dev-arm: drain implementation for SMMUv3

SMMUv3 is drained when (1) no SMMU translations are pending
on any of its slave interfaces and (2) no commands are stored
in the Command Queue waiting to be processed.

Change-Id: I81cef5fd821fa5e509e130af02aece5239493df5
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19309
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/dev/arm/smmu_v3.cc

@@ -741,7 +741,11 @@ SMMUv3::regStats()
 DrainState
 SMMUv3::drain()
 {
-    panic("SMMUv3 doesn't support draining\n");
+    // Wait until the Command Executor is not busy
+    if (commandExecutor.isBusy()) {
+        return DrainState::Draining;
+    }
+    return DrainState::Drained;
 }
 
 void

src/dev/arm/smmu_v3_cmdexec.cc

@@ -75,6 +75,8 @@ SMMUCommandExecProcess::main(Yield &yield)
         }
 
         busy = false;
+        // No more commands to process, signal the SMMU as drained
+        smmu.signalDrainDone();
 
         doSleep(yield);
     }

src/dev/arm/smmu_v3_slaveifc.cc

@@ -253,6 +253,16 @@ SMMUv3SlaveInterface::scheduleDeviceRetry()
     }
 }
 
+DrainState
+SMMUv3SlaveInterface::drain()
+{
+    // Wait until all SMMU translations are completed
+    if (xlateSlotsRemaining < params()->xlate_slots) {
+        return DrainState::Draining;
+    }
+    return DrainState::Drained;
+}
+
 SMMUv3SlaveInterface*
 SMMUv3SlaveInterfaceParams::create()
 {

src/dev/arm/smmu_v3_slaveifc.hh

@@ -56,6 +56,9 @@ class SMMUSlavePort;
 
 class SMMUv3SlaveInterface : public MemObject
 {
+  protected:
+    friend class SMMUTranslationProcess;
+
   public:
     SMMUv3 *smmu;
     SMMUTLB* microTLB;
@@ -124,6 +127,14 @@ class SMMUv3SlaveInterface : public MemObject
         delete mainTLB;
     }
 
+    const SMMUv3SlaveInterfaceParams *
+    params() const
+    {
+        return static_cast<const SMMUv3SlaveInterfaceParams *>(_params);
+    }
+
+    DrainState drain() override;
+
     void setSMMU(SMMUv3 *_smmu) { smmu = _smmu; }
     void sendRange();
 };

src/dev/arm/smmu_v3_transl.cc

@@ -94,6 +94,11 @@ SMMUTranslationProcess::~SMMUTranslationProcess()
 {
     // Increase number of pending translation slots on the slave interface
     ifc.xlateSlotsRemaining++;
+    // If no more SMMU translations are pending (all slots available),
+    // signal SMMU Slave Interface as drained
+    if (ifc.xlateSlotsRemaining == ifc.params()->xlate_slots) {
+        ifc.signalDrainDone();
+    }
 }
 
 void