[PATCH] net/imx_fec: Updating the IMX_FEC IP to support loopback mode.

[bilalwasim676@gmail.com]

From: bwasim <bilal_wasim@mentor.com>

Loopback mode only works when specific conditions (as dictated
by the IP guide) are met, i.e. the MII_MODE is set and the
RMII_MODE is cleared. If not, we simply send the packet on the
output queue (for TX to the host network). Tested by running a
custom RTOS and TXing a ton of packets. The same packets were
received on the RX side..

Signed-off-by: Bilal Wasim <bilal_wasim@mentor.com>
---
 hw/net/imx_fec.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c
index bd99236864..c51e7f7363 100644
--- a/hw/net/imx_fec.c
+++ b/hw/net/imx_fec.c
@@ -256,6 +256,29 @@ static const VMStateDescription vmstate_imx_eth = {
 
 static void imx_eth_update(IMXFECState *s);
 
+/*
+ * Function to check if the MAC is configured to run in loopback mode.
+ * If so, invoke the "receive" routine.
+ * Else write to the output.
+ * */
+static void send_pkt(IMXFECState *s, uint8_t *frame, int frame_size)
+{
+    NetClientState *nc = qemu_get_queue(s->nic);
+
+    /*
+     * Loopback or Normal mode ?
+     * Per the FEC Manual: If loopback is enabled, the MII_MODE
+     * should be SET and the RMII_MODE should be cleared. Loopback
+     * will only work if this criterion is met. If not met,
+     * we will send the frame on the output queue. */
+    if ((s->regs[ENET_RCR] & ENET_RCR_LOOP) && (s->regs[ENET_RCR] & ENET_RCR_MII_MODE)
+            && !(s->regs[ENET_RCR] & ENET_RCR_RMII_MODE)) {
+        nc->info->receive(nc, frame, frame_size);
+    } else {
+        qemu_send_packet(nc, frame, frame_size);
+    }
+}
+
 /*
  * The MII phy could raise a GPIO to the processor which in turn
  * could be handled as an interrpt by the OS.
@@ -488,7 +511,7 @@ static void imx_fec_do_tx(IMXFECState *s)
         frame_size += len;
         if (bd.flags & ENET_BD_L) {
             /* Last buffer in frame.  */
-            qemu_send_packet(qemu_get_queue(s->nic), s->frame, frame_size);
+            send_pkt(s, (uint8_t *)&s->frame, frame_size);
             ptr = s->frame;
             frame_size = 0;
             s->regs[ENET_EIR] |= ENET_INT_TXF;
@@ -586,7 +609,7 @@ static void imx_enet_do_tx(IMXFECState *s, uint32_t index)
             }
             /* Last buffer in frame.  */
 
-            qemu_send_packet(qemu_get_queue(s->nic), s->frame, frame_size);
+            send_pkt(s, (uint8_t *)&s->frame, frame_size);
             ptr = s->frame;
 
             frame_size = 0;
-- 
2.19.1.windows.1