xilinx_axienet/dma: Implement rx path flow control

Implement flow control for the RX data path from xilinx_axienet->xilinx_axidma.
On short return from axidma, then ethernet sets up the notify callback to resume
transfer from where it left off.

This also allows the ethernet to track whether there is an in progress transaction
and return false from ethernet can_receive() as appropriate.

If the DMA backs up or is disabled it waits for enablement. When the rx stream IO
region is touched, the can_push() notify function is called if set.

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

hw/dma/xilinx_axidma.c

@@ -117,6 +117,9 @@ struct XilinxAXIDMA {
     XilinxAXIDMAStreamSlave rx_data_dev;
 
     struct Stream streams[2];
+
+    StreamCanPushNotifyFn notify;
+    void *notify_opaque;
 };
 
 /*
@@ -315,16 +318,16 @@ static void stream_process_mem2s(struct Stream *s,
     }
 }
 
-static void stream_process_s2mem(struct Stream *s,
-                                 unsigned char *buf, size_t len, uint32_t *app)
+static size_t stream_process_s2mem(struct Stream *s, unsigned char *buf,
+                                   size_t len, uint32_t *app)
 {
     uint32_t prev_d;
     unsigned int rxlen;
-    int pos = 0;
+    size_t pos = 0;
     int sof = 1;
 
     if (!stream_running(s) || stream_idle(s)) {
-        return;
+        return 0;
     }
 
     while (len) {
@@ -369,6 +372,8 @@ static void stream_process_s2mem(struct Stream *s,
             break;
         }
     }
+
+    return pos;
 }
 
 static void xilinx_axidma_reset(DeviceState *dev)
@@ -381,19 +386,37 @@ static void xilinx_axidma_reset(DeviceState *dev)
     }
 }
 
+static bool
+xilinx_axidma_data_stream_can_push(StreamSlave *obj,
+                                   StreamCanPushNotifyFn notify,
+                                   void *notify_opaque)
+{
+    XilinxAXIDMAStreamSlave *ds = XILINX_AXI_DMA_DATA_STREAM(obj);
+    struct Stream *s = &ds->dma->streams[1];
+
+    if (!stream_running(s) || stream_idle(s)) {
+        ds->dma->notify = notify;
+        ds->dma->notify_opaque = notify_opaque;
+        return false;
+    }
+
+    return true;
+}
+
 static size_t
 xilinx_axidma_data_stream_push(StreamSlave *obj, unsigned char *buf, size_t len,
                                uint32_t *app)
 {
     XilinxAXIDMAStreamSlave *ds = XILINX_AXI_DMA_DATA_STREAM(obj);
     struct Stream *s = &ds->dma->streams[1];
+    size_t ret;
 
     if (!app) {
         hw_error("No stream app data!\n");
     }
-    stream_process_s2mem(s, buf, len, app);
+    ret = stream_process_s2mem(s, buf, len, app);
     stream_update_irq(s);
-    return len;
+    return ret;
 }
 
 static uint64_t axidma_read(void *opaque, hwaddr addr,
@@ -481,6 +504,10 @@ static void axidma_write(void *opaque, hwaddr addr,
             s->regs[addr] = value;
             break;
     }
+    if (sid == 1 && d->notify) {
+        d->notify(d->notify_opaque);
+        d->notify = NULL;
+    }
     stream_update_irq(s);
 }
 
@@ -558,11 +585,17 @@ static void axidma_class_init(ObjectClass *klass, void *data)
     dc->props = axidma_properties;
 }
 
+static StreamSlaveClass xilinx_axidma_data_stream_class = {
+    .push = xilinx_axidma_data_stream_push,
+    .can_push = xilinx_axidma_data_stream_can_push,
+};
+
 static void xilinx_axidma_stream_class_init(ObjectClass *klass, void *data)
 {
     StreamSlaveClass *ssc = STREAM_SLAVE_CLASS(klass);
 
-    ssc->push = data;
+    ssc->push = ((StreamSlaveClass *)data)->push;
+    ssc->can_push = ((StreamSlaveClass *)data)->can_push;
 }
 
 static const TypeInfo axidma_info = {
@@ -578,7 +611,7 @@ static const TypeInfo xilinx_axidma_data_stream_info = {
     .parent        = TYPE_OBJECT,
     .instance_size = sizeof(struct XilinxAXIDMAStreamSlave),
     .class_init    = xilinx_axidma_stream_class_init,
-    .class_data    = xilinx_axidma_data_stream_push,
+    .class_data    = &xilinx_axidma_data_stream_class,
     .interfaces = (InterfaceInfo[]) {
         { TYPE_STREAM_SLAVE },
         { }

hw/net/xilinx_axienet.c

@@ -383,6 +383,9 @@ struct XilinxAXIEnet {
 
 
     uint8_t *rxmem;
+    uint32_t *rxapp;
+    uint32_t rxsize;
+    uint32_t rxpos;
 };
 
 static void axienet_rx_reset(XilinxAXIEnet *s)
@@ -645,7 +648,7 @@ static int eth_can_rx(NetClientState *nc)
     XilinxAXIEnet *s = qemu_get_nic_opaque(nc);
 
     /* RX enabled?  */
-    return !axienet_rx_resetting(s) && axienet_rx_enabled(s);
+    return !s->rxsize && !axienet_rx_resetting(s) && axienet_rx_enabled(s);
 }
 
 static int enet_match_addr(const uint8_t *buf, uint32_t f0, uint32_t f1)
@@ -663,6 +666,23 @@ static int enet_match_addr(const uint8_t *buf, uint32_t f0, uint32_t f1)
     return match;
 }
 
+static void axienet_eth_rx_notify(void *opaque)
+{
+    XilinxAXIEnet *s = XILINX_AXI_ENET(opaque);
+
+    while (s->rxsize && stream_can_push(s->tx_dev, axienet_eth_rx_notify, s)) {
+        size_t ret = stream_push(s->tx_dev, (void *)s->rxmem + s->rxpos,
+                                 s->rxsize, s->rxapp);
+        s->rxsize -= ret;
+        s->rxpos += ret;
+        if (!s->rxsize) {
+            s->regs[R_IS] |= IS_RX_COMPLETE;
+            g_free(s->rxapp);
+        }
+    }
+    enet_update_irq(s);
+}
+
 static ssize_t eth_rx(NetClientState *nc, const uint8_t *buf, size_t size)
 {
     XilinxAXIEnet *s = qemu_get_nic_opaque(nc);
@@ -800,9 +820,11 @@ static ssize_t eth_rx(NetClientState *nc, const uint8_t *buf, size_t size)
     /* Good frame.  */
     app[2] |= 1 << 6;
 
-    stream_push(s->tx_dev, (void *)s->rxmem, size, app);
+    s->rxsize = size;
+    s->rxpos = 0;
+    s->rxapp = g_memdup(app, sizeof(app));
+    axienet_eth_rx_notify(s);
 
-    s->regs[R_IS] |= IS_RX_COMPLETE;
     enet_update_irq(s);
     return size;
 }