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

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Date:	Fri, 31 Oct 2014 06:32:10 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, rmk+kernel@....linux.org.uk,
	Frank.Li@...escale.com, fabio.estevam@...escale.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: net: fec: fix regression on i.MX28 introduced by rx_copybreak
 support

Hi,

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.


Lothar Waßmann
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