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Commit f1c089e3 authored by Mika Westerberg's avatar Mika Westerberg Committed by David S. Miller
Browse files

net: ep93xx_eth: fix DMA API violations 



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: default avatarMika Westerberg <mika.westerberg@iki.fi>
Acked-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
Acked-by: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Tested-by: default avatarPetr Stetiar <ynezz@true.cz>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1f758a43

drivers/net/arm/ep93xx_eth.c

+13 −5
Original line number Diff line number Diff line
@@ -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);