arch-arm: Add an option to use 64-bit PMU counters

Add support for 64-bit PMU counter registers (PMEVCNTR<n>_EL0), as
specified in Armv8-A.

The counter registers are 32-bit by default, but 64-bit counters can
be chosen using the `ArmPMU.use64bitCounters` parameter.

Change-Id: Idb838a7438c7711438a7e078278bed21710049af
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69683
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/arch/arm/ArmPMU.py

@@ -1,5 +1,5 @@
 # -*- mode:python -*-
-# Copyright (c) 2009-2014, 2017, 2020 ARM Limited
+# Copyright (c) 2009-2014, 2017, 2020, 2022 Arm Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -215,3 +215,11 @@ class ArmPMU(SimObject):
     platform = Param.Platform(Parent.any, "Platform this device is part of.")
     eventCounters = Param.Int(31, "Number of supported PMU counters")
     interrupt = Param.ArmInterruptPin("PMU interrupt")
+
+    # 64-bit PMU event counters are officially supported when
+    # Armv8.5-A FEAT_PMUv3p5 is implemented. This parameter is not a
+    # full implementation of FEAT_PMUv3p5.
+    use64bitCounters = Param.Bool(
+        False,
+        "Choose whether to use 64-bit or " "32-bit PMEVCNTR<n>_EL0 registers.",
+    )

src/arch/arm/pmu.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2014, 2017-2019 ARM Limited
+ * Copyright (c) 2011-2014, 2017-2019, 2022 Arm Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -56,12 +56,13 @@ const RegVal PMU::reg_pmcr_wr_mask = 0x39;
 
 PMU::PMU(const ArmPMUParams &p)
     : SimObject(p), BaseISADevice(),
+      use64bitCounters(p.use64bitCounters),
       reg_pmcnten(0), reg_pmcr(0),
       reg_pmselr(0), reg_pminten(0), reg_pmovsr(0),
       reg_pmceid0(0),reg_pmceid1(0),
       clock_remainder(0),
       maximumCounterCount(p.eventCounters),
-      cycleCounter(*this, maximumCounterCount),
+      cycleCounter(*this, maximumCounterCount, p.use64bitCounters),
       cycleCounterEventId(p.cycleEventId),
       swIncrementEvent(nullptr),
       reg_pmcr_conf(0),
@@ -175,7 +176,7 @@ PMU::regProbeListeners()
     // at this stage all probe configurations are done
     // counters can be configured
     for (uint32_t index = 0; index < maximumCounterCount-1; index++) {
-        counters.emplace_back(*this, index);
+        counters.emplace_back(*this, index, use64bitCounters);
     }
 
     std::shared_ptr<PMUEvent> event = getEvent(cycleCounterEventId);
@@ -685,6 +686,7 @@ PMU::serialize(CheckpointOut &cp) const
 {
     DPRINTF(Checkpoint, "Serializing Arm PMU\n");
 
+    SERIALIZE_SCALAR(use64bitCounters);
     SERIALIZE_SCALAR(reg_pmcr);
     SERIALIZE_SCALAR(reg_pmcnten);
     SERIALIZE_SCALAR(reg_pmselr);
@@ -705,6 +707,7 @@ PMU::unserialize(CheckpointIn &cp)
 {
     DPRINTF(Checkpoint, "Unserializing Arm PMU\n");
 
+    UNSERIALIZE_SCALAR(use64bitCounters);
     UNSERIALIZE_SCALAR(reg_pmcr);
     UNSERIALIZE_SCALAR(reg_pmcnten);
     UNSERIALIZE_SCALAR(reg_pmselr);

src/arch/arm/pmu.hh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2014, 2017-2018 ARM Limited
+ * Copyright (c) 2011-2014, 2017-2018, 2022 Arm Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -413,9 +413,10 @@ class PMU : public SimObject, public ArmISA::BaseISADevice
     /** State of a counter within the PMU. **/
     struct CounterState : public Serializable
     {
-        CounterState(PMU &pmuReference, uint64_t counter_id)
+        CounterState(PMU &pmuReference, uint64_t counter_id,
+                     const bool is_64_bit)
             : eventId(0), filter(0), enabled(false),
-              overflow64(false), sourceEvent(nullptr),
+              overflow64(is_64_bit), sourceEvent(nullptr),
               counterId(counter_id), value(0), resetValue(false),
               pmu(pmuReference) {}
 
@@ -572,6 +573,9 @@ class PMU : public SimObject, public ArmISA::BaseISADevice
     void updateAllCounters();
 
   protected: /* State that needs to be serialized */
+    /** Determine whether to use 64-bit or 32-bit counters. */
+    bool use64bitCounters;
+
     /** Performance Monitor Count Enable Register */
     RegVal reg_pmcnten;