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BUG in the PCNET32 ethernet driver

To: Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, tsbogend@alpha.franken.de, linux-net@vger.kernel.org, kevink@mips.com
Subject: BUG in the PCNET32 ethernet driver
From: Carsten Langgaard <carstenl@mips.com>
Date: Wed, 13 Nov 2002 14:34:48 +0100
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
I finally found the problem that caused a lot of problem with an
ethernet throughput test, that we have been running.
It turned out the problem is related to a bug in the PCNET32 driver,
when you are running it on a system that doesn't support hardware
coherency.

The problem is the way the AMD ethernet driver is using the PCI DMA
mapping routines.
When the driver releases a receive DMA buffer to the controller for
later DMA transfer it call the PCI DMA flushing routine as it should,
but it calls it with a length equal to 0. The driver is assuming that
the length field in the buffer structure is equal to the actual length
of the buffer, but this field is first updated when we are receiving the
packet (and call the skb_put function).

I have attached a patch, that solve this problem.
Please note that the patch is against Ralf Baechle latest linux_2_4
tree.

/Carsten



--
_    _ ____  ___   Carsten Langgaard   Mailto:carstenl@mips.com
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Index: drivers/net/pcnet32.c
===================================================================
RCS file: /home/cvs/linux/drivers/net/pcnet32.c,v
retrieving revision 1.33.2.3
diff -u -r1.33.2.3 pcnet32.c
--- drivers/net/pcnet32.c       6 Oct 2002 20:49:43 -0000       1.33.2.3
+++ drivers/net/pcnet32.c       13 Nov 2002 13:32:09 -0000
@@ -981,7 +981,7 @@
            }
            skb_reserve (rx_skbuff, 2);
        }
-        lp->rx_dma_addr[i] = pci_map_single(lp->pci_dev, rx_skbuff->tail, 
rx_skbuff->len, PCI_DMA_FROMDEVICE);
+        lp->rx_dma_addr[i] = pci_map_single(lp->pci_dev, rx_skbuff->tail, 
PKT_BUF_SZ, PCI_DMA_FROMDEVICE);
        lp->rx_ring[i].base = (u32)le32_to_cpu(lp->rx_dma_addr[i]);
        lp->rx_ring[i].buf_length = le16_to_cpu(-PKT_BUF_SZ);
        lp->rx_ring[i].status = le16_to_cpu(0x8000);
@@ -1316,13 +1316,13 @@
                    if ((newskb = dev_alloc_skb (PKT_BUF_SZ))) {
                        skb_reserve (newskb, 2);
                        skb = lp->rx_skbuff[entry];
-                       pci_unmap_single(lp->pci_dev, lp->rx_dma_addr[entry], 
skb->len, PCI_DMA_FROMDEVICE);
+                       pci_unmap_single(lp->pci_dev, lp->rx_dma_addr[entry], 
pkt_len +2, PCI_DMA_FROMDEVICE);
                        skb_put (skb, pkt_len);
                        lp->rx_skbuff[entry] = newskb;
                        newskb->dev = dev;
                         lp->rx_dma_addr[entry] = 
                                pci_map_single(lp->pci_dev, newskb->tail,
-                                       newskb->len, PCI_DMA_FROMDEVICE);
+                                       PKT_BUF_SZ, PCI_DMA_FROMDEVICE);
                        lp->rx_ring[entry].base = 
le32_to_cpu(lp->rx_dma_addr[entry]);
                        rx_in_place = 1;
                    } else
@@ -1349,13 +1349,10 @@
                if (!rx_in_place) {
                    skb_reserve(skb,2); /* 16 byte align */
                    skb_put(skb,pkt_len);       /* Make room */
-                    pci_dma_sync_single(lp->pci_dev, 
-                                   lp->rx_dma_addr[entry],
-                                   pkt_len,
-                                   PCI_DMA_FROMDEVICE);
                    eth_copy_and_sum(skb,
                                     (unsigned char 
*)(lp->rx_skbuff[entry]->tail),
                                     pkt_len,0);
+                   lp->rx_dma_addr[entry] = pci_map_single(lp->pci_dev, 
lp->rx_skbuff[entry]->tail, PKT_BUF_SZ, PCI_DMA_FROMDEVICE);
                }
                lp->stats.rx_bytes += skb->len;
                skb->protocol=eth_type_trans(skb,dev);
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