[PATCH net-next v2 1/2] net: stmmac: use circ_buf helpers for descriptors

["Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>]

The stmmac descriptor queues are circular buffers, operated as far as
the hardware is concerned as either a ring, or a chain that loops back
on itself. From the software perspective, it forms a circular buffer.

We have a few places which calculate the number of in-use and free
entries in these circular buffers, for which we have macros for.
Use CIRC_CNT() and CIRC_SPACE() as appropriate to calculate these
values.

Validating, for stmmac_tx_avail(), which uses CIRC_SPACE():

  dirty_tx = 1, cur_tx = 0 -> 0
  dirty_tx = 0, cur_tx = 0 -> dma_tx_size - 1
  dirty_tx = 0, cur_tx = 1 -> dma_tx_size - 2

dirty_tx passed as end, reduced by one. cur_tx passed as start.
Output on sane computers is identical.

For stmmac_rx_dirty(), which uses CIRC_CNT():

  dirty_rx = 1, cur_rx = 0 -> dma_rx_size - 1
  dirty_rx = 0, cur_rx = 0 -> 0
  dirty_rx = 0, cur_rx = 1 -> 1

dirty_rx passed as start, cur_rx passed as end. Output is identical.

Same validation performed on the is_last_segment calculation, which
also gets converted to CIRC_CNT().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 23 ++++++-------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a2a0985e8c37..2d74fe98ad61 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -14,6 +14,7 @@
 	https://bugzilla.stlinux.com/
 *******************************************************************************/
 
+#include <linux/circ_buf.h>
 #include <linux/clk.h>
 #include <linux/kernel.h>
 #include <linux/interrupt.h>
@@ -355,14 +356,9 @@ static void print_pkt(unsigned char *buf, int len)
 static inline u32 stmmac_tx_avail(struct stmmac_priv *priv, u32 queue)
 {
 	struct stmmac_tx_queue *tx_q = &priv->dma_conf.tx_queue[queue];
-	u32 avail;
 
-	if (tx_q->dirty_tx > tx_q->cur_tx)
-		avail = tx_q->dirty_tx - tx_q->cur_tx - 1;
-	else
-		avail = priv->dma_conf.dma_tx_size - tx_q->cur_tx + tx_q->dirty_tx - 1;
-
-	return avail;
+	return CIRC_SPACE(tx_q->cur_tx, tx_q->dirty_tx,
+			  priv->dma_conf.dma_tx_size);
 }
 
 /**
@@ -373,14 +369,9 @@ static inline u32 stmmac_tx_avail(struct stmmac_priv *priv, u32 queue)
 static inline u32 stmmac_rx_dirty(struct stmmac_priv *priv, u32 queue)
 {
 	struct stmmac_rx_queue *rx_q = &priv->dma_conf.rx_queue[queue];
-	u32 dirty;
-
-	if (rx_q->dirty_rx <= rx_q->cur_rx)
-		dirty = rx_q->cur_rx - rx_q->dirty_rx;
-	else
-		dirty = priv->dma_conf.dma_rx_size - rx_q->dirty_rx + rx_q->cur_rx;
 
-	return dirty;
+	return CIRC_CNT(rx_q->cur_rx, rx_q->dirty_rx,
+			priv->dma_conf.dma_rx_size);
 }
 
 static bool stmmac_eee_tx_busy(struct stmmac_priv *priv)
@@ -4571,8 +4562,8 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* If we only have one entry used, then the first entry is the last
 	 * segment.
 	 */
-	is_last_segment = ((tx_q->cur_tx - first_entry) &
-			   (priv->dma_conf.dma_tx_size - 1)) == 1;
+	is_last_segment = CIRC_CNT(tx_q->cur_tx, first_entry,
+				   priv->dma_conf.dma_tx_size) == 1;
 
 	/* Complete the first descriptor before granting the DMA */
 	stmmac_prepare_tso_tx_desc(priv, first, 1, proto_hdr_len, 0, 1,
-- 
2.47.3