[Qemu-devel] [PATCH] hw/net: handle flow control in mcf_fec driver receiver

[Greg Ungerer]

The network mcf_fec driver emulated receive side method is not dealing
with network queue flow control properly.

Modify the receive side to check if we have enough space in the
descriptors to store the current packet. If not we process none of it
and return 0. When the guest frees up some buffers through its descriptors
we signal the qemu net layer to send more packets.

Signed-off-by: Greg Ungerer <address@hidden>
---
 hw/net/mcf_fec.c | 45 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/hw/net/mcf_fec.c b/hw/net/mcf_fec.c
index e63af1b..1775e76 100644
--- a/hw/net/mcf_fec.c
+++ b/hw/net/mcf_fec.c
@@ -196,12 +196,14 @@ static void mcf_fec_do_tx(mcf_fec_state *s)
 
 static void mcf_fec_enable_rx(mcf_fec_state *s)
 {
+    NetClientState *nc = qemu_get_queue(s->nic);
     mcf_fec_bd bd;
 
     mcf_fec_read_bd(&bd, s->rx_descriptor);
     s->rx_enabled = ((bd.flags & FEC_BD_E) != 0);
-    if (!s->rx_enabled)
-        DPRINTF("RX buffer full\n");
+    if (s->rx_enabled) {
+        qemu_flush_queued_packets(nc);
+    }
 }
 
 static void mcf_fec_reset(mcf_fec_state *s)
@@ -403,6 +405,31 @@ static int mcf_fec_can_receive(NetClientState *nc)
     return s->rx_enabled;
 }
 
+static int mcf_fec_have_receive_space(mcf_fec_state *s, size_t want)
+{
+    mcf_fec_bd bd;
+    uint32_t addr;
+
+    /* Walk descriptor list to determine if we have enough buffer */
+    addr = s->rx_descriptor;
+    while (want > 0) {
+        mcf_fec_read_bd(&bd, addr);
+        if ((bd.flags & FEC_BD_E) == 0) {
+            return 0;
+        }
+        if (want < s->emrbr)
+            return 1;
+       want -= s->emrbr;
+        /* Advance to the next descriptor.  */
+        if ((bd.flags & FEC_BD_W) != 0) {
+            addr = s->erdsr;
+        } else {
+            addr += 8;
+        }
+    }
+    return 0;
+}
+
 static ssize_t mcf_fec_receive(NetClientState *nc, const uint8_t *buf, size_t 
size)
 {
     mcf_fec_state *s = qemu_get_nic_opaque(nc);
@@ -417,7 +444,7 @@ static ssize_t mcf_fec_receive(NetClientState *nc, const 
uint8_t *buf, size_t si
 
     DPRINTF("do_rx len %d\n", size);
     if (!s->rx_enabled) {
-        fprintf(stderr, "mcf_fec_receive: Unexpected packet\n");
+        return -1;
     }
     /* 4 bytes for the CRC.  */
     size += 4;
@@ -432,18 +459,14 @@ static ssize_t mcf_fec_receive(NetClientState *nc, const 
uint8_t *buf, size_t si
     if (size > (s->rcr >> 16)) {
         flags |= FEC_BD_LG;
     }
+    /* Check if we have enough space in current descriptors */
+    if (!mcf_fec_have_receive_space(s, size)) {
+        return 0;
+    }
     addr = s->rx_descriptor;
     retsize = size;
     while (size > 0) {
         mcf_fec_read_bd(&bd, addr);
-        if ((bd.flags & FEC_BD_E) == 0) {
-            /* No descriptors available.  Bail out.  */
-            /* FIXME: This is wrong.  We should probably either save the
-               remainder for when more RX buffers are available, or
-               flag an error.  */
-            fprintf(stderr, "mcf_fec: Lost end of frame\n");
-            break;
-        }
         buf_len = (size <= s->emrbr) ? size: s->emrbr;
         bd.length = buf_len;
         size -= buf_len;
-- 
1.9.1