MEM: Separate snoops and normal memory requests/responses

This patch introduces port access methods that separates snoop
request/responses from normal memory request/responses. The
differentiation is made for functional, atomic and timing accesses and
builds on the introduction of master and slave ports.

Before the introduction of this patch, the packets belonging to the
different phases of the protocol (request -> [forwarded snoop request
-> snoop response]* -> response) all use the same port access
functions, even though the snoop packets flow in the opposite
direction to the normal packet. That is, a coherent master sends
normal request and receives responses, but receives snoop requests and
sends snoop responses (vice versa for the slave). These two distinct
phases now use different access functions, as described below.

Starting with the functional access, a master sends a request to a
slave through sendFunctional, and the request packet is turned into a
response before the call returns. In a system without cache coherence,
this is all that is needed from the functional interface. For the
cache-coherent scenario, a slave also sends snoop requests to coherent
masters through sendFunctionalSnoop, with responses returned within
the same packet pointer. This is currently used by the bus and caches,
and the LSQ of the O3 CPU. The send/recvFunctional and
send/recvFunctionalSnoop are moved from the Port super class to the
appropriate subclass.

Atomic accesses follow the same flow as functional accesses, with
request being sent from master to slave through sendAtomic. In the
case of cache-coherent ports, a slave can send snoop requests to a
master through sendAtomicSnoop. Just as for the functional access
methods, the atomic send and receive member functions are moved to the
appropriate subclasses.

The timing access methods are different from the functional and atomic
in that requests and responses are separated in time and
send/recvTiming are used for both directions. Hence, a master uses
sendTiming to send a request to a slave, and a slave uses sendTiming
to send a response back to a master, at a later point in time. Snoop
requests and responses travel in the opposite direction, similar to
what happens in functional and atomic accesses. With the introduction
of this patch, it is possible to determine the direction of packets in
the bus, and no longer necessary to look for both a master and a slave
port with the requested port id.

In contrast to the normal recvFunctional, recvAtomic and recvTiming
that are pure virtual functions, the recvFunctionalSnoop,
recvAtomicSnoop and recvTimingSnoop have a default implementation that
calls panic. This is to allow non-coherent master and slave ports to
not implement these functions.

1 files changed, 37 insertions, 39 deletions

diff --git a/src/arch/x86/pagetable_walker.cc b/src/arch/x86/pagetable_walker.cc
index 87505f4df..c07af0c83 100644
--- a/src/arch/x86/pagetable_walker.cc
+++ b/src/arch/x86/pagetable_walker.cc
@@ -1,4 +1,16 @@
 /*
+ * Copyright (c) 2012 ARM Limited
+ * All rights reserved.
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
  * Copyright (c) 2007 The Hewlett-Packard Development Company
  * All rights reserved.
  *
@@ -110,49 +122,34 @@ Walker::WalkerPort::recvTiming(PacketPtr pkt)
 bool
 Walker::recvTiming(PacketPtr pkt)
 {
-    if (pkt->isResponse() || pkt->wasNacked()) {
-        WalkerSenderState * senderState =
-                dynamic_cast<WalkerSenderState *>(pkt->senderState);
-        pkt->senderState = senderState->saved;
-        WalkerState * senderWalk = senderState->senderWalk;
-        bool walkComplete = senderWalk->recvPacket(pkt);
-        delete senderState;
-        if (walkComplete) {
-            std::list<WalkerState *>::iterator iter;
-            for (iter = currStates.begin(); iter != currStates.end(); iter++) {
-                WalkerState * walkerState = *(iter);
-                if (walkerState == senderWalk) {
-                    iter = currStates.erase(iter);
-                    break;
-                }
-            }
-            delete senderWalk;
-            // Since we block requests when another is outstanding, we
-            // need to check if there is a waiting request to be serviced
-            if (currStates.size()) {
-                WalkerState * newState = currStates.front();
-                if (!newState->wasStarted())
-                    newState->startWalk();
+    assert(pkt->isResponse());
+    WalkerSenderState * senderState =
+        dynamic_cast<WalkerSenderState *>(pkt->senderState);
+    pkt->senderState = senderState->saved;
+    WalkerState * senderWalk = senderState->senderWalk;
+    bool walkComplete = senderWalk->recvPacket(pkt);
+    delete senderState;
+    if (walkComplete) {
+        std::list<WalkerState *>::iterator iter;
+        for (iter = currStates.begin(); iter != currStates.end(); iter++) {
+            WalkerState * walkerState = *(iter);
+            if (walkerState == senderWalk) {
+                iter = currStates.erase(iter);
+                break;
             }
         }
-    } else {
-        DPRINTF(PageTableWalker, "Received strange packet\n");
+        delete senderWalk;
+        // Since we block requests when another is outstanding, we
+        // need to check if there is a waiting request to be serviced
+        if (currStates.size()) {
+            WalkerState * newState = currStates.front();
+            if (!newState->wasStarted())
+                newState->startWalk();
+        }
     }
     return true;
 }
 
-Tick
-Walker::WalkerPort::recvAtomic(PacketPtr pkt)
-{
-    return 0;
-}
-
-void
-Walker::WalkerPort::recvFunctional(PacketPtr pkt)
-{
-    return;
-}
-
 void
 Walker::WalkerPort::recvRetry()
 {
@@ -572,7 +569,8 @@ Walker::WalkerState::setupWalk(Addr vaddr)
 bool
 Walker::WalkerState::recvPacket(PacketPtr pkt)
 {
-    if (pkt->isResponse() && !pkt->wasNacked()) {
+    assert(pkt->isResponse());
+    if (!pkt->wasNacked()) {
         assert(inflight);
         assert(state == Waiting);
         assert(!read);
@@ -615,7 +613,7 @@ Walker::WalkerState::recvPacket(PacketPtr pkt)
             }
             return true;
         }
-    } else if (pkt->wasNacked()) {
+    } else {
         DPRINTF(PageTableWalker, "Request was nacked. Entering retry state\n");
         pkt->reinitNacked();
         if (!walker->sendTiming(this, pkt)) {