Packet: Cleaning up packet command and attribute

This patch removes unused commands and attributes from the packet to
avoid any confusion. It is part of an effort to clear up how and where
different commands and attributes are used.

src/mem/packet.cc

@@ -98,11 +98,11 @@ MemCmd::commandInfo[] =
     /* HardPFResp */
     { SET4(IsRead, IsResponse, IsHWPrefetch, HasData),
             InvalidCmd, "HardPFResp" },
-    /* WriteInvalidateReq */
+    /* WriteInvalidateReq (currently unused, see packet.hh) */
     { SET6(IsWrite, NeedsExclusive, IsInvalidate,
            IsRequest, HasData, NeedsResponse),
             WriteInvalidateResp, "WriteInvalidateReq" },
-    /* WriteInvalidateResp */
+    /* WriteInvalidateResp (currently unused, see packet.hh) */
     { SET3(IsWrite, NeedsExclusive, IsResponse),
             InvalidCmd, "WriteInvalidateResp" },
     /* UpgradeReq */

src/mem/packet.hh

@@ -91,6 +91,14 @@ class MemCmd
         HardPFReq,
         SoftPFResp,
         HardPFResp,
+        // WriteInvalidateReq transactions used to be generated by the
+        // DMA ports when writing full blocks to memory, however, it
+        // is not used anymore since we put the I/O cache in place to
+        // deal with partial block writes. Hence, WriteInvalidateReq
+        // and WriteInvalidateResp are currently unused. The
+        // implication is that the I/O cache does read-exclusive
+        // operations on every full-cache-block DMA, and ultimately
+        // this needs to be fixed.
         WriteInvalidateReq,
         WriteInvalidateResp,
         UpgradeReq,
@@ -133,7 +141,6 @@ class MemCmd
         IsRead,         //!< Data flows from responder to requester
         IsWrite,        //!< Data flows from requester to responder
         IsUpgrade,
-        IsPrefetch,     //!< Not a demand access
         IsInvalidate,
         NeedsExclusive, //!< Requires exclusive copy to complete in-cache
         IsRequest,      //!< Issued by requester