net/macb: clean up ring buffer logic

Instead of masking head and tail every time we increment them, just let them
wrap through UINT_MAX and mask them when subscripting. Add simple accessor
functions to do the subscripting properly to minimize the chances of messing
this up.

This makes the code slightly smaller, and hopefully faster as well.  Also,
doing the ring buffer management this way will simplify things a lot when
making the ring sizes configurable in the future.

Available number of descriptors in ring buffer function by David Laight.

Signed-off-by: Havard Skinnemoen <havard@skinnemoen.net>
[nicolas.ferre@atmel.com: split patch in topics, adapt to newer kernel]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/at91_ether.c

@@ -156,7 +156,7 @@ static int at91ether_start(struct net_device *dev)
 	int i;
 
 	lp->rx_ring = dma_alloc_coherent(&lp->pdev->dev,
-					MAX_RX_DESCR * sizeof(struct dma_desc),
+					MAX_RX_DESCR * sizeof(struct macb_dma_desc),
 					&lp->rx_ring_dma, GFP_KERNEL);
 	if (!lp->rx_ring) {
 		netdev_err(lp->dev, "unable to alloc rx ring DMA buffer\n");
@@ -170,7 +170,7 @@ static int at91ether_start(struct net_device *dev)
 		netdev_err(lp->dev, "unable to alloc rx data DMA buffer\n");
 
 		dma_free_coherent(&lp->pdev->dev,
-					MAX_RX_DESCR * sizeof(struct dma_desc),
+					MAX_RX_DESCR * sizeof(struct macb_dma_desc),
 					lp->rx_ring, lp->rx_ring_dma);
 		lp->rx_ring = NULL;
 		return -ENOMEM;
@@ -256,7 +256,7 @@ static int at91ether_close(struct net_device *dev)
 	netif_stop_queue(dev);
 
 	dma_free_coherent(&lp->pdev->dev,
-				MAX_RX_DESCR * sizeof(struct dma_desc),
+				MAX_RX_DESCR * sizeof(struct macb_dma_desc),
 				lp->rx_ring, lp->rx_ring_dma);
 	lp->rx_ring = NULL;
 

drivers/net/ethernet/cadence/macb.c

@@ -30,25 +30,14 @@
 #include "macb.h"
 
 #define RX_BUFFER_SIZE		128
-#define RX_RING_SIZE		512
-#define RX_RING_BYTES		(sizeof(struct dma_desc) * RX_RING_SIZE)
+#define RX_RING_SIZE		512 /* must be power of 2 */
+#define RX_RING_BYTES		(sizeof(struct macb_dma_desc) * RX_RING_SIZE)
 
 /* Make the IP header word-aligned (the ethernet header is 14 bytes) */
 #define RX_OFFSET		2
 
-#define TX_RING_SIZE		128
-#define DEF_TX_RING_PENDING	(TX_RING_SIZE - 1)
-#define TX_RING_BYTES		(sizeof(struct dma_desc) * TX_RING_SIZE)
-
-#define TX_RING_GAP(bp)						\
-	(TX_RING_SIZE - (bp)->tx_pending)
-#define TX_BUFFS_AVAIL(bp)					\
-	(((bp)->tx_tail <= (bp)->tx_head) ?			\
-	 (bp)->tx_tail + (bp)->tx_pending - (bp)->tx_head :	\
-	 (bp)->tx_tail - (bp)->tx_head - TX_RING_GAP(bp))
-#define NEXT_TX(n)		(((n) + 1) & (TX_RING_SIZE - 1))
-
-#define NEXT_RX(n)		(((n) + 1) & (RX_RING_SIZE - 1))
+#define TX_RING_SIZE		128 /* must be power of 2 */
+#define TX_RING_BYTES		(sizeof(struct macb_dma_desc) * TX_RING_SIZE)
 
 /* minimum number of free TX descriptors before waking up TX process */
 #define MACB_TX_WAKEUP_THRESH	(TX_RING_SIZE / 4)
@@ -56,6 +45,51 @@
 #define MACB_RX_INT_FLAGS	(MACB_BIT(RCOMP) | MACB_BIT(RXUBR)	\
 				 | MACB_BIT(ISR_ROVR))
 
+/* Ring buffer accessors */
+static unsigned int macb_tx_ring_wrap(unsigned int index)
+{
+	return index & (TX_RING_SIZE - 1);
+}
+
+static unsigned int macb_tx_ring_avail(struct macb *bp)
+{
+	return (bp->tx_tail - bp->tx_head) & (TX_RING_SIZE - 1);
+}
+
+static struct macb_dma_desc *macb_tx_desc(struct macb *bp, unsigned int index)
+{
+	return &bp->tx_ring[macb_tx_ring_wrap(index)];
+}
+
+static struct macb_tx_skb *macb_tx_skb(struct macb *bp, unsigned int index)
+{
+	return &bp->tx_skb[macb_tx_ring_wrap(index)];
+}
+
+static dma_addr_t macb_tx_dma(struct macb *bp, unsigned int index)
+{
+	dma_addr_t offset;
+
+	offset = macb_tx_ring_wrap(index) * sizeof(struct macb_dma_desc);
+
+	return bp->tx_ring_dma + offset;
+}
+
+static unsigned int macb_rx_ring_wrap(unsigned int index)
+{
+	return index & (RX_RING_SIZE - 1);
+}
+
+static struct macb_dma_desc *macb_rx_desc(struct macb *bp, unsigned int index)
+{
+	return &bp->rx_ring[macb_rx_ring_wrap(index)];
+}
+
+static void *macb_rx_buffer(struct macb *bp, unsigned int index)
+{
+	return bp->rx_buffers + RX_BUFFER_SIZE * macb_rx_ring_wrap(index);
+}
+
 static void __macb_set_hwaddr(struct macb *bp)
 {
 	u32 bottom;
@@ -336,17 +370,18 @@ static void macb_tx(struct macb *bp)
 		bp->tx_ring[TX_RING_SIZE - 1].ctrl |= MACB_BIT(TX_WRAP);
 
 		/* free transmit buffer in upper layer*/
-		for (tail = bp->tx_tail; tail != head; tail = NEXT_TX(tail)) {
-			struct ring_info *rp = &bp->tx_skb[tail];
-			struct sk_buff *skb = rp->skb;
-
-			BUG_ON(skb == NULL);
+		for (tail = bp->tx_tail; tail != head; tail++) {
+			struct macb_tx_skb	*tx_skb;
+			struct sk_buff		*skb;
 
 			rmb();
 
-			dma_unmap_single(&bp->pdev->dev, rp->mapping, skb->len,
-							 DMA_TO_DEVICE);
-			rp->skb = NULL;
+			tx_skb = macb_tx_skb(bp, tail);
+			skb = tx_skb->skb;
+
+			dma_unmap_single(&bp->pdev->dev, tx_skb->mapping,
+						skb->len, DMA_TO_DEVICE);
+			tx_skb->skb = NULL;
 			dev_kfree_skb_irq(skb);
 		}
 
@@ -366,34 +401,38 @@ static void macb_tx(struct macb *bp)
 		return;
 
 	head = bp->tx_head;
-	for (tail = bp->tx_tail; tail != head; tail = NEXT_TX(tail)) {
-		struct ring_info *rp = &bp->tx_skb[tail];
-		struct sk_buff *skb = rp->skb;
-		u32 bufstat;
+	for (tail = bp->tx_tail; tail != head; tail++) {
+		struct macb_tx_skb	*tx_skb;
+		struct sk_buff		*skb;
+		struct macb_dma_desc	*desc;
+		u32			ctrl;
 
-		BUG_ON(skb == NULL);
+		desc = macb_tx_desc(bp, tail);
 
 		/* Make hw descriptor updates visible to CPU */
 		rmb();
 
-		bufstat = bp->tx_ring[tail].ctrl;
+		ctrl = desc->ctrl;
 
-		if (!(bufstat & MACB_BIT(TX_USED)))
+		if (!(ctrl & MACB_BIT(TX_USED)))
 			break;
 
+		tx_skb = macb_tx_skb(bp, tail);
+		skb = tx_skb->skb;
+
 		netdev_vdbg(bp->dev, "skb %u (data %p) TX complete\n",
-			   tail, skb->data);
-		dma_unmap_single(&bp->pdev->dev, rp->mapping, skb->len,
+			macb_tx_ring_wrap(tail), skb->data);
+		dma_unmap_single(&bp->pdev->dev, tx_skb->mapping, skb->len,
 				 DMA_TO_DEVICE);
 		bp->stats.tx_packets++;
 		bp->stats.tx_bytes += skb->len;
-		rp->skb = NULL;
+		tx_skb->skb = NULL;
 		dev_kfree_skb_irq(skb);
 	}
 
 	bp->tx_tail = tail;
-	if (netif_queue_stopped(bp->dev) &&
-	    TX_BUFFS_AVAIL(bp) > MACB_TX_WAKEUP_THRESH)
+	if (netif_queue_stopped(bp->dev)
+			&& macb_tx_ring_avail(bp) > MACB_TX_WAKEUP_THRESH)
 		netif_wake_queue(bp->dev);
 }
 
@@ -404,17 +443,21 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
 	unsigned int frag;
 	unsigned int offset = 0;
 	struct sk_buff *skb;
+	struct macb_dma_desc *desc;
 
-	len = MACB_BFEXT(RX_FRMLEN, bp->rx_ring[last_frag].ctrl);
+	desc = macb_rx_desc(bp, last_frag);
+	len = MACB_BFEXT(RX_FRMLEN, desc->ctrl);
 
 	netdev_vdbg(bp->dev, "macb_rx_frame frags %u - %u (len %u)\n",
-		   first_frag, last_frag, len);
+		macb_rx_ring_wrap(first_frag),
+		macb_rx_ring_wrap(last_frag), len);
 
 	skb = netdev_alloc_skb(bp->dev, len + RX_OFFSET);
 	if (!skb) {
 		bp->stats.rx_dropped++;
-		for (frag = first_frag; ; frag = NEXT_RX(frag)) {
-			bp->rx_ring[frag].addr &= ~MACB_BIT(RX_USED);
+		for (frag = first_frag; ; frag++) {
+			desc = macb_rx_desc(bp, frag);
+			desc->addr &= ~MACB_BIT(RX_USED);
 			if (frag == last_frag)
 				break;
 		}
@@ -429,7 +472,7 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
 	skb_checksum_none_assert(skb);
 	skb_put(skb, len);
 
-	for (frag = first_frag; ; frag = NEXT_RX(frag)) {
+	for (frag = first_frag; ; frag++) {
 		unsigned int frag_len = RX_BUFFER_SIZE;
 
 		if (offset + frag_len > len) {
@@ -437,11 +480,10 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
 			frag_len = len - offset;
 		}
 		skb_copy_to_linear_data_offset(skb, offset,
-					       (bp->rx_buffers +
-					        (RX_BUFFER_SIZE * frag)),
-					       frag_len);
+				macb_rx_buffer(bp, frag), frag_len);
 		offset += RX_BUFFER_SIZE;
-		bp->rx_ring[frag].addr &= ~MACB_BIT(RX_USED);
+		desc = macb_rx_desc(bp, frag);
+		desc->addr &= ~MACB_BIT(RX_USED);
 
 		if (frag == last_frag)
 			break;
@@ -467,8 +509,10 @@ static void discard_partial_frame(struct macb *bp, unsigned int begin,
 {
 	unsigned int frag;
 
-	for (frag = begin; frag != end; frag = NEXT_RX(frag))
-		bp->rx_ring[frag].addr &= ~MACB_BIT(RX_USED);
+	for (frag = begin; frag != end; frag++) {
+		struct macb_dma_desc *desc = macb_rx_desc(bp, frag);
+		desc->addr &= ~MACB_BIT(RX_USED);
+	}
 
 	/* Make descriptor updates visible to hardware */
 	wmb();
@@ -483,17 +527,18 @@ static void discard_partial_frame(struct macb *bp, unsigned int begin,
 static int macb_rx(struct macb *bp, int budget)
 {
 	int received = 0;
-	unsigned int tail = bp->rx_tail;
+	unsigned int tail;
 	int first_frag = -1;
 
-	for (; budget > 0; tail = NEXT_RX(tail)) {
+	for (tail = bp->rx_tail; budget > 0; tail++) {
+		struct macb_dma_desc *desc = macb_rx_desc(bp, tail);
 		u32 addr, ctrl;
 
 		/* Make hw descriptor updates visible to CPU */
 		rmb();
 
-		addr = bp->rx_ring[tail].addr;
-		ctrl = bp->rx_ring[tail].ctrl;
+		addr = desc->addr;
+		ctrl = desc->ctrl;
 
 		if (!(addr & MACB_BIT(RX_USED)))
 			break;
@@ -647,6 +692,8 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct macb *bp = netdev_priv(dev);
 	dma_addr_t mapping;
 	unsigned int len, entry;
+	struct macb_dma_desc *desc;
+	struct macb_tx_skb *tx_skb;
 	u32 ctrl;
 	unsigned long flags;
 
@@ -663,7 +710,7 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	spin_lock_irqsave(&bp->lock, flags);
 
 	/* This is a hard error, log it. */
-	if (TX_BUFFS_AVAIL(bp) < 1) {
+	if (macb_tx_ring_avail(bp) < 1) {
 		netif_stop_queue(dev);
 		spin_unlock_irqrestore(&bp->lock, flags);
 		netdev_err(bp->dev, "BUG! Tx Ring full when queue awake!\n");
@@ -672,12 +719,15 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		return NETDEV_TX_BUSY;
 	}
 
-	entry = bp->tx_head;
+	entry = macb_tx_ring_wrap(bp->tx_head);
+	bp->tx_head++;
 	netdev_vdbg(bp->dev, "Allocated ring entry %u\n", entry);
 	mapping = dma_map_single(&bp->pdev->dev, skb->data,
 				 len, DMA_TO_DEVICE);
-	bp->tx_skb[entry].skb = skb;
-	bp->tx_skb[entry].mapping = mapping;
+
+	tx_skb = &bp->tx_skb[entry];
+	tx_skb->skb = skb;
+	tx_skb->mapping = mapping;
 	netdev_vdbg(bp->dev, "Mapped skb data %p to DMA addr %08lx\n",
 		   skb->data, (unsigned long)mapping);
 
@@ -686,20 +736,18 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (entry == (TX_RING_SIZE - 1))
 		ctrl |= MACB_BIT(TX_WRAP);
 
-	bp->tx_ring[entry].addr = mapping;
-	bp->tx_ring[entry].ctrl = ctrl;
+	desc = &bp->tx_ring[entry];
+	desc->addr = mapping;
+	desc->ctrl = ctrl;
 
 	/* Make newly initialized descriptor visible to hardware */
 	wmb();
 
-	entry = NEXT_TX(entry);
-	bp->tx_head = entry;
-
 	skb_tx_timestamp(skb);
 
 	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
 
-	if (TX_BUFFS_AVAIL(bp) < 1)
+	if (macb_tx_ring_avail(bp) < 1)
 		netif_stop_queue(dev);
 
 	spin_unlock_irqrestore(&bp->lock, flags);
@@ -735,7 +783,7 @@ static int macb_alloc_consistent(struct macb *bp)
 {
 	int size;
 
-	size = TX_RING_SIZE * sizeof(struct ring_info);
+	size = TX_RING_SIZE * sizeof(struct macb_tx_skb);
 	bp->tx_skb = kmalloc(size, GFP_KERNEL);
 	if (!bp->tx_skb)
 		goto out_err;
@@ -1412,8 +1460,6 @@ static int __init macb_probe(struct platform_device *pdev)
 		macb_or_gem_writel(bp, USRIO, MACB_BIT(MII));
 #endif
 
-	bp->tx_pending = DEF_TX_RING_PENDING;
-
 	err = register_netdev(dev);
 	if (err) {
 		dev_err(&pdev->dev, "Cannot register net device, aborting.\n");

drivers/net/ethernet/cadence/macb.h

@@ -362,7 +362,12 @@
 		__v; \
 	})
 
-struct dma_desc {
+/**
+ * struct macb_dma_desc - Hardware DMA descriptor
+ * @addr: DMA address of data buffer
+ * @ctrl: Control and status bits
+ */
+struct macb_dma_desc {
 	u32	addr;
 	u32	ctrl;
 };
@@ -427,7 +432,12 @@ struct dma_desc {
 #define MACB_TX_USED_OFFSET			31
 #define MACB_TX_USED_SIZE			1
 
-struct ring_info {
+/**
+ * struct macb_tx_skb - data about an skb which is being transmitted
+ * @skb: skb currently being transmitted
+ * @mapping: DMA address of the skb's data buffer
+ */
+struct macb_tx_skb {
 	struct sk_buff		*skb;
 	dma_addr_t		mapping;
 };
@@ -512,12 +522,12 @@ struct macb {
 	void __iomem		*regs;
 
 	unsigned int		rx_tail;
-	struct dma_desc		*rx_ring;
+	struct macb_dma_desc	*rx_ring;
 	void			*rx_buffers;
 
 	unsigned int		tx_head, tx_tail;
-	struct dma_desc		*tx_ring;
-	struct ring_info	*tx_skb;
+	struct macb_dma_desc	*tx_ring;
+	struct macb_tx_skb	*tx_skb;
 
 	spinlock_t		lock;
 	struct platform_device	*pdev;
@@ -535,8 +545,6 @@ struct macb {
 	dma_addr_t		tx_ring_dma;
 	dma_addr_t		rx_buffers_dma;
 
-	unsigned int		rx_pending, tx_pending;
-
 	struct mii_bus		*mii_bus;
 	struct phy_device	*phy_dev;
 	unsigned int 		link;