netdev - Re: [PATCH 03/12] fs_enet: Add FEC TX Alignment workaround for MPC5121.

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Date:	Wed, 6 May 2009 16:42:55 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Wolfgang Denk <wd@...x.de>
Cc:	linuxppc-dev@...abs.org, John Rigby <jrigby@...escale.com>,
	Piotr Ziecik <kosmo@...ihalf.com>, netdev@...r.kernel.org,
	John Rigby <jcrigby@...il.com>, Detlev Zundel <dzu@...x.de>
Subject: Re: [PATCH 03/12] fs_enet: Add FEC TX Alignment workaround for 
	MPC5121.

On Wed, May 6, 2009 at 4:12 PM, Wolfgang Denk <wd@...x.de> wrote:
> Dear Grant Likely,
>
> In message <fa686aa40905061337w6aa82f5aj787618ba108e528f@...l.gmail.com> you wrote:
>>
>> > The FEC on 5121 has problems with misaligned tx buffers.
>> > The RM says any alignment is ok but empirical results
>> > show that packet buffers ending in 0x1E will sometimes
>> > hang the FEC. Other bad alignment does not hang but will
>> > cause silent TX failures resulting in about a 1% packet
>> > loss as tested by ping -f from a remote host.
>> >
>> > This patch is a work around that copies every tx packet
>> > to an aligned skb before sending.
>>
>> OUCH!
>
> Yes :-(
>
>> > +#else
>> > +#define tx_skb_align_workaround(dev, skb) (skb)
>> > +#endif
>>
>> Another use of #ifdef blocks.  What is the multiplatform impact?
>
> Hm... Can you recommend a better way to solve the problem? Suggestions
> are welcome.

I'd rather see a runtime selectable workaround.  ie. enable it based
on the compatible property.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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