mem: Split port retry for all different packet classes

This patch fixes a long-standing isue with the port flow
control. Before this patch the retry mechanism was shared between all
different packet classes. As a result, a snoop response could get
stuck behind a request waiting for a retry, even if the send/recv
functions were split. This caused message-dependent deadlocks in
stress-test scenarios.

The patch splits the retry into one per packet (message) class. Thus,
sendTimingReq has a corresponding recvReqRetry, sendTimingResp has
recvRespRetry etc. Most of the changes to the code involve simply
clarifying what type of request a specific object was accepting.

The biggest change in functionality is in the cache downstream packet
queue, facing the memory. This queue was shared by requests and snoop
responses, and it is now split into two queues, each with their own
flow control, but the same physical MasterPort. These changes fixes
the previously seen deadlocks.

1 files changed, 32 insertions, 16 deletions

diff --git a/src/mem/port.hh b/src/mem/port.hh
index 6b5e9530c..0d88441dc 100644
--- a/src/mem/port.hh
+++ b/src/mem/port.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2012 ARM Limited
+ * Copyright (c) 2011-2012,2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -214,7 +214,7 @@ class MasterPort : public BaseMasterPort
      * Attempt to send a timing request to the slave port by calling
      * its corresponding receive function. If the send does not
      * succeed, as indicated by the return value, then the sender must
-     * wait for a recvRetry at which point it can re-issue a
+     * wait for a recvReqRetry at which point it can re-issue a
      * sendTimingReq.
      *
      * @param pkt Packet to send.
@@ -227,8 +227,8 @@ class MasterPort : public BaseMasterPort
      * Attempt to send a timing snoop response packet to the slave
      * port by calling its corresponding receive function. If the send
      * does not succeed, as indicated by the return value, then the
-     * sender must wait for a recvRetry at which point it can re-issue
-     * a sendTimingSnoopResp.
+     * sender must wait for a recvRetrySnoop at which point it can
+     * re-issue a sendTimingSnoopResp.
      *
      * @param pkt Packet to send.
      */
@@ -236,9 +236,11 @@ class MasterPort : public BaseMasterPort
 
     /**
      * Send a retry to the slave port that previously attempted a
-     * sendTimingResp to this master port and failed.
+     * sendTimingResp to this master port and failed. Note that this
+     * is virtual so that the "fake" snoop response port in the
+     * coherent crossbar can override the behaviour.
      */
-    virtual void sendRetry();
+    virtual void sendRetryResp();
 
     /**
      * Determine if this master port is snooping or not. The default
@@ -294,12 +296,21 @@ class MasterPort : public BaseMasterPort
     }
 
     /**
-     * Called by the slave port if sendTimingReq or
-     * sendTimingSnoopResp was called on this master port (causing
-     * recvTimingReq and recvTimingSnoopResp to be called on the
-     * slave port) and was unsuccesful.
+     * Called by the slave port if sendTimingReq was called on this
+     * master port (causing recvTimingReq to be called on the slave
+     * port) and was unsuccesful.
      */
-    virtual void recvRetry() = 0;
+    virtual void recvReqRetry() = 0;
+
+    /**
+     * Called by the slave port if sendTimingSnoopResp was called on this
+     * master port (causing recvTimingSnoopResp to be called on the slave
+     * port) and was unsuccesful.
+     */
+    virtual void recvRetrySnoopResp()
+    {
+        panic("%s was not expecting a snoop retry\n", name());
+    }
 
     /**
      * Called to receive an address range change from the peer slave
@@ -356,7 +367,7 @@ class SlavePort : public BaseSlavePort
      * Attempt to send a timing response to the master port by calling
      * its corresponding receive function. If the send does not
      * succeed, as indicated by the return value, then the sender must
-     * wait for a recvRetry at which point it can re-issue a
+     * wait for a recvRespRetry at which point it can re-issue a
      * sendTimingResp.
      *
      * @param pkt Packet to send.
@@ -376,10 +387,15 @@ class SlavePort : public BaseSlavePort
 
     /**
      * Send a retry to the master port that previously attempted a
-     * sendTimingReq or sendTimingSnoopResp to this slave port and
-     * failed.
+     * sendTimingReq to this slave port and failed.
+     */
+    void sendRetryReq();
+
+    /**
+     * Send a retry to the master port that previously attempted a
+     * sendTimingSnoopResp to this slave port and failed.
      */
-    void sendRetry();
+    void sendRetrySnoopResp();
 
     /**
      * Find out if the peer master port is snooping or not.
@@ -448,7 +464,7 @@ class SlavePort : public BaseSlavePort
      * slave port (causing recvTimingResp to be called on the master
      * port) and was unsuccesful.
      */
-    virtual void recvRetry() = 0;
+    virtual void recvRespRetry() = 0;
 
 };