linux-kernel - Re: net: fec: fix regression on i.MX28 introduced by rx

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Message-ID: <20141104112912.2be8bf1a@ipc1.ka-ro>
Date:	Tue, 4 Nov 2014 11:29:12 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	David Miller <davem@...emloft.net>
Cc:	Lothar Waßmann <LW@...O-electronics.de>,
	fabio.estevam@...escale.com, Frank.Li@...escale.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	rmk+kernel@....linux.org.uk, linux-arm-kernel@...ts.infradead.org
Subject: Re: net: fec: fix regression on i.MX28 introduced by rx_copybreak
 support

Hi David,

Lothar Waßmann wrote:
> David Miller wrote:
> > From: Lothar Waßmann <LW@...O-electronics.de>
> > Date: Thu, 30 Oct 2014 07:51:04 +0100
> > 
> > >> Also, I don't thnk your DIV_ROUND_UP() eliminate for the loop
> > >> in swap_buffer() is valid.  The whole point is that the current
> > >> code handles buffers which have a length which is not a multiple
> > >> of 4 properly, after your change it will no longer do so.
> > >>
> > > Do you really think so?
> > 
> > Yes, because you're rounding down so you'll miss the final
> > partial word (if any).
> >
> Nope. DIV_ROUND_UP() would give '1' as upper bound for lengths from 1 to
> 4, '2' for lengths from 5 to 8 and so on.
> 
> The loop with increment 4 and i < len does exactly the same.
> Try it for yourself, if you don't believe it.
> 
> 
Do you still think, the loop without DIV_ROUND_UP() is incorrect,
or can this patch be applied?


Lothar Waßmann
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