Mem: Determine bus block size during initialisation

This patch moves the block size computation from findBlockSize to
initialisation time, once all the neighbouring ports are connected.

There is no need to dynamically update the block size, and the caching
of the value effectively avoided that anyhow. This is very similar to
what was already in place, just with a slightly leaner implementation.

src/mem/bus.cc

@@ -59,8 +59,7 @@ BaseBus::BaseBus(const BaseBusParams *p)
       headerCycles(p->header_cycles), width(p->width),
       defaultPortID(InvalidPortID),
       useDefaultRange(p->use_default_range),
-      defaultBlockSize(p->block_size),
-      cachedBlockSize(0), cachedBlockSizeValid(false)
+      blockSize(p->block_size)
 {}
 
 BaseBus::~BaseBus()
@@ -76,6 +75,34 @@ BaseBus::~BaseBus()
     }
 }
 
+void
+BaseBus::init()
+{
+    // determine the maximum peer block size, look at both the
+    // connected master and slave modules
+    uint32_t peer_block_size = 0;
+
+    for (MasterPortConstIter m = masterPorts.begin(); m != masterPorts.end();
+         ++m) {
+        peer_block_size = std::max((*m)->peerBlockSize(), peer_block_size);
+    }
+
+    for (SlavePortConstIter s = slavePorts.begin(); s != slavePorts.end();
+         ++s) {
+        peer_block_size = std::max((*s)->peerBlockSize(), peer_block_size);
+    }
+
+    // if the peers do not have a block size, use the default value
+    // set through the bus parameters
+    if (peer_block_size != 0)
+        blockSize = peer_block_size;
+
+    // check if the block size is a value known to work
+    if (blockSize != 16 || blockSize != 32 || blockSize != 64 ||
+        blockSize != 128)
+        warn_once("Block size is neither 16, 32, 64 or 128 bytes.\n");
+}
+
 MasterPort &
 BaseBus::getMasterPort(const std::string &if_name, int idx)
 {
@@ -452,34 +479,9 @@ BaseBus::getAddrRanges() const
 }
 
 unsigned
-BaseBus::findBlockSize()
+BaseBus::deviceBlockSize() const
 {
-    if (cachedBlockSizeValid)
-        return cachedBlockSize;
-
-    unsigned max_bs = 0;
-
-    for (MasterPortConstIter m = masterPorts.begin(); m != masterPorts.end();
-         ++m) {
-        unsigned tmp_bs = (*m)->peerBlockSize();
-        if (tmp_bs > max_bs)
-            max_bs = tmp_bs;
-    }
-
-    for (SlavePortConstIter s = slavePorts.begin(); s != slavePorts.end();
-         ++s) {
-        unsigned tmp_bs = (*s)->peerBlockSize();
-        if (tmp_bs > max_bs)
-            max_bs = tmp_bs;
-    }
-    if (max_bs == 0)
-        max_bs = defaultBlockSize;
-
-    if (max_bs != 64 && max_bs != 32)
-        warn_once("Blocksize found to not be 32 or 64... hmm... probably not.\n");
-    cachedBlockSize = max_bs;
-    cachedBlockSizeValid = true;
-    return max_bs;
+    return blockSize;
 }
 
 template <typename PortClass>

src/mem/bus.hh

@@ -321,11 +321,13 @@ class BaseBus : public MemObject
     Tick calcPacketTiming(PacketPtr pkt);
 
     /**
-     * Ask everyone on the bus what their size is
+     * Ask everyone on the bus what their size is and determine the
+     * bus size as either the maximum, or if no device specifies a
+     * block size return the default.
      *
-     * @return the max of all the sizes
+     * @return the max of all the sizes or the default if none is set
      */
-    unsigned findBlockSize();
+    unsigned deviceBlockSize() const;
 
     std::set<PortID> inRecvRangeChange;
 
@@ -348,9 +350,7 @@ class BaseBus : public MemObject
        addresses not handled by another port to default device. */
     const bool useDefaultRange;
 
-    const uint32_t defaultBlockSize;
-    uint32_t cachedBlockSize;
-    bool cachedBlockSizeValid;
+    uint32_t blockSize;
 
     BaseBus(const BaseBusParams *p);
 
@@ -358,6 +358,8 @@ class BaseBus : public MemObject
 
   public:
 
+    virtual void init();
+
     /** A function used to return the port associated with this bus object. */
     virtual MasterPort& getMasterPort(const std::string& if_name, int idx = -1);
     virtual SlavePort& getSlavePort(const std::string& if_name, int idx = -1);

src/mem/coherent_bus.cc

@@ -90,6 +90,9 @@ CoherentBus::CoherentBus(const CoherentBusParams *p)
 void
 CoherentBus::init()
 {
+    // the base class is responsible for determining the block size
+    BaseBus::init();
+
     // iterate over our slave ports and determine which of our
     // neighbouring master ports are snooping and add them as snoopers
     for (SlavePortConstIter p = slavePorts.begin(); p != slavePorts.end();

src/mem/coherent_bus.hh

@@ -140,7 +140,7 @@ class CoherentBus : public BaseBus
          * Get the maximum block size as seen by the bus.
          */
         virtual unsigned deviceBlockSize() const
-        { return bus.findBlockSize(); }
+        { return bus.deviceBlockSize(); }
 
     };
 
@@ -211,7 +211,7 @@ class CoherentBus : public BaseBus
         // take the max of it. This might need to be changed a bit if we ever
         // support multiple block sizes.
         virtual unsigned deviceBlockSize() const
-        { return bus.findBlockSize(); }
+        { return bus.deviceBlockSize(); }
 
     };
 

src/mem/noncoherent_bus.hh

@@ -134,7 +134,7 @@ class NoncoherentBus : public BaseBus
          * Get the maximum block size as seen by the bus.
          */
         virtual unsigned deviceBlockSize() const
-        { return bus.findBlockSize(); }
+        { return bus.deviceBlockSize(); }
 
     };
 
@@ -179,7 +179,7 @@ class NoncoherentBus : public BaseBus
          * Get the maximum block size as seen by the bus.
          */
         virtual unsigned deviceBlockSize() const
-        { return bus.findBlockSize(); }
+        { return bus.deviceBlockSize(); }
 
     };