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.

1 files changed, 8 insertions, 10 deletions

diff --git a/src/mem/xbar.cc b/src/mem/xbar.cc
index bc649581b..7316fbc21 100644
--- a/src/mem/xbar.cc
+++ b/src/mem/xbar.cc
@@ -145,7 +145,7 @@ BaseXBar::calcPacketTiming(PacketPtr pkt, Tick header_delay)
 template <typename SrcType, typename DstType>
 BaseXBar::Layer<SrcType,DstType>::Layer(DstType& _port, BaseXBar& _xbar,
                                        const std::string& _name) :
-    port(_port), xbar(_xbar), _name(_name), state(IDLE), drainManager(NULL),
+    port(_port), xbar(_xbar), _name(_name), state(IDLE),
     waitingForPeer(NULL), releaseEvent(this)
 {
 }
@@ -252,12 +252,10 @@ BaseXBar::Layer<SrcType,DstType>::releaseLayer()
         // waiting for the peer
         if (waitingForPeer == NULL)
             retryWaiting();
-    } else if (waitingForPeer == NULL && drainManager) {
+    } else if (waitingForPeer == NULL && drainState() == DrainState::Draining) {
         DPRINTF(Drain, "Crossbar done draining, signaling drain manager\n");
         //If we weren't able to drain before, do it now.
-        drainManager->signalDrainDone();
-        // Clear the drain event once we're done with it.
-        drainManager = NULL;
+        signalDrainDone();
     }
 }
 
@@ -587,18 +585,18 @@ BaseXBar::regStats()
 }
 
 template <typename SrcType, typename DstType>
-unsigned int
-BaseXBar::Layer<SrcType,DstType>::drain(DrainManager *dm)
+DrainState
+BaseXBar::Layer<SrcType,DstType>::drain()
 {
     //We should check that we're not "doing" anything, and that noone is
     //waiting. We might be idle but have someone waiting if the device we
     //contacted for a retry didn't actually retry.
     if (state != IDLE) {
         DPRINTF(Drain, "Crossbar not drained\n");
-        drainManager = dm;
-        return 1;
+        return DrainState::Draining;
+    } else {
+        return DrainState::Drained;
     }
-    return 0;
 }
 
 template <typename SrcType, typename DstType>