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, 4 insertions, 7 deletions

diff --git a/src/dev/i8254xGBe.hh b/src/dev/i8254xGBe.hh
index 116fa5b95..3a3efb795 100644
--- a/src/dev/i8254xGBe.hh
+++ b/src/dev/i8254xGBe.hh
@@ -67,9 +67,6 @@ class IGbE : public EtherDevice
     uint8_t eeOpcode, eeAddr;
     uint16_t flash[iGbReg::EEPROM_SIZE];
 
-    // The drain event if we have one
-    DrainManager *drainManager;
-
     // packet fifos
     PacketFifo rxFifo;
     PacketFifo txFifo;
@@ -352,7 +349,7 @@ class IGbE : public EtherDevice
         virtual void updateHead(long h) { igbe->regs.rdh(h); }
         virtual void enableSm();
         virtual void fetchAfterWb() {
-            if (!igbe->rxTick && igbe->getDrainState() == DrainState::Running)
+            if (!igbe->rxTick && igbe->drainState() == DrainState::Running)
                 fetchDescriptors();
         }
 
@@ -414,7 +411,7 @@ class IGbE : public EtherDevice
         virtual void enableSm();
         virtual void actionAfterWb();
         virtual void fetchAfterWb() {
-            if (!igbe->txTick && igbe->getDrainState() == DrainState::Running)
+            if (!igbe->txTick && igbe->drainState() == DrainState::Running)
                 fetchDescriptors();
         }
         
@@ -541,8 +538,8 @@ class IGbE : public EtherDevice
     void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
     void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
 
-    unsigned int drain(DrainManager *dm);
-    void drainResume();
+    DrainState drain() M5_ATTR_OVERRIDE;
+    void drainResume() M5_ATTR_OVERRIDE;
 
 };