net: ep93xx_eth: fix DMA API violations
Mika Westerberg [Sat, 11 Jun 2011 08:39:58 +0000 (08:39 +0000)]
Russell King said:
>
> So, to summarize what its doing:
>
> 1. It allocates buffers for rx and tx.
> 2. It maps them with dma_map_single().
>       This transfers ownership of the buffer to the DMA device.
> 3. In ep93xx_xmit,
> 3a. It copies the data into the buffer with skb_copy_and_csum_dev()
>       This violates the DMA buffer ownership rules - the CPU should
>       not be writing to this buffer while it is (in principle) owned
>       by the DMA device.
> 3b. It then calls dma_sync_single_for_cpu() for the buffer.
>       This transfers ownership of the buffer to the CPU, which surely
>       is the wrong direction.
> 4. In ep93xx_rx,
> 4a. It calls dma_sync_single_for_cpu() for the buffer.
>       This at least transfers the DMA buffer ownership to the CPU
>       before the CPU reads the buffer
> 4b. It then uses skb_copy_to_linear_data() to copy the data out.
>       At no point does it transfer ownership back to the DMA device.
> 5. When the driver is removed, it dma_unmap_single()'s the buffer.
>       This transfers ownership of the buffer to the CPU.
> 6. It frees the buffer.
>
> While it may work on ep93xx, it's not respecting the DMA API rules,
> and with DMA debugging enabled it will probably encounter quite a few
> warnings.

This patch fixes these violations.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Tested-by: Petr Stetiar <ynezz@true.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/arm/ep93xx_eth.c

index bef3811..0b46b8e 100644 (file)
@@ -283,10 +283,14 @@ static int ep93xx_rx(struct net_device *dev, int processed, int budget)
 
                skb = dev_alloc_skb(length + 2);
                if (likely(skb != NULL)) {
+                       struct ep93xx_rdesc *rxd = &ep->descs->rdesc[entry];
                        skb_reserve(skb, 2);
-                       dma_sync_single_for_cpu(dev->dev.parent, ep->descs->rdesc[entry].buf_addr,
+                       dma_sync_single_for_cpu(dev->dev.parent, rxd->buf_addr,
                                                length, DMA_FROM_DEVICE);
                        skb_copy_to_linear_data(skb, ep->rx_buf[entry], length);
+                       dma_sync_single_for_device(dev->dev.parent,
+                                                  rxd->buf_addr, length,
+                                                  DMA_FROM_DEVICE);
                        skb_put(skb, length);
                        skb->protocol = eth_type_trans(skb, dev);
 
@@ -348,6 +352,7 @@ poll_some_more:
 static int ep93xx_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        struct ep93xx_priv *ep = netdev_priv(dev);
+       struct ep93xx_tdesc *txd;
        int entry;
 
        if (unlikely(skb->len > MAX_PKT_SIZE)) {
@@ -359,11 +364,14 @@ static int ep93xx_xmit(struct sk_buff *skb, struct net_device *dev)
        entry = ep->tx_pointer;
        ep->tx_pointer = (ep->tx_pointer + 1) & (TX_QUEUE_ENTRIES - 1);
 
-       ep->descs->tdesc[entry].tdesc1 =
-               TDESC1_EOF | (entry << 16) | (skb->len & 0xfff);
+       txd = &ep->descs->tdesc[entry];
+
+       txd->tdesc1 = TDESC1_EOF | (entry << 16) | (skb->len & 0xfff);
+       dma_sync_single_for_cpu(dev->dev.parent, txd->buf_addr, skb->len,
+                               DMA_TO_DEVICE);
        skb_copy_and_csum_dev(skb, ep->tx_buf[entry]);
-       dma_sync_single_for_cpu(dev->dev.parent, ep->descs->tdesc[entry].buf_addr,
-                               skb->len, DMA_TO_DEVICE);
+       dma_sync_single_for_device(dev->dev.parent, txd->buf_addr, skb->len,
+                                  DMA_TO_DEVICE);
        dev_kfree_skb(skb);
 
        spin_lock_irq(&ep->tx_pending_lock);