mem: write streaming support via WriteInvalidate promotion

Support full-block writes directly rather than requiring RMW:
 * a cache line is allocated in the cache upon receipt of a
   WriteInvalidateReq, not the WriteInvalidateResp.
 * only top-level caches allocate the line; the others just pass
   the request along and invalidate as necessary.
 * to close a timing window between the *Req and the *Resp, a new
   metadata bit tracks whether another cache has read a copy of
   the new line before the writeback to memory.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mem/cache/blk.hh b/src/mem/cache/blk.hh
index 626b4818d..ff09b42c4 100644
--- a/src/mem/cache/blk.hh
+++ b/src/mem/cache/blk.hh
@@ -72,7 +72,10 @@ enum CacheBlkStatusBits {
     /** block was a hardware prefetch yet unaccessed*/
     BlkHWPrefetched =   0x20,
     /** block holds data from the secure memory space */
-    BlkSecure =         0x40
+    BlkSecure =         0x40,
+    /** can the block transition to E? (hasn't been shared with another cache)
+      * used to close a timing gap when handling WriteInvalidate packets */
+    BlkCanGoExclusive = 0x80
 };
 
 /**