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.

4 files changed, 15 insertions, 48 deletions

diff --git a/src/dev/arm/flash_device.cc b/src/dev/arm/flash_device.cc
index e4bfcf5c9..b651a1eeb 100644
--- a/src/dev/arm/flash_device.cc
+++ b/src/dev/arm/flash_device.cc
@@ -86,7 +86,6 @@ FlashDevice::FlashDevice(const FlashDeviceParams* p):
     pagesPerDisk(0),
     blocksPerDisk(0),
     planeMask(numPlanes - 1),
-    drainManager(NULL),
     planeEventQueue(numPlanes),
     planeEvent(this)
 {
@@ -587,26 +586,16 @@ FlashDevice::unserialize(CheckpointIn &cp)
  * Drain; needed to enable checkpoints
  */
 
-unsigned int
-FlashDevice::drain(DrainManager *dm)
+DrainState
+FlashDevice::drain()
 {
-    unsigned int count = 0;
-
     if (planeEvent.scheduled()) {
-        count = 1;
-        drainManager = dm;
-    } else {
-        DPRINTF(Drain, "Flash device in drained state\n");
-    }
-
-    if (count) {
         DPRINTF(Drain, "Flash device is draining...\n");
-        setDrainState(DrainState::Draining);
+        return DrainState::Draining;
     } else {
-        DPRINTF(Drain, "Flash device drained\n");
-        setDrainState(DrainState::Drained);
+        DPRINTF(Drain, "Flash device in drained state\n");
+        return DrainState::Drained;
     }
-    return count;
 }
 
 /**
@@ -616,15 +605,13 @@ FlashDevice::drain(DrainManager *dm)
 void
 FlashDevice::checkDrain()
 {
-    if (drainManager == NULL) {
+    if (drainState() == DrainState::Draining)
         return;
-    }
 
     if (planeEvent.when() > curTick()) {
         DPRINTF(Drain, "Flash device is still draining\n");
     } else {
         DPRINTF(Drain, "Flash device is done draining\n");
-        drainManager->signalDrainDone();
-        drainManager = NULL;
+        signalDrainDone();
     }
 }
diff --git a/src/dev/arm/flash_device.hh b/src/dev/arm/flash_device.hh
index 330299451..891217cbf 100644
--- a/src/dev/arm/flash_device.hh
+++ b/src/dev/arm/flash_device.hh
@@ -62,7 +62,7 @@ class FlashDevice : public AbstractNVM
     ~FlashDevice();
 
     /** Checkpoint functions*/
-    unsigned int drain(DrainManager *dm);
+    DrainState drain() M5_ATTR_OVERRIDE;
     void checkDrain();
 
     void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
@@ -176,13 +176,6 @@ class FlashDevice : public AbstractNVM
     uint32_t planeMask;
 
     /**
-     * drain manager
-     * Needed to be able to implement checkpoint functionality
-     */
-
-    DrainManager *drainManager;
-
-    /**
      * when the disk is first started we are unsure of the number of
      * used pages, this variable will help determining what we do know.
      */
diff --git a/src/dev/arm/ufs_device.cc b/src/dev/arm/ufs_device.cc
index 696aeba6f..61b125ef5 100644
--- a/src/dev/arm/ufs_device.cc
+++ b/src/dev/arm/ufs_device.cc
@@ -733,7 +733,6 @@ UFSHostDevice::UFSHostDevice(const UFSHostDeviceParams* p) :
     transferTrack(0),
     taskCommandTrack(0),
     idlePhaseStart(0),
-    drainManager(NULL),
     SCSIResumeEvent(this),
     UTPEvent(this)
 {
@@ -2316,18 +2315,15 @@ UFSHostDevice::unserialize(CheckpointIn &cp)
  * Drain; needed to enable checkpoints
  */
 
-unsigned int
-UFSHostDevice::drain(DrainManager *dm)
+DrainState
+UFSHostDevice::drain()
 {
     if (UFSHCIMem.TRUTRLDBR) {
-        drainManager = dm;
         DPRINTF(UFSHostDevice, "UFSDevice is draining...\n");
-        setDrainState(DrainState::Draining);
-        return 1;
+        return DrainState::Draining;
     } else {
         DPRINTF(UFSHostDevice, "UFSDevice drained\n");
-        setDrainState(DrainState::Drained);
-        return 0;
+        return DrainState::Drained;
     }
 }
 
@@ -2338,16 +2334,14 @@ UFSHostDevice::drain(DrainManager *dm)
 void
 UFSHostDevice::checkDrain()
 {
-    if (drainManager == NULL) {
+    if (drainState() != DrainState::Draining)
         return;
-    }
 
     if (UFSHCIMem.TRUTRLDBR) {
         DPRINTF(UFSHostDevice, "UFSDevice is still draining; with %d active"
             " doorbells\n", activeDoorbells);
     } else {
         DPRINTF(UFSHostDevice, "UFSDevice is done draining\n");
-        drainManager->signalDrainDone();
-        drainManager = NULL;
+        signalDrainDone();
     }
 }
diff --git a/src/dev/arm/ufs_device.hh b/src/dev/arm/ufs_device.hh
index 15e983ad8..716b1bdcb 100644
--- a/src/dev/arm/ufs_device.hh
+++ b/src/dev/arm/ufs_device.hh
@@ -173,7 +173,7 @@ class UFSHostDevice : public DmaDevice
 
     UFSHostDevice(const UFSHostDeviceParams* p);
 
-    unsigned int drain(DrainManager *dm);
+    DrainState drain() M5_ATTR_OVERRIDE;
     void checkDrain();
     void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
     void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;
@@ -1053,13 +1053,6 @@ class UFSHostDevice : public DmaDevice
     Tick idlePhaseStart;
 
     /**
-     * drain manager
-     * Needed to be able to implement checkpoint functionality
-     */
-
-    DrainManager *drainManager;
-
-    /**
      * logic units connected to the UFS Host device
      * Note again that the "device" as such is represented by one or multiple
      * logic units.