From 2488a54e485bc108ab136e8e3cb95b99e97f68b5 Mon Sep 17 00:00:00 2001 From: Sebastian Siewior Date: Mon, 2 Dec 2013 10:52:55 +0100 Subject: [PATCH] net: fec_main: dma_map() only the length of the skb On tx submit the driver always dma_map_single() FEC_ENET_TX_FRSIZE (=2048) bytes. This works because we don't overwrite any memory after the data buffer, we remove it from cache if it was there. So we hurt performace in case the mapping of a smaller area makes a difference. There is also a bug: If the data area starts shortly before the end of RAM say 0xc7fffa10 and the RAM ends at 0xc8000000 then we have enough space to fit the data area (according to skb->len) but we would map beyond end of ram if we are using 2048. In v2.6.31 (against which kernel this patch made) there is the following check in dma_cache_maint(): |BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1)); Since the area starting at 0xc8000000 is no longer virt_addr_valid() we BUG() during dma_map_single(). The BUG() statement was removed in v3.5-rc1 as per 2dc6a016 ("ARM: dma-mapping: use asm-generic/dma-mapping-common.h"). This patch was tested on v2.6.31 and then forward-ported and compile tested only against the net tree. I think it is still worth fixing mainline even after the BUG() statement is gone. Tested-by: Fugang Duan Cc: Marek Szyprowski Signed-off-by: Sebastian Andrzej Siewior Acked-by: Fugang Duan Signed-off-by: David S. Miller --- drivers/net/ethernet/freescale/fec_main.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c index 4cbebf3..73b000d 100644 --- a/drivers/net/ethernet/freescale/fec_main.c +++ b/drivers/net/ethernet/freescale/fec_main.c @@ -385,7 +385,7 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev) * data. */ bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev, bufaddr, - FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); + skb->len, DMA_TO_DEVICE); if (dma_mapping_error(&fep->pdev->dev, bdp->cbd_bufaddr)) { bdp->cbd_bufaddr = 0; fep->tx_skbuff[index] = NULL; @@ -779,11 +779,10 @@ fec_enet_tx(struct net_device *ndev) else index = bdp - fep->tx_bd_base; - dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, - FEC_ENET_TX_FRSIZE, DMA_TO_DEVICE); - bdp->cbd_bufaddr = 0; - skb = fep->tx_skbuff[index]; + dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr, skb->len, + DMA_TO_DEVICE); + bdp->cbd_bufaddr = 0; /* Check for errors. */ if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC | -- 2.7.4