pasemi_mac: Fix TX ring wrap checking

The old logic didn't detect full (tx) ring cases properly, causing
overruns and general badness. Clean it up a bit and abstract out the
ring size checks, always making sure to leave 1 slot open.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

2 files changed, 15 insertions, 12 deletions

diff --git a/drivers/net/pasemi_mac.c b/drivers/net/pasemi_mac.c
index 4836d405cd5d..dc710a0826b2 100644
--- a/drivers/net/pasemi_mac.c
+++ b/drivers/net/pasemi_mac.c
@@ -69,6 +69,10 @@
 #define RX_DESC_INFO(mac, num)  ((mac)->rx->desc_info[(num) & (RX_RING_SIZE-1)])
 #define RX_BUFF(mac, num)       ((mac)->rx->buffers[(num) & (RX_RING_SIZE-1)])
 
+#define RING_USED(ring)         (((ring)->next_to_fill - (ring)->next_to_clean) \
+                                 & ((ring)->size - 1))
+#define RING_AVAIL(ring)        ((ring->size) - RING_USED(ring))
+
 #define BUF_SIZE 1646 /* 1500 MTU + ETH_HLEN + VLAN_HLEN + 2 64B cachelines */
 
 MODULE_LICENSE("GPL");
@@ -174,6 +178,7 @@ static int pasemi_mac_setup_rx_resources(struct net_device *dev)
 
         spin_lock_init(&ring->lock);
 
+        ring->size = RX_RING_SIZE;
         ring->desc_info = kzalloc(sizeof(struct pasemi_mac_buffer) *
                                   RX_RING_SIZE, GFP_KERNEL);
 
@@ -253,6 +258,7 @@ static int pasemi_mac_setup_tx_resources(struct net_device *dev)
 
         spin_lock_init(&ring->lock);
 
+        ring->size = TX_RING_SIZE;
         ring->desc_info = kzalloc(sizeof(struct pasemi_mac_buffer) *
                                   TX_RING_SIZE, GFP_KERNEL);
         if (!ring->desc_info)
@@ -281,7 +287,7 @@ static int pasemi_mac_setup_tx_resources(struct net_device *dev)
                            PAS_DMA_TXCHAN_CFG_UP |
                            PAS_DMA_TXCHAN_CFG_WT(2));
 
-        ring->next_to_use = 0;
+        ring->next_to_fill = 0;
         ring->next_to_clean = 0;
 
         snprintf(ring->irq_name, sizeof(ring->irq_name),
@@ -376,9 +382,7 @@ static void pasemi_mac_replenish_rx_ring(struct net_device *dev)
         int start = mac->rx->next_to_fill;
         unsigned int limit, count;
 
-        limit = (mac->rx->next_to_clean + RX_RING_SIZE -
-                 mac->rx->next_to_fill) & (RX_RING_SIZE - 1);
-
+        limit = RING_AVAIL(mac->rx);
         /* Check to see if we're doing first-time setup */
         if (unlikely(mac->rx->next_to_clean == 0 && mac->rx->next_to_fill == 0))
                 limit = RX_RING_SIZE;
@@ -562,7 +566,7 @@ restart:
         spin_lock_irqsave(&mac->tx->lock, flags);
 
         start = mac->tx->next_to_clean;
-        limit = min(mac->tx->next_to_use, start+32);
+        limit = min(mac->tx->next_to_fill, start+32);
 
         count = 0;
 
@@ -1004,14 +1008,13 @@ static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
 
         spin_lock_irqsave(&txring->lock, flags);
 
-        if (txring->next_to_clean - txring->next_to_use == TX_RING_SIZE) {
+        if (RING_AVAIL(txring) <= 1) {
                 spin_unlock_irqrestore(&txring->lock, flags);
                 pasemi_mac_clean_tx(mac);
                 pasemi_mac_restart_tx_intr(mac);
                 spin_lock_irqsave(&txring->lock, flags);
 
-                if (txring->next_to_clean - txring->next_to_use ==
-                    TX_RING_SIZE) {
+                if (RING_AVAIL(txring) <= 1) {
                         /* Still no room -- stop the queue and wait for tx
                          * intr when there's room.
                          */
@@ -1020,15 +1023,15 @@ static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
                 }
         }
 
-        dp = &TX_DESC(mac, txring->next_to_use);
-        info = &TX_DESC_INFO(mac, txring->next_to_use);
+        dp = &TX_DESC(mac, txring->next_to_fill);
+        info = &TX_DESC_INFO(mac, txring->next_to_fill);
 
         dp->mactx = mactx;
         dp->ptr   = ptr;
         info->dma = map;
         info->skb = skb;
 
-        txring->next_to_use++;
+        txring->next_to_fill++;
         mac->stats.tx_packets++;
         mac->stats.tx_bytes += skb->len;
 
diff --git a/drivers/net/pasemi_mac.h b/drivers/net/pasemi_mac.h
index fbbc17a31db7..c5b0adbc182e 100644
--- a/drivers/net/pasemi_mac.h
+++ b/drivers/net/pasemi_mac.h
@@ -31,7 +31,7 @@ struct pasemi_mac_txring {
         struct pas_dma_xct_descr        *desc;
         dma_addr_t       dma;
         unsigned int     size;
-        unsigned int     next_to_use;
+        unsigned int     next_to_fill;
         unsigned int     next_to_clean;
         struct pasemi_mac_buffer *desc_info;
         char             irq_name[10];  /* "eth%d tx" */