netdev - RE: [PATCH] net: fec_main: dma_map() only the length of the skb

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Date:	Thu, 28 Nov 2013 01:18:09 +0000
From:	Fugang Duan <fugang.duan@...escale.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Fabio Estevam <Fabio.Estevam@...escale.com>,
	Frank Li <frank.li@...escale.net>,
	Jim Baxter <jim_baxter@...tor.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: RE: [PATCH] net: fec_main: dma_map() only the length of the skb

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Sent: Wednesday, November 27, 2013 9:38 PM

>To: Duan Fugang-B38611
>Cc: netdev@...r.kernel.org; David S. Miller; Estevam Fabio-R49496; Frank Li;
>Jim Baxter; Marek Szyprowski
>Subject: Re: [PATCH] net: fec_main: dma_map() only the length of the skb
>
>- <frank.li@...escale.net> because MTA complains
>
>On 11/27/2013 02:08 PM, Fugang Duan wrote:
>> In fact, there have one memory copy for enet as below since enet have 16
>bytes data buffer alignment request.
>> if (((unsigned long) bufaddr) & FEC_ALIGNMENT) {
>>                 memcpy(fep->tx_bounce[index], skb->data, skb->len);
>>                 bufaddr = fep->tx_bounce[index]; }
>
>This memcpy() is only executed if the buffer isn't properly aligned which
>shouldn't be the rule but an exception. This aligment check is also available
>in v2.6.31 where the BUG_ON() statement was triggered.
>
In fact, the skb->data address is not aligned with FEC_ALIGNMENT, so memcpy() always is called at here.

Thanks,
Andy 

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