dev: Remove zero-time loop in DMA timing send

This patch removes the zero-time loop used to send items from the DMA
port transmit list. Instead of having a loop, the DMA port now uses an
event to schedule sending of a single packet.

Ultimately this patch serves to ease the transition to a blocking
4-phase handshake.

A follow-on patch will update the regression statistics.

1 files changed, 41 insertions, 19 deletions

diff --git a/src/dev/dma_device.hh b/src/dev/dma_device.hh
index c46fbfd76..cd328f3d6 100644
--- a/src/dev/dma_device.hh
+++ b/src/dev/dma_device.hh
@@ -51,7 +51,37 @@
 
 class DmaPort : public MasterPort
 {
-  protected:
+  private:
+
+    /**
+     * Take the first packet of the transmit list and attempt to send
+     * it as a timing request. If it is successful, schedule the
+     * sending of the next packet, otherwise remember that we are
+     * waiting for a retry.
+     */
+    void trySendTimingReq();
+
+    /**
+     * For timing, attempt to send the first item on the transmit
+     * list, and if it is successful and there are more packets
+     * waiting, then schedule the sending of the next packet. For
+     * atomic, simply send and process everything on the transmit
+     * list.
+     */
+    void sendDma();
+
+    /**
+     * Handle a response packet by updating the corresponding DMA
+     * request state to reflect the bytes received, and also update
+     * the pending request counter. If the DMA request that this
+     * packet is part of is complete, then signal the completion event
+     * if present, potentially with a delay added to it.
+     *
+     * @param pkt Response packet to handler
+     * @param delay Additional delay for scheduling the completion event
+     */
+    void handleResp(PacketPtr pkt, Tick delay = 0);
+
     struct DmaReqState : public Packet::SenderState
     {
         /** Event to call on the device when this transaction (all packets)
@@ -59,30 +89,34 @@ class DmaPort : public MasterPort
         Event *completionEvent;
 
         /** Total number of bytes that this transaction involves. */
-        Addr totBytes;
+        const Addr totBytes;
 
         /** Number of bytes that have been acked for this transaction. */
         Addr numBytes;
 
         /** Amount to delay completion of dma by */
-        Tick delay;
+        const Tick delay;
 
         DmaReqState(Event *ce, Addr tb, Tick _delay)
             : completionEvent(ce), totBytes(tb), numBytes(0), delay(_delay)
         {}
     };
 
+    /** The device that owns this port. */
     MemObject *device;
 
-    /** Use a deque as we never to any insertion or removal in the middle */
+    /** Use a deque as we never do any insertion or removal in the middle */
     std::deque<PacketPtr> transmitList;
 
+    /** Event used to schedule a future sending from the transmit list. */
+    EventWrapper<DmaPort, &DmaPort::sendDma> sendEvent;
+
     /** The system that device/port are in. This is used to select which mode
      * we are currently operating in. */
     System *sys;
 
     /** Id for all requests */
-    MasterID masterId;
+    const MasterID masterId;
 
     /** Number of outstanding packets the dma port has. */
     uint32_t pendingCount;
@@ -95,23 +129,12 @@ class DmaPort : public MasterPort
      * send whatever it is that it's sending. */
     bool inRetry;
 
-    /**
-     * Handle a response packet by updating the corresponding DMA
-     * request state to reflect the bytes received, and also update
-     * the pending request counter. If the DMA request that this
-     * packet is part of is complete, then signal the completion event
-     * if present, potentially with a delay added to it.
-     *
-     * @param pkt Response packet to handler
-     * @param delay Additional delay for scheduling the completion event
-     */
-    void handleResp(PacketPtr pkt, Tick delay = 0);
+  protected:
 
     bool recvTimingResp(PacketPtr pkt);
     void recvRetry() ;
 
     void queueDma(PacketPtr pkt);
-    void sendDma();
 
   public:
 
@@ -148,7 +171,7 @@ class DmaDevice : public PioDevice
         dmaPort.dmaAction(MemCmd::ReadReq, addr, size, event, data, delay);
     }
 
-    bool dmaPending() { return dmaPort.dmaPending(); }
+    bool dmaPending() const { return dmaPort.dmaPending(); }
 
     virtual void init();
 
@@ -159,7 +182,6 @@ class DmaDevice : public PioDevice
     virtual BaseMasterPort &getMasterPort(const std::string &if_name,
                                           PortID idx = InvalidPortID);
 
-    friend class DmaPort;
 };
 
 #endif // __DEV_DMA_DEVICE_HH__