stream: Add flow control API

Add basic flow control to stream. A stream slave may return short, indicating
that it is not capable of accepting any more data at the present time. Polling
or a callback can be used via the can_push() function to determine when the
slave can receive again.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>

3 files changed, 18 insertions, 6 deletions

diff --git a/hw/core/stream.c b/hw/core/stream.c
index a07d6a56d3..5397a8d74a 100644
--- a/hw/core/stream.c
+++ b/hw/core/stream.c
@@ -1,11 +1,20 @@
 #include "hw/stream.h"
 
-void
+size_t
 stream_push(StreamSlave *sink, uint8_t *buf, size_t len, uint32_t *app)
 {
     StreamSlaveClass *k =  STREAM_SLAVE_GET_CLASS(sink);
 
-    k->push(sink, buf, len, app);
+    return k->push(sink, buf, len, app);
+}
+
+bool
+stream_can_push(StreamSlave *sink, StreamCanPushNotifyFn notify,
+                void *notify_opaque)
+{
+    StreamSlaveClass *k =  STREAM_SLAVE_GET_CLASS(sink);
+
+    return k->can_push ? k->can_push(sink, notify, notify_opaque) : true;
 }
 
 static const TypeInfo stream_slave_info = {
diff --git a/hw/dma/xilinx_axidma.c b/hw/dma/xilinx_axidma.c
index 2bbfea1503..80ce57fca2 100644
--- a/hw/dma/xilinx_axidma.c
+++ b/hw/dma/xilinx_axidma.c
@@ -381,7 +381,7 @@ static void xilinx_axidma_reset(DeviceState *dev)
     }
 }
 
-static void
+static size_t
 xilinx_axidma_data_stream_push(StreamSlave *obj, unsigned char *buf, size_t len,
                                uint32_t *app)
 {
@@ -393,6 +393,7 @@ xilinx_axidma_data_stream_push(StreamSlave *obj, unsigned char *buf, size_t len,
     }
     stream_process_s2mem(s, buf, len, app);
     stream_update_irq(s);
+    return len;
 }
 
 static uint64_t axidma_read(void *opaque, hwaddr addr,
diff --git a/hw/net/xilinx_axienet.c b/hw/net/xilinx_axienet.c
index f4638b2fdf..6d27546b29 100644
--- a/hw/net/xilinx_axienet.c
+++ b/hw/net/xilinx_axienet.c
@@ -815,7 +815,7 @@ static void eth_cleanup(NetClientState *nc)
     g_free(s);
 }
 
-static void
+static size_t
 xilinx_axienet_data_stream_push(StreamSlave *obj, uint8_t *buf, size_t size,
                                 uint32_t *hdr)
 {
@@ -824,13 +824,13 @@ xilinx_axienet_data_stream_push(StreamSlave *obj, uint8_t *buf, size_t size,
 
     /* TX enable ?  */
     if (!(s->tc & TC_TX)) {
-        return;
+        return size;
     }
 
     /* Jumbo or vlan sizes ?  */
     if (!(s->tc & TC_JUM)) {
         if (size > 1518 && size <= 1522 && !(s->tc & TC_VLAN)) {
-            return;
+            return size;
         }
     }
 
@@ -858,6 +858,8 @@ xilinx_axienet_data_stream_push(StreamSlave *obj, uint8_t *buf, size_t size,
     s->stats.tx_bytes += size;
     s->regs[R_IS] |= IS_TX_COMPLETE;
     enet_update_irq(s);
+
+    return size;
 }
 
 static NetClientInfo net_xilinx_enet_info = {