net: fec: fix the error to get the previous BD entry

Bug: error to get the previous BD entry. When the current BD
is the first BD, the previous BD entry must be the last BD,
not "bdp - 1" in current logic.

V4:
  * Optimize fec_enet_get_nextdesc() for code clean.
    Replace "ex_new_bd - ring_size" with "ex_base".
    Replace "new_bd - ring_size" with "base".

V3:
  * Restore the API name because David suggest to use fec_enet_
    prefix for all function in fec driver.
    So, change next_bd() -> fec_enet_get_nextdesc()
        change pre_bd()  -> fec_enet_get_prevdesc()
  * Reduce the two APIs parameters for easy to call.

V2:
  * Add tx_ring_size and rx_ring_size to struct fec_enet_private.
  * Replace api fec_enet_get_nextdesc() with next_bd().
    Replace api fec_enet_get_prevdesc() with pre_bd().

  * Move all ring size check logic to next_bd() and pre_bd(), which
    simplifies the code redundancy.

V1:
  * Add BD ring size check to get the previous BD entry in correctly.
Reviewed-by: NLi Frank <B20596@freescale.com>
Signed-off-by: NFugang Duan  <B38611@freescale.com>
Acked-by: NFrank Li <frank.li@freescale.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec.h

@@ -296,6 +296,9 @@ struct fec_enet_private {
 	/* The ring entries to be free()ed */
 	struct bufdesc	*dirty_tx;
 
+	unsigned short tx_ring_size;
+	unsigned short rx_ring_size;
+
 	struct	platform_device *pdev;
 
 	int	opened;

drivers/net/ethernet/freescale/fec_main.c

@@ -239,22 +239,57 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet MAC address");
 
 static int mii_cnt;
 
-static struct bufdesc *fec_enet_get_nextdesc(struct bufdesc *bdp, int is_ex)
+static inline
+struct bufdesc *fec_enet_get_nextdesc(struct bufdesc *bdp, struct fec_enet_private *fep)
 {
-	struct bufdesc_ex *ex = (struct bufdesc_ex *)bdp;
-	if (is_ex)
-		return (struct bufdesc *)(ex + 1);
+	struct bufdesc *new_bd = bdp + 1;
+	struct bufdesc_ex *ex_new_bd = (struct bufdesc_ex *)bdp + 1;
+	struct bufdesc_ex *ex_base;
+	struct bufdesc *base;
+	int ring_size;
+
+	if (bdp >= fep->tx_bd_base) {
+		base = fep->tx_bd_base;
+		ring_size = fep->tx_ring_size;
+		ex_base = (struct bufdesc_ex *)fep->tx_bd_base;
+	} else {
+		base = fep->rx_bd_base;
+		ring_size = fep->rx_ring_size;
+		ex_base = (struct bufdesc_ex *)fep->rx_bd_base;
+	}
+
+	if (fep->bufdesc_ex)
+		return (struct bufdesc *)((ex_new_bd >= (ex_base + ring_size)) ?
+			ex_base : ex_new_bd);
 	else
-		return bdp + 1;
+		return (new_bd >= (base + ring_size)) ?
+			base : new_bd;
 }
 
-static struct bufdesc *fec_enet_get_prevdesc(struct bufdesc *bdp, int is_ex)
+static inline
+struct bufdesc *fec_enet_get_prevdesc(struct bufdesc *bdp, struct fec_enet_private *fep)
 {
-	struct bufdesc_ex *ex = (struct bufdesc_ex *)bdp;
-	if (is_ex)
-		return (struct bufdesc *)(ex - 1);
+	struct bufdesc *new_bd = bdp - 1;
+	struct bufdesc_ex *ex_new_bd = (struct bufdesc_ex *)bdp - 1;
+	struct bufdesc_ex *ex_base;
+	struct bufdesc *base;
+	int ring_size;
+
+	if (bdp >= fep->tx_bd_base) {
+		base = fep->tx_bd_base;
+		ring_size = fep->tx_ring_size;
+		ex_base = (struct bufdesc_ex *)fep->tx_bd_base;
+	} else {
+		base = fep->rx_bd_base;
+		ring_size = fep->rx_ring_size;
+		ex_base = (struct bufdesc_ex *)fep->rx_bd_base;
+	}
+
+	if (fep->bufdesc_ex)
+		return (struct bufdesc *)((ex_new_bd < ex_base) ?
+			(ex_new_bd + ring_size) : ex_new_bd);
 	else
-		return bdp - 1;
+		return (new_bd < base) ? (new_bd + ring_size) : new_bd;
 }
 
 static void *swap_buffer(void *bufaddr, int len)
@@ -380,7 +415,7 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		}
 	}
 
-	bdp_pre = fec_enet_get_prevdesc(bdp, fep->bufdesc_ex);
+	bdp_pre = fec_enet_get_prevdesc(bdp, fep);
 	if ((id_entry->driver_data & FEC_QUIRK_ERR006358) &&
 	    !(bdp_pre->cbd_sc & BD_ENET_TX_READY)) {
 		fep->delay_work.trig_tx = true;
@@ -389,10 +424,7 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	}
 
 	/* If this was the last BD in the ring, start at the beginning again. */
-	if (status & BD_ENET_TX_WRAP)
-		bdp = fep->tx_bd_base;
-	else
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_nextdesc(bdp, fep);
 
 	fep->cur_tx = bdp;
 
@@ -417,18 +449,18 @@ static void fec_enet_bd_init(struct net_device *dev)
 
 	/* Initialize the receive buffer descriptors. */
 	bdp = fep->rx_bd_base;
-	for (i = 0; i < RX_RING_SIZE; i++) {
+	for (i = 0; i < fep->rx_ring_size; i++) {
 
 		/* Initialize the BD for every fragment in the page. */
 		if (bdp->cbd_bufaddr)
 			bdp->cbd_sc = BD_ENET_RX_EMPTY;
 		else
 			bdp->cbd_sc = 0;
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 	}
 
 	/* Set the last buffer to wrap */
-	bdp = fec_enet_get_prevdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_prevdesc(bdp, fep);
 	bdp->cbd_sc |= BD_SC_WRAP;
 
 	fep->cur_rx = fep->rx_bd_base;
@@ -436,7 +468,7 @@ static void fec_enet_bd_init(struct net_device *dev)
 	/* ...and the same for transmit */
 	bdp = fep->tx_bd_base;
 	fep->cur_tx = bdp;
-	for (i = 0; i < TX_RING_SIZE; i++) {
+	for (i = 0; i < fep->tx_ring_size; i++) {
 
 		/* Initialize the BD for every fragment in the page. */
 		bdp->cbd_sc = 0;
@@ -445,11 +477,11 @@ static void fec_enet_bd_init(struct net_device *dev)
 			fep->tx_skbuff[i] = NULL;
 		}
 		bdp->cbd_bufaddr = 0;
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 	}
 
 	/* Set the last buffer to wrap */
-	bdp = fec_enet_get_prevdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_prevdesc(bdp, fep);
 	bdp->cbd_sc |= BD_SC_WRAP;
 	fep->dirty_tx = bdp;
 }
@@ -510,10 +542,10 @@ fec_restart(struct net_device *ndev, int duplex)
 	writel(fep->bd_dma, fep->hwp + FEC_R_DES_START);
 	if (fep->bufdesc_ex)
 		writel((unsigned long)fep->bd_dma + sizeof(struct bufdesc_ex)
-			* RX_RING_SIZE, fep->hwp + FEC_X_DES_START);
+			* fep->rx_ring_size, fep->hwp + FEC_X_DES_START);
 	else
 		writel((unsigned long)fep->bd_dma + sizeof(struct bufdesc)
-			* RX_RING_SIZE,	fep->hwp + FEC_X_DES_START);
+			* fep->rx_ring_size,	fep->hwp + FEC_X_DES_START);
 
 
 	for (i = 0; i <= TX_RING_MOD_MASK; i++) {
@@ -727,10 +759,7 @@ fec_enet_tx(struct net_device *ndev)
 	bdp = fep->dirty_tx;
 
 	/* get next bdp of dirty_tx */
-	if (bdp->cbd_sc & BD_ENET_TX_WRAP)
-		bdp = fep->tx_bd_base;
-	else
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_nextdesc(bdp, fep);
 
 	while (((status = bdp->cbd_sc) & BD_ENET_TX_READY) == 0) {
 
@@ -800,10 +829,7 @@ fec_enet_tx(struct net_device *ndev)
 		fep->dirty_tx = bdp;
 
 		/* Update pointer to next buffer descriptor to be transmitted */
-		if (status & BD_ENET_TX_WRAP)
-			bdp = fep->tx_bd_base;
-		else
-			bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 
 		/* Since we have freed up a buffer, the ring is no longer full
 		 */
@@ -993,10 +1019,8 @@ fec_enet_rx(struct net_device *ndev, int budget)
 		}
 
 		/* Update BD pointer to next entry */
-		if (status & BD_ENET_RX_WRAP)
-			bdp = fep->rx_bd_base;
-		else
-			bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
+
 		/* Doing this here will keep the FEC running while we process
 		 * incoming frames.  On a heavily loaded network, we should be
 		 * able to keep up at the expense of system resources.
@@ -1662,7 +1686,7 @@ static void fec_enet_free_buffers(struct net_device *ndev)
 	struct bufdesc	*bdp;
 
 	bdp = fep->rx_bd_base;
-	for (i = 0; i < RX_RING_SIZE; i++) {
+	for (i = 0; i < fep->rx_ring_size; i++) {
 		skb = fep->rx_skbuff[i];
 
 		if (bdp->cbd_bufaddr)
@@ -1670,11 +1694,11 @@ static void fec_enet_free_buffers(struct net_device *ndev)
 					FEC_ENET_RX_FRSIZE, DMA_FROM_DEVICE);
 		if (skb)
 			dev_kfree_skb(skb);
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 	}
 
 	bdp = fep->tx_bd_base;
-	for (i = 0; i < TX_RING_SIZE; i++)
+	for (i = 0; i < fep->tx_ring_size; i++)
 		kfree(fep->tx_bounce[i]);
 }
 
@@ -1686,7 +1710,7 @@ static int fec_enet_alloc_buffers(struct net_device *ndev)
 	struct bufdesc	*bdp;
 
 	bdp = fep->rx_bd_base;
-	for (i = 0; i < RX_RING_SIZE; i++) {
+	for (i = 0; i < fep->rx_ring_size; i++) {
 		skb = netdev_alloc_skb(ndev, FEC_ENET_RX_FRSIZE);
 		if (!skb) {
 			fec_enet_free_buffers(ndev);
@@ -1703,15 +1727,15 @@ static int fec_enet_alloc_buffers(struct net_device *ndev)
 			ebdp->cbd_esc = BD_ENET_RX_INT;
 		}
 
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 	}
 
 	/* Set the last buffer to wrap. */
-	bdp = fec_enet_get_prevdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_prevdesc(bdp, fep);
 	bdp->cbd_sc |= BD_SC_WRAP;
 
 	bdp = fep->tx_bd_base;
-	for (i = 0; i < TX_RING_SIZE; i++) {
+	for (i = 0; i < fep->tx_ring_size; i++) {
 		fep->tx_bounce[i] = kmalloc(FEC_ENET_TX_FRSIZE, GFP_KERNEL);
 
 		bdp->cbd_sc = 0;
@@ -1722,11 +1746,11 @@ static int fec_enet_alloc_buffers(struct net_device *ndev)
 			ebdp->cbd_esc = BD_ENET_TX_INT;
 		}
 
-		bdp = fec_enet_get_nextdesc(bdp, fep->bufdesc_ex);
+		bdp = fec_enet_get_nextdesc(bdp, fep);
 	}
 
 	/* Set the last buffer to wrap. */
-	bdp = fec_enet_get_prevdesc(bdp, fep->bufdesc_ex);
+	bdp = fec_enet_get_prevdesc(bdp, fep);
 	bdp->cbd_sc |= BD_SC_WRAP;
 
 	return 0;
@@ -1966,13 +1990,17 @@ static int fec_enet_init(struct net_device *ndev)
 	/* Get the Ethernet address */
 	fec_get_mac(ndev);
 
+	/* init the tx & rx ring size */
+	fep->tx_ring_size = TX_RING_SIZE;
+	fep->rx_ring_size = RX_RING_SIZE;
+
 	/* Set receive and transmit descriptor base. */
 	fep->rx_bd_base = cbd_base;
 	if (fep->bufdesc_ex)
 		fep->tx_bd_base = (struct bufdesc *)
-			(((struct bufdesc_ex *)cbd_base) + RX_RING_SIZE);
+			(((struct bufdesc_ex *)cbd_base) + fep->rx_ring_size);
 	else
-		fep->tx_bd_base = cbd_base + RX_RING_SIZE;
+		fep->tx_bd_base = cbd_base + fep->rx_ring_size;
 
 	/* The FEC Ethernet specific entries in the device structure */
 	ndev->watchdog_timeo = TX_TIMEOUT;