Packet: Remove NACKs from packet and its use in endpoints

This patch removes the NACK frrom the packet as there is no longer any
module in the system that issues them (the bridge was the only one and
the previous patch removes that).

The handling of NACKs was mostly avoided throughout the code base, by
using e.g. panic or assert false, but in a few locations the NACKs
were actually dealt with (although NACKs never occured in any of the
regressions). Most notably, the DMA port will now never receive a NACK
and the backoff time is thus never changed. As a consequence, the
entire backoff mechanism (similar to a PCI bus) is now removed and the
DMA port entirely relies on the bus performing the arbitration and
issuing a retry when appropriate. This is more in line with e.g. PCIe.

Surprisingly, this patch has no impact on any of the regressions. As
mentioned in the patch that removes the NACK from the bridge, a
follow-up patch should change the request and response buffer size for
at least one regression to also verify that the system behaves as
expected when the bridge fills up.

3 files changed, 0 insertions, 39 deletions

diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh
index 4d8adbd90..2fdbc5c1d 100644
--- a/src/mem/cache/cache_impl.hh
+++ b/src/mem/cache/cache_impl.hh
@@ -692,8 +692,6 @@ Cache<TagStore>::atomicAccess(PacketPtr pkt)
         DPRINTF(Cache, "Receive response: %s for addr %x in state %i\n",
                 bus_pkt->cmdString(), bus_pkt->getAddr(), old_state);
 
-        assert(!bus_pkt->wasNacked());
-
         // If packet was a forward, the response (if any) is already
         // in place in the bus_pkt == pkt structure, so we don't need
         // to do anything.  Otherwise, use the separate bus_pkt to
@@ -823,12 +821,6 @@ Cache<TagStore>::handleResponse(PacketPtr pkt)
 
     assert(mshr);
 
-    if (pkt->wasNacked()) {
-        //pkt->reinitFromRequest();
-        warn("NACKs from devices not connected to the same bus "
-             "not implemented\n");
-        return;
-    }
     if (is_error) {
         DPRINTF(Cache, "Cache received packet with error for address %x, "
                 "cmd: %s\n", pkt->getAddr(), pkt->cmdString());
@@ -1644,12 +1636,6 @@ template<class TagStore>
 bool
 Cache<TagStore>::MemSidePort::recvTimingResp(PacketPtr pkt)
 {
-    // this needs to be fixed so that the cache updates the mshr and sends the
-    // packet back out on the link, but it probably won't happen so until this
-    // gets fixed, just panic when it does
-    if (pkt->wasNacked())
-        panic("Need to implement cache resending nacked packets!\n");
-
     cache->handleResponse(pkt);
     return true;
 }
diff --git a/src/mem/packet.cc b/src/mem/packet.cc
index 69cf36a5c..dc5ff4362 100644
--- a/src/mem/packet.cc
+++ b/src/mem/packet.cc
@@ -154,8 +154,6 @@ MemCmd::commandInfo[] =
         MessageResp, "MessageReq" },
     /* IntResp -- for interrupts */
     { SET2(IsWrite, IsResponse), InvalidCmd, "MessageResp" },
-    /* NetworkNackError  -- nacked at network layer (not by protocol) */
-    { SET2(IsResponse, IsError), InvalidCmd, "NetworkNackError" },
     /* InvalidDestError  -- packet dest field invalid */
     { SET2(IsResponse, IsError), InvalidCmd, "InvalidDestError" },
     /* BadAddressError   -- memory address invalid */
diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index cdcefcadb..7396048d6 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -120,7 +120,6 @@ class MemCmd
         // @TODO these should be classified as responses rather than
         // requests; coding them as requests initially for backwards
         // compatibility
-        NetworkNackError,  // nacked at network layer (not by protocol)
         InvalidDestError,  // packet dest field invalid
         BadAddressError,   // memory address invalid
         FunctionalReadError, // unable to fulfill functional read
@@ -466,20 +465,12 @@ class Packet : public Printable
     // their encoding keeps changing (from result field to command
     // field, etc.)
     void
-    setNacked()
-    {
-        assert(isResponse());
-        cmd = MemCmd::NetworkNackError;
-    }
-
-    void
     setBadAddress()
     {
         assert(isResponse());
         cmd = MemCmd::BadAddressError;
     }
 
-    bool wasNacked() const     { return cmd == MemCmd::NetworkNackError; }
     bool hadBadAddress() const { return cmd == MemCmd::BadAddressError; }
     void copyError(Packet *pkt) { assert(pkt->isError()); cmd = pkt->cmd; }
 
@@ -669,20 +660,6 @@ class Packet : public Printable
         }
     }
 
-    /**
-     * Take a request packet that has been returned as NACKED and
-     * modify it so that it can be sent out again. Only packets that
-     * need a response can be NACKED, so verify that that is true.
-     */
-    void
-    reinitNacked()
-    {
-        assert(wasNacked());
-        cmd = origCmd;
-        assert(needsResponse());
-        clearDest();
-    }
-
     void
     setSize(unsigned size)
     {