tg3: Clarify rx buffer relationships

This patch attempts to document the various rx buffer sizes used by the
driver and how they relate to each other.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 19 deletions

diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index 5e74a19e7c12..a2a5f318315b 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -125,8 +125,15 @@
                                  TG3_TX_RING_SIZE)
 #define NEXT_TX(N)              (((N) + 1) & (TG3_TX_RING_SIZE - 1))
 
-#define RX_PKT_BUF_SZ           (1536 + tp->rx_offset + 64)
-#define RX_JUMBO_PKT_BUF_SZ     (9046 + tp->rx_offset + 64)
+#define TG3_DMA_BYTE_ENAB               64
+
+#define TG3_RX_STD_DMA_SZ               1536
+#define TG3_RX_JMB_DMA_SZ               9046
+
+#define TG3_RX_DMA_TO_MAP_SZ(x)         ((x) + TG3_DMA_BYTE_ENAB)
+
+#define TG3_RX_STD_MAP_SZ               TG3_RX_DMA_TO_MAP_SZ(TG3_RX_STD_DMA_SZ)
+#define TG3_RX_JMB_MAP_SZ               TG3_RX_DMA_TO_MAP_SZ(TG3_RX_JMB_DMA_SZ)
 
 /* minimum number of free TX descriptors required to wake up TX process */
 #define TG3_TX_WAKEUP_THRESH(tp)                ((tp)->tx_pending / 4)
@@ -4354,7 +4361,7 @@ static int tg3_alloc_rx_skb(struct tg3 *tp, u32 opaque_key,
                 map = &tp->rx_std_buffers[dest_idx];
                 if (src_idx >= 0)
                         src_map = &tp->rx_std_buffers[src_idx];
-                skb_size = tp->rx_pkt_buf_sz;
+                skb_size = tp->rx_pkt_map_sz;
                 break;
 
         case RXD_OPAQUE_RING_JUMBO:
@@ -4363,7 +4370,7 @@ static int tg3_alloc_rx_skb(struct tg3 *tp, u32 opaque_key,
                 map = &tp->rx_jumbo_buffers[dest_idx];
                 if (src_idx >= 0)
                         src_map = &tp->rx_jumbo_buffers[src_idx];
-                skb_size = RX_JUMBO_PKT_BUF_SZ;
+                skb_size = TG3_RX_JMB_MAP_SZ;
                 break;
 
         default:
@@ -4376,14 +4383,13 @@ static int tg3_alloc_rx_skb(struct tg3 *tp, u32 opaque_key,
          * Callers depend upon this behavior and assume that
          * we leave everything unchanged if we fail.
          */
-        skb = netdev_alloc_skb(tp->dev, skb_size);
+        skb = netdev_alloc_skb(tp->dev, skb_size + tp->rx_offset);
         if (skb == NULL)
                 return -ENOMEM;
 
         skb_reserve(skb, tp->rx_offset);
 
-        mapping = pci_map_single(tp->pdev, skb->data,
-                                 skb_size - tp->rx_offset,
+        mapping = pci_map_single(tp->pdev, skb->data, skb_size,
                                  PCI_DMA_FROMDEVICE);
 
         map->skb = skb;
@@ -4540,8 +4546,7 @@ static int tg3_rx(struct tg3 *tp, int budget)
                         if (skb_size < 0)
                                 goto drop_it;
 
-                        pci_unmap_single(tp->pdev, dma_addr,
-                                         skb_size - tp->rx_offset,
+                        pci_unmap_single(tp->pdev, dma_addr, skb_size,
                                          PCI_DMA_FROMDEVICE);
 
                         skb_put(skb, len);
@@ -5531,7 +5536,7 @@ static void tg3_free_rings(struct tg3 *tp)
                         continue;
                 pci_unmap_single(tp->pdev,
                                  pci_unmap_addr(rxp, mapping),
-                                 tp->rx_pkt_buf_sz - tp->rx_offset,
+                                 tp->rx_pkt_map_sz,
                                  PCI_DMA_FROMDEVICE);
                 dev_kfree_skb_any(rxp->skb);
                 rxp->skb = NULL;
@@ -5544,7 +5549,7 @@ static void tg3_free_rings(struct tg3 *tp)
                         continue;
                 pci_unmap_single(tp->pdev,
                                  pci_unmap_addr(rxp, mapping),
-                                 RX_JUMBO_PKT_BUF_SZ - tp->rx_offset,
+                                 TG3_RX_JMB_MAP_SZ,
                                  PCI_DMA_FROMDEVICE);
                 dev_kfree_skb_any(rxp->skb);
                 rxp->skb = NULL;
@@ -5581,7 +5586,7 @@ static void tg3_free_rings(struct tg3 *tp)
  */
 static int tg3_init_rings(struct tg3 *tp)
 {
-        u32 i;
+        u32 i, rx_pkt_dma_sz;
 
         /* Free up all the SKBs. */
         tg3_free_rings(tp);
@@ -5592,10 +5597,11 @@ static int tg3_init_rings(struct tg3 *tp)
         memset(tp->rx_rcb, 0, TG3_RX_RCB_RING_BYTES(tp));
         memset(tp->tx_ring, 0, TG3_TX_RING_BYTES);
 
-        tp->rx_pkt_buf_sz = RX_PKT_BUF_SZ;
+        rx_pkt_dma_sz = TG3_RX_STD_DMA_SZ;
         if ((tp->tg3_flags2 & TG3_FLG2_5780_CLASS) &&
-            (tp->dev->mtu > ETH_DATA_LEN))
-                tp->rx_pkt_buf_sz = RX_JUMBO_PKT_BUF_SZ;
+            tp->dev->mtu > ETH_DATA_LEN)
+                rx_pkt_dma_sz = TG3_RX_JMB_DMA_SZ;
+        tp->rx_pkt_map_sz = TG3_RX_DMA_TO_MAP_SZ(rx_pkt_dma_sz);
 
         /* Initialize invariants of the rings, we only set this
          * stuff once.  This works because the card does not
@@ -5605,8 +5611,7 @@ static int tg3_init_rings(struct tg3 *tp)
                 struct tg3_rx_buffer_desc *rxd;
 
                 rxd = &tp->rx_std[i];
-                rxd->idx_len = (tp->rx_pkt_buf_sz - tp->rx_offset - 64)
-                        << RXD_LEN_SHIFT;
+                rxd->idx_len = rx_pkt_dma_sz << RXD_LEN_SHIFT;
                 rxd->type_flags = (RXD_FLAG_END << RXD_FLAGS_SHIFT);
                 rxd->opaque = (RXD_OPAQUE_RING_STD |
                                (i << RXD_OPAQUE_INDEX_SHIFT));
@@ -5617,8 +5622,7 @@ static int tg3_init_rings(struct tg3 *tp)
                         struct tg3_rx_buffer_desc *rxd;
 
                         rxd = &tp->rx_jumbo[i];
-                        rxd->idx_len = (RX_JUMBO_PKT_BUF_SZ - tp->rx_offset - 64)
-                                << RXD_LEN_SHIFT;
+                        rxd->idx_len = TG3_RX_JMB_DMA_SZ << RXD_LEN_SHIFT;
                         rxd->type_flags = (RXD_FLAG_END << RXD_FLAGS_SHIFT) |
                                 RXD_FLAG_JUMBO;
                         rxd->opaque = (RXD_OPAQUE_RING_JUMBO |