mem-cache: Add getter and setter to CacheBlk::whenReady

Add a getter and a setter function to access CacheBlk::whenReady
to encapsulate the variable and allow error checking. This error
checking consists on verifying that writes to a block after it
has been inserted follow a chronological order.

As a side effect, tickInserted retain its value until updated,
that is, it is not reset in invalidate().

Change-Id: Idc3c5a99c3f002ee9acc2424f00e554877fd3a69
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/14715
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/base.cc

@@ -900,10 +900,11 @@ BaseCache::calculateAccessLatency(const CacheBlk* blk,
         }
 
         // Check if the block to be accessed is available. If not, apply the
-        // access latency on top of block->whenReady.
-        if (blk->whenReady > curTick() &&
-            ticksToCycles(blk->whenReady - curTick()) > lat) {
-            lat += ticksToCycles(blk->whenReady - curTick());
+        // access latency on top of when the block is ready to be accessed.
+        const Tick when_ready = blk->getWhenReady();
+        if (when_ready > curTick() &&
+            ticksToCycles(when_ready - curTick()) > lat) {
+            lat += ticksToCycles(when_ready - curTick());
         }
     }
 
@@ -1024,8 +1025,8 @@ BaseCache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
         DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
         incHitCount(pkt);
         // populate the time when the block will be ready to access.
-        blk->whenReady = clockEdge(fillLatency) + pkt->headerDelay +
-            pkt->payloadDelay;
+        blk->setWhenReady(clockEdge(fillLatency) + pkt->headerDelay +
+            pkt->payloadDelay);
         return true;
     } else if (pkt->cmd == MemCmd::CleanEvict) {
         if (blk) {
@@ -1081,8 +1082,8 @@ BaseCache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
 
         incHitCount(pkt);
         // populate the time when the block will be ready to access.
-        blk->whenReady = clockEdge(fillLatency) + pkt->headerDelay +
-            pkt->payloadDelay;
+        blk->setWhenReady(clockEdge(fillLatency) + pkt->headerDelay +
+            pkt->payloadDelay);
         // if this a write-through packet it will be sent to cache
         // below
         return !pkt->writeThrough();
@@ -1212,8 +1213,7 @@ BaseCache::handleFill(PacketPtr pkt, CacheBlk *blk, PacketList &writebacks,
         pkt->writeDataToBlock(blk->data, blkSize);
     }
     // We pay for fillLatency here.
-    blk->whenReady = clockEdge() + fillLatency * clockPeriod() +
-        pkt->payloadDelay;
+    blk->setWhenReady(clockEdge(fillLatency) + pkt->payloadDelay);
 
     return blk;
 }

src/mem/cache/cache_blk.hh

@@ -105,7 +105,10 @@ class CacheBlk : public ReplaceableEntry
     /** The current status of this block. @sa CacheBlockStatusBits */
     State status;
 
-    /** Which curTick() will this block be accessible */
+    /**
+     * Which curTick() will this block be accessible. Its value is only
+     * meaningful if the block is valid.
+     */
     Tick whenReady;
 
     /** Number of references to this block since it was brought in. */
@@ -114,7 +117,10 @@ class CacheBlk : public ReplaceableEntry
     /** holds the source requestor ID for this block. */
     int srcMasterId;
 
-    /** Tick on which the block was inserted in the cache. */
+    /**
+     * Tick on which the block was inserted in the cache. Its value is only
+     * meaningful if the block is valid.
+     */
     Tick tickInserted;
 
   protected:
@@ -160,7 +166,7 @@ class CacheBlk : public ReplaceableEntry
     std::list<Lock> lockList;
 
   public:
-    CacheBlk() : data(nullptr)
+    CacheBlk() : data(nullptr), tickInserted(0)
     {
         invalidate();
     }
@@ -211,7 +217,6 @@ class CacheBlk : public ReplaceableEntry
         whenReady = MaxTick;
         refCount = 0;
         srcMasterId = Request::invldMasterId;
-        tickInserted = MaxTick;
         lockList.clear();
     }
 
@@ -260,6 +265,30 @@ class CacheBlk : public ReplaceableEntry
         status |= BlkSecure;
     }
 
+    /**
+     * Get tick at which block's data will be available for access.
+     *
+     * @return Data ready tick.
+     */
+    Tick getWhenReady() const
+    {
+        return whenReady;
+    }
+
+    /**
+     * Set tick at which block's data will be available for access. The new
+     * tick must be chronologically sequential with respect to previous
+     * accesses.
+     *
+     * @param tick New data ready tick.
+     */
+    void setWhenReady(const Tick tick)
+    {
+        assert((whenReady == MaxTick) || (tick >= whenReady));
+        assert(tick >= tickInserted);
+        whenReady = tick;
+    }
+
     /**
      * Set member variables when a block insertion occurs. Resets reference
      * count to 1 (the insertion counts as a reference), and touch block if