Spidernet DMA coalescing

The current driver code performs 512 DMA mappings of a bunch of
32-byte ring descriptor structures. This is silly, as they are
all in contiguous memory. This patch changes the code to
dma_map_coherent() each rx/tx ring as a whole.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: James K Lewis <jklewis@us.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 47 insertions, 56 deletions

diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c
index 8ea2fc1b96cb..8c8381cbce0a 100644
--- a/drivers/net/spider_net.c
+++ b/drivers/net/spider_net.c
@@ -280,72 +280,67 @@ spider_net_free_chain(struct spider_net_card *card,
 {
         struct spider_net_descr *descr;
 
-        for (descr = chain->tail; !descr->bus_addr; descr = descr->next) {
-                pci_unmap_single(card->pdev, descr->bus_addr,
-                                 SPIDER_NET_DESCR_SIZE, PCI_DMA_BIDIRECTIONAL);
+        descr = chain->ring;
+        do {
                 descr->bus_addr = 0;
-        }
+                descr->next_descr_addr = 0;
+                descr = descr->next;
+        } while (descr != chain->ring);
+
+        dma_free_coherent(&card->pdev->dev, chain->num_desc,
+            chain->ring, chain->dma_addr);
 }
 
 /**
- * spider_net_init_chain - links descriptor chain
+ * spider_net_init_chain - alloc and link descriptor chain
  * @card: card structure
  * @chain: address of chain
- * @start_descr: address of descriptor array
- * @no: number of descriptors
  *
- * we manage a circular list that mirrors the hardware structure,
+ * We manage a circular list that mirrors the hardware structure,
  * except that the hardware uses bus addresses.
  *
- * returns 0 on success, <0 on failure
+ * Returns 0 on success, <0 on failure
  */
 static int
 spider_net_init_chain(struct spider_net_card *card,
-                       struct spider_net_descr_chain *chain,
-                       struct spider_net_descr *start_descr,
-                       int no)
+                       struct spider_net_descr_chain *chain)
 {
         int i;
         struct spider_net_descr *descr;
         dma_addr_t buf;
+        size_t alloc_size;
 
-        descr = start_descr;
-        memset(descr, 0, sizeof(*descr) * no);
+        alloc_size = chain->num_desc * sizeof (struct spider_net_descr);
 
-        /* set up the hardware pointers in each descriptor */
-        for (i=0; i<no; i++, descr++) {
-                descr->dmac_cmd_status = SPIDER_NET_DESCR_NOT_IN_USE;
+        chain->ring = dma_alloc_coherent(&card->pdev->dev, alloc_size,
+                &chain->dma_addr, GFP_KERNEL);
 
-                buf = pci_map_single(card->pdev, descr,
-                                     SPIDER_NET_DESCR_SIZE,
-                                     PCI_DMA_BIDIRECTIONAL);
+        if (!chain->ring)
+                return -ENOMEM;
 
-                if (pci_dma_mapping_error(buf))
-                        goto iommu_error;
+        descr = chain->ring;
+        memset(descr, 0, alloc_size);
+
+        /* Set up the hardware pointers in each descriptor */
+        buf = chain->dma_addr;
+        for (i=0; i < chain->num_desc; i++, descr++) {
+                descr->dmac_cmd_status = SPIDER_NET_DESCR_NOT_IN_USE;
 
                 descr->bus_addr = buf;
+                descr->next_descr_addr = 0;
                 descr->next = descr + 1;
                 descr->prev = descr - 1;
 
+                buf += sizeof(struct spider_net_descr);
         }
         /* do actual circular list */
-        (descr-1)->next = start_descr;
-        start_descr->prev = descr-1;
+        (descr-1)->next = chain->ring;
+        chain->ring->prev = descr-1;
 
         spin_lock_init(&chain->lock);
-        chain->head = start_descr;
-        chain->tail = start_descr;
-
+        chain->head = chain->ring;
+        chain->tail = chain->ring;
         return 0;
-
-iommu_error:
-        descr = start_descr;
-        for (i=0; i < no; i++, descr++)
-                if (descr->bus_addr)
-                        pci_unmap_single(card->pdev, descr->bus_addr,
-                                         SPIDER_NET_DESCR_SIZE,
-                                         PCI_DMA_BIDIRECTIONAL);
-        return -ENOMEM;
 }
 
 /**
@@ -707,7 +702,7 @@ spider_net_set_low_watermark(struct spider_net_card *card)
         }
 
         /* If TX queue is short, don't even bother with interrupts */
-        if (cnt < card->num_tx_desc/4)
+        if (cnt < card->tx_chain.num_desc/4)
                 return cnt;
 
         /* Set low-watermark 3/4th's of the way into the queue. */
@@ -1652,26 +1647,25 @@ spider_net_open(struct net_device *netdev)
 {
         struct spider_net_card *card = netdev_priv(netdev);
         struct spider_net_descr *descr;
-        int i, result;
+        int result;
 
-        result = -ENOMEM;
-        if (spider_net_init_chain(card, &card->tx_chain, card->descr,
-                                  card->num_tx_desc))
+        result = spider_net_init_chain(card, &card->tx_chain);
+        if (result)
                 goto alloc_tx_failed;
-
         card->low_watermark = NULL;
 
-        /* rx_chain is after tx_chain, so offset is descr + tx_count */
-        if (spider_net_init_chain(card, &card->rx_chain,
-                                  card->descr + card->num_tx_desc,
-                                  card->num_rx_desc))
+        result = spider_net_init_chain(card, &card->rx_chain);
+        if (result)
                 goto alloc_rx_failed;
 
-        descr = card->rx_chain.head;
-        for (i=0; i < card->num_rx_desc; i++, descr++)
+        /* Make a ring of of bus addresses */
+        descr = card->rx_chain.ring;
+        do {
                 descr->next_descr_addr = descr->next->bus_addr;
+                descr = descr->next;
+        } while (descr != card->rx_chain.ring);
 
-        /* allocate rx skbs */
+        /* Allocate rx skbs */
         if (spider_net_alloc_rx_skbs(card))
                 goto alloc_skbs_failed;
 
@@ -1924,6 +1918,7 @@ spider_net_stop(struct net_device *netdev)
 
         /* release chains */
         spider_net_release_tx_chain(card, 1);
+        spider_net_free_rx_chain_contents(card);
 
         spider_net_free_rx_chain_contents(card);
 
@@ -2057,8 +2052,8 @@ spider_net_setup_netdev(struct spider_net_card *card)
 
         card->options.rx_csum = SPIDER_NET_RX_CSUM_DEFAULT;
 
-        card->num_tx_desc = tx_descriptors;
-        card->num_rx_desc = rx_descriptors;
+        card->tx_chain.num_desc = tx_descriptors;
+        card->rx_chain.num_desc = rx_descriptors;
 
         spider_net_setup_netdev_ops(netdev);
 
@@ -2107,12 +2102,8 @@ spider_net_alloc_card(void)
 {
         struct net_device *netdev;
         struct spider_net_card *card;
-        size_t alloc_size;
 
-        alloc_size = sizeof (*card) +
-                sizeof (struct spider_net_descr) * rx_descriptors +
-                sizeof (struct spider_net_descr) * tx_descriptors;
-        netdev = alloc_etherdev(alloc_size);
+        netdev = alloc_etherdev(sizeof(struct spider_net_card));
         if (!netdev)
                 return NULL;