net: zynq: Add dummy packet to fix packet duplication issue

Target is duplicating packets. IP prefetches another BD and process it
when the first one is sent. Adding one dummy BD to the chain fix the
problem with packet duplication.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

drivers/net/zynq_gem.c

@@ -46,6 +46,7 @@
 /* Wrap bit, last descriptor */
 #define ZYNQ_GEM_TXBUF_WRAP_MASK	0x40000000
 #define ZYNQ_GEM_TXBUF_LAST_MASK	0x00008000 /* Last buffer */
+#define ZYNQ_GEM_TXBUF_USED_MASK	0x80000000 /* Used by Hw */
 
 #define ZYNQ_GEM_NWCTRL_TXEN_MASK	0x00000008 /* Enable transmit */
 #define ZYNQ_GEM_NWCTRL_RXEN_MASK	0x00000004 /* Enable receive */
@@ -405,14 +406,19 @@ static int zynq_gem_send(struct eth_device *dev, void *ptr, int len)
 	u32 addr, size;
 	struct zynq_gem_priv *priv = dev->priv;
 	struct zynq_gem_regs *regs = (struct zynq_gem_regs *)dev->iobase;
+	struct emac_bd *current_bd = &priv->tx_bd[1];
 
 	/* Setup Tx BD */
 	memset(priv->tx_bd, 0, sizeof(struct emac_bd));
 
 	priv->tx_bd->addr = (ulong)ptr;
 	priv->tx_bd->status = (len & ZYNQ_GEM_TXBUF_FRMLEN_MASK) |
-			       ZYNQ_GEM_TXBUF_LAST_MASK |
-			       ZYNQ_GEM_TXBUF_WRAP_MASK;
+			       ZYNQ_GEM_TXBUF_LAST_MASK;
+	/* Dummy descriptor to mark it as the last in descriptor chain */
+	current_bd->addr = 0x0;
+	current_bd->status = ZYNQ_GEM_TXBUF_WRAP_MASK |
+			     ZYNQ_GEM_TXBUF_LAST_MASK|
+			     ZYNQ_GEM_TXBUF_USED_MASK;
 
 	/* setup BD */
 	writel((ulong)priv->tx_bd, &regs->txqbase);