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

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Message-ID: <5295F5D3.8020002@linutronix.de>
Date:	Wed, 27 Nov 2013 14:38:27 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Fugang Duan <fugang.duan@...escale.com>
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

- <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.

> 
> So, the bug you describe at commit log shouldn't exist.
> 
> Anyway, it is better to use the real packet size for the mapping.
> 
> 
> I will do overnight stress test for the patch tomorrow.

Thanks.

> 
> Thanks,
> Andy
> 

Sebastian
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