mem: Co-ordination of CMOs in the xbar

A clean packet request serving a cache maintenance operation (CMO)
visits all memories down to the specified xbar. The visited caches
invalidate their copy (if the CMO is invalidating) and if a dirty copy
is found a write packet writes the dirty data to the memory level
below the specified xbar. A response is send back when all the caches
are clean and/or invalidated and the specified xbar has seen the write
packet.

This patch adds the following functionality in the xbar:
1) Accounts for the cache clean requests that go through the xbar
2) Generates the cache clean response when both the cache clean
request and the corresponding writeclean packet has crossed the
destination xbar.

Previously transactions in the xbar were identified using the pointer
of the original request. Cache clean transactions comprise of two
different packets, the clean request and the writeclean, and therefore
have different request pointers. This patch adds support for custom
transaction IDs that by default take the value of the request pointer
but can be overriden by the contructor. This allows the clean request
and writeclean share the same id which the coherent xbar uses to
co-ordinate them and send the response in a timely manner.

Change-Id: I80db76386a1caded38dc66e6e18f930c3bb800ff
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5051
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index 88829d358..66625b382 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -70,6 +70,7 @@ class Packet;
 typedef Packet *PacketPtr;
 typedef uint8_t* PacketDataPtr;
 typedef std::list<PacketPtr> PacketList;
+typedef uint64_t PacketId;
 
 class MemCmd
 {
@@ -316,6 +317,8 @@ class Packet : public Printable
     /// The command field of the packet.
     MemCmd cmd;
 
+    const PacketId id;
+
     /// A pointer to the original request.
     const RequestPtr req;
 
@@ -743,9 +746,9 @@ class Packet : public Printable
      * not be valid. The command must be supplied.
      */
     Packet(const RequestPtr _req, MemCmd _cmd)
-        :  cmd(_cmd), req(_req), data(nullptr), addr(0), _isSecure(false),
-           size(0), headerDelay(0), snoopDelay(0), payloadDelay(0),
-           senderState(NULL)
+        :  cmd(_cmd), id((PacketId)_req), req(_req), data(nullptr), addr(0),
+           _isSecure(false), size(0), headerDelay(0), snoopDelay(0),
+           payloadDelay(0), senderState(NULL)
     {
         if (req->hasPaddr()) {
             addr = req->getPaddr();
@@ -763,10 +766,10 @@ class Packet : public Printable
      * a request that is for a whole block, not the address from the
      * req.  this allows for overriding the size/addr of the req.
      */
-    Packet(const RequestPtr _req, MemCmd _cmd, int _blkSize)
-        :  cmd(_cmd), req(_req), data(nullptr), addr(0), _isSecure(false),
-           headerDelay(0), snoopDelay(0), payloadDelay(0),
-           senderState(NULL)
+    Packet(const RequestPtr _req, MemCmd _cmd, int _blkSize, PacketId _id = 0)
+        :  cmd(_cmd), id(_id ? _id : (PacketId)_req), req(_req), data(nullptr),
+           addr(0), _isSecure(false), headerDelay(0), snoopDelay(0),
+           payloadDelay(0), senderState(NULL)
     {
         if (req->hasPaddr()) {
             addr = req->getPaddr() & ~(_blkSize - 1);
@@ -785,7 +788,7 @@ class Packet : public Printable
      * packet should allocate its own data.
      */
     Packet(const PacketPtr pkt, bool clear_flags, bool alloc_data)
-        :  cmd(pkt->cmd), req(pkt->req),
+        :  cmd(pkt->cmd), id(pkt->id), req(pkt->req),
            data(nullptr),
            addr(pkt->addr), _isSecure(pkt->_isSecure), size(pkt->size),
            bytesValid(pkt->bytesValid),