stmmac: review RX/TX ring management

This patch is to rework the ring management now optimized.
The indexes into the ring buffer are always incremented, and
the entry is accessed via doing a modulo to find the "real"
position in the ring.
It is inefficient, modulo is an expensive operation.

The formula [(entry + 1) & (size - 1)] is now adopted on
a ring that is power-of-2 in size.
Then, the number of elements cannot be set by command line but
it is fixed.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/chain_mode.c

@@ -31,8 +31,7 @@
 static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 {
 	struct stmmac_priv *priv = (struct stmmac_priv *)p;
-	unsigned int txsize = priv->dma_tx_size;
-	unsigned int entry = priv->cur_tx % txsize;
+	unsigned int entry = priv->cur_tx;
 	struct dma_desc *desc = priv->dma_tx + entry;
 	unsigned int nopaged_len = skb_headlen(skb);
 	unsigned int bmax;
@@ -54,7 +53,7 @@ static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 
 	while (len != 0) {
 		priv->tx_skbuff[entry] = NULL;
-		entry = (++priv->cur_tx) % txsize;
+		entry = STMMAC_GET_ENTRY(entry, DMA_TX_SIZE);
 		desc = priv->dma_tx + entry;
 
 		if (len > bmax) {
@@ -82,6 +81,9 @@ static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 			len = 0;
 		}
 	}
+
+	priv->cur_tx = entry;
+
 	return entry;
 }
 
@@ -138,7 +140,7 @@ static void stmmac_refill_desc3(void *priv_ptr, struct dma_desc *p)
 		 */
 		p->des3 = (unsigned int)(priv->dma_rx_phy +
 					 (((priv->dirty_rx) + 1) %
-					  priv->dma_rx_size) *
+					  DMA_RX_SIZE) *
 					 sizeof(struct dma_desc));
 }
 
@@ -151,10 +153,9 @@ static void stmmac_clean_desc3(void *priv_ptr, struct dma_desc *p)
 		 * 1588-2002 time stamping is enabled, hence reinitialize it
 		 * to keep explicit chaining in the descriptor.
 		 */
-		p->des3 = (unsigned int)(priv->dma_tx_phy +
-					 (((priv->dirty_tx + 1) %
-					   priv->dma_tx_size) *
-					  sizeof(struct dma_desc)));
+		p->des3 = (unsigned int)((priv->dma_tx_phy +
+					  ((priv->dirty_tx + 1) % DMA_TX_SIZE))
+					  * sizeof(struct dma_desc));
 }
 
 const struct stmmac_mode_ops chain_mode_ops = {

drivers/net/ethernet/stmicro/stmmac/common.h

@@ -42,6 +42,10 @@
 #define	DWMAC_CORE_3_40	0x34
 #define	DWMAC_CORE_3_50	0x35
 
+#define DMA_TX_SIZE 512
+#define DMA_RX_SIZE 512
+#define STMMAC_GET_ENTRY(x, size)	((x + 1) & (size - 1))
+
 #undef FRAME_FILTER_DEBUG
 /* #define FRAME_FILTER_DEBUG */
 

drivers/net/ethernet/stmicro/stmmac/ring_mode.c

@@ -31,8 +31,7 @@
 static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 {
 	struct stmmac_priv *priv = (struct stmmac_priv *)p;
-	unsigned int txsize = priv->dma_tx_size;
-	unsigned int entry = priv->cur_tx % txsize;
+	unsigned int entry = priv->cur_tx;
 	struct dma_desc *desc;
 	unsigned int nopaged_len = skb_headlen(skb);
 	unsigned int bmax, len;
@@ -62,7 +61,7 @@ static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 						STMMAC_RING_MODE);
 		wmb();
 		priv->tx_skbuff[entry] = NULL;
-		entry = (++priv->cur_tx) % txsize;
+		entry = STMMAC_GET_ENTRY(entry, DMA_TX_SIZE);
 
 		if (priv->extend_desc)
 			desc = (struct dma_desc *)(priv->dma_etx + entry);
@@ -90,6 +89,8 @@ static int stmmac_jumbo_frm(void *p, struct sk_buff *skb, int csum)
 						STMMAC_RING_MODE);
 	}
 
+	priv->cur_tx = entry;
+
 	return entry;
 }
 

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -54,7 +54,6 @@ struct stmmac_priv {
 	struct sk_buff **tx_skbuff;
 	unsigned int cur_tx;
 	unsigned int dirty_tx;
-	unsigned int dma_tx_size;
 	u32 tx_count_frames;
 	u32 tx_coal_frames;
 	u32 tx_coal_timer;
@@ -71,7 +70,6 @@ struct stmmac_priv {
 	struct sk_buff **rx_skbuff;
 	unsigned int cur_rx;
 	unsigned int dirty_rx;
-	unsigned int dma_rx_size;
 	unsigned int dma_buf_sz;
 	u32 rx_riwt;
 	int hwts_rx_en;