ARM: Don't return the result of a table walk the same cycle it's completed.

The L1 cache may have been accessed to provide this data, which confuses
it, if it ends up being accesses twice in one cycle. Instead wait 1 tick
which will force the timing simple CPU to forward to its next clock cycle
when the translation completes.

Also prevent multiple outstanding table walks from occuring at once.

src/arch/arm/table_walker.cc

@@ -41,13 +41,14 @@
 #include "arch/arm/table_walker.hh"
 #include "arch/arm/tlb.hh"
 #include "dev/io_device.hh"
+#include "cpu/base.hh"
 #include "cpu/thread_context.hh"
 
 using namespace ArmISA;
 
 TableWalker::TableWalker(const Params *p)
-    : MemObject(p), port(NULL), tlb(NULL),
-      currState(NULL), doL1DescEvent(this), doL2DescEvent(this)
+    : MemObject(p), port(NULL), tlb(NULL), currState(NULL), pending(false),
+      doL1DescEvent(this), doL2DescEvent(this), doProcessEvent(this)
 {
     sctlr = 0;
 }
@@ -115,6 +116,35 @@ TableWalker::walk(RequestPtr _req, ThreadContext *_tc, uint8_t _cid, TLB::Mode _
     currState->isFetch = (currState->mode == TLB::Execute);
     currState->isWrite = (currState->mode == TLB::Write);
 
+
+    if (!currState->timing)
+        return processWalk();
+
+    if (pending) {
+        pendingQueue.push_back(currState);
+        currState = NULL;
+    } else {
+        pending = true;
+        processWalk();
+    }
+
+    return NoFault;
+}
+
+void
+TableWalker::processWalkWrapper()
+{
+    assert(!currState);
+    assert(pendingQueue.size());
+    currState = pendingQueue.front();
+    pendingQueue.pop_front();
+    pending = true;
+    processWalk();
+}
+
+Fault
+TableWalker::processWalk()
+{
     Addr ttbr = 0;
 
     // If translation isn't enabled, we shouldn't be here
@@ -146,6 +176,9 @@ TableWalker::walk(RequestPtr _req, ThreadContext *_tc, uint8_t _cid, TLB::Mode _
         if (currState->timing) {
             currState->transState->finish(f, currState->req,
                                           currState->tc, currState->mode);
+
+            pending = false;
+            nextWalk(currState->tc);
             currState = NULL;
         } else {
             currState->tc = NULL;
@@ -156,7 +189,8 @@ TableWalker::walk(RequestPtr _req, ThreadContext *_tc, uint8_t _cid, TLB::Mode _
 
     if (currState->timing) {
         port->dmaAction(MemCmd::ReadReq, l1desc_addr, sizeof(uint32_t),
-                &doL1DescEvent, (uint8_t*)&currState->l1Desc.data, (Tick)0);
+                &doL1DescEvent, (uint8_t*)&currState->l1Desc.data,
+                currState->tc->getCpuPtr()->ticks(1));
         DPRINTF(TLBVerbose, "Adding to walker fifo: queue size before adding: %d\n",
                 stateQueueL1.size());
         stateQueueL1.push_back(currState);
@@ -167,7 +201,8 @@ TableWalker::walk(RequestPtr _req, ThreadContext *_tc, uint8_t _cid, TLB::Mode _
            flag = Request::UNCACHEABLE;
         }
         port->dmaAction(MemCmd::ReadReq, l1desc_addr, sizeof(uint32_t),
-                NULL, (uint8_t*)&currState->l1Desc.data, (Tick)0, flag);
+                NULL, (uint8_t*)&currState->l1Desc.data,
+                currState->tc->getCpuPtr()->ticks(1), flag);
         doL1Descriptor();
         f = currState->fault;
     }
@@ -498,10 +533,12 @@ TableWalker::doL1Descriptor()
         if (currState->timing) {
             currState->delayed = true;
             port->dmaAction(MemCmd::ReadReq, l2desc_addr, sizeof(uint32_t),
-                    &doL2DescEvent, (uint8_t*)&currState->l2Desc.data, 0);
+                    &doL2DescEvent, (uint8_t*)&currState->l2Desc.data,
+                    currState->tc->getCpuPtr()->ticks(1));
         } else {
             port->dmaAction(MemCmd::ReadReq, l2desc_addr, sizeof(uint32_t),
-                    NULL, (uint8_t*)&currState->l2Desc.data, 0);
+                    NULL, (uint8_t*)&currState->l2Desc.data,
+                    currState->tc->getCpuPtr()->ticks(1));
             doL2Descriptor();
         }
         return;
@@ -589,6 +626,9 @@ TableWalker::doL1DescriptorWrapper()
         currState->transState->finish(currState->fault, currState->req,
                                       currState->tc, currState->mode);
 
+        pending = false;
+        nextWalk(currState->tc);
+
         currState->req = NULL;
         currState->tc = NULL;
         currState->delayed = false;
@@ -600,10 +640,12 @@ TableWalker::doL1DescriptorWrapper()
         currState->fault = tlb->translateTiming(currState->req, currState->tc,
                                        currState->transState, currState->mode);
 
+        pending = false;
+        nextWalk(currState->tc);
+
         currState->req = NULL;
         currState->tc = NULL;
         currState->delayed = false;
-
         delete currState;
     } else {
         // need to do L2 descriptor
@@ -633,15 +675,28 @@ TableWalker::doL2DescriptorWrapper()
                                       currState->transState, currState->mode);
     }
 
+
+    stateQueueL2.pop_front();
+    pending = false;
+    nextWalk(currState->tc);
+
     currState->req = NULL;
     currState->tc = NULL;
     currState->delayed = false;
 
-    stateQueueL2.pop_front();
     delete currState;
     currState = NULL;
 }
 
+void
+TableWalker::nextWalk(ThreadContext *tc)
+{
+    if (pendingQueue.size())
+        schedule(doProcessEvent, tc->getCpuPtr()->nextCycle(curTick+1));
+}
+
+
+
 ArmISA::TableWalker *
 ArmTableWalkerParams::create()
 {

src/arch/arm/table_walker.hh

@@ -320,6 +320,11 @@ class TableWalker : public MemObject
      * require an additional level. */
     std::list<WalkerState *> stateQueueL2;
 
+    /** Queue of requests that have passed are waiting because the walker is
+     * currently busy. */
+    std::list<WalkerState *> pendingQueue;;
+
+
     /** Port to issue translation requests from */
     DmaPort *port;
 
@@ -331,6 +336,9 @@ class TableWalker : public MemObject
 
     WalkerState *currState;
 
+    /** If a timing translation is currently in progress */
+    bool pending;
+
   public:
     typedef ArmTableWalkerParams Params;
     TableWalker(const Params *p);
@@ -362,7 +370,11 @@ class TableWalker : public MemObject
     void doL2DescriptorWrapper();
     EventWrapper<TableWalker, &TableWalker::doL2DescriptorWrapper> doL2DescEvent;
 
+    Fault processWalk();
+    void processWalkWrapper();
+    EventWrapper<TableWalker, &TableWalker::processWalkWrapper> doProcessEvent;
 
+    void nextWalk(ThreadContext *tc);
 };