
diff --git a/src/arch/arm/tlb.hh b/src/arch/arm/tlb.hh
index 28b99a8e0..63707dba2 100644
--- a/src/arch/arm/tlb.hh
+++ b/src/arch/arm/tlb.hh
@@ -284,7 +284,7 @@ class TLB : public BaseTLB
             bool callFromS2);
     Fault finalizePhysical(RequestPtr req, ThreadContext *tc, Mode mode) const;
 
-    void drainResume();
+    void drainResume() M5_ATTR_OVERRIDE;
 
     // Checkpointing
     void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;