netdev - Re: [PATCH 06/11] de2104x: fix DMA sync

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Message-ID: <20100122010244.GA27529@lackof.org>
Date:	Thu, 21 Jan 2010 18:02:44 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>,
	Jarek Poplawski <jarkao2@...il.com>,
	Grant Grundler <grundler@...isc-linux.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 06/11] de2104x: fix DMA sync_single length error

On Wed, Jan 20, 2010 at 12:45:05PM -0800, Stephen Hemminger wrote:
> The DMA api requires that the full mapping be sync'd when
> copying frame. First found by Jarek on sky2.

Are you referring to the example code in Documentation/PCI/PCI-DMA-mapping.txt?

I don't see any "Use the full mapping" statement otherwise.

Is there a DMA HW implementation that requires the syncing full buffer?

I think it would be interesting to point that out in the commit comments
since other NIC drivers are likely to also have this issue as well.

I have no objection to this patch. Just want to be clear why
it's being pushed.

Please added Acked-by: Grant Grundler <grundler@...isc-linux.org>

thanks,
grant


> 
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> 
> --- a/drivers/net/tulip/de2104x.c	2010-01-20 11:41:20.878138314 -0800
> +++ b/drivers/net/tulip/de2104x.c	2010-01-20 11:41:59.858847380 -0800
> @@ -456,11 +456,13 @@ static void de_rx (struct de_private *de
>  					       buflen, PCI_DMA_FROMDEVICE);
>  			de->rx_skb[rx_tail].skb = copy_skb;
>  		} else {
> -			pci_dma_sync_single_for_cpu(de->pdev, mapping, len, PCI_DMA_FROMDEVICE);
> +			pci_dma_sync_single_for_cpu(de->pdev, mapping,
> +						    buflen, PCI_DMA_FROMDEVICE);
>  			skb_reserve(copy_skb, RX_OFFSET);
>  			skb_copy_from_linear_data(skb, skb_put(copy_skb, len),
>  						  len);
> -			pci_dma_sync_single_for_device(de->pdev, mapping, len, PCI_DMA_FROMDEVICE);
> +			pci_dma_sync_single_for_device(de->pdev, mapping,
> +						       buflen, PCI_DMA_FROMDEVICE);
>  
>  			/* We'll reuse the original ring buffer. */
>  			skb = copy_skb;
> 
> -- 
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