netdev - Re: [PATCH] ucc_geth: Rework the TX logic.

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Date:	Mon, 30 Mar 2009 12:45:17 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
CC:	Li Yang <leoli@...escale.com>, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org, pku.leo@...il.com
Subject: Re: [PATCH] ucc_geth: Rework the TX logic.

Joakim Tjernlund wrote:
> Scott Wood <scottwood@...escale.com> wrote on 30/03/2009 19:22:03:
>> Joakim Tjernlund wrote:
>>> gianfar does not seem to use in_/out_ functions for the BDs. Works 
> just
>>> fine that too it seems.
>> It does now that it has explicit barriers in a few places.  Before they
> 
> In 2.6.29 or later?

No, it was earlier.

>> were added, it would sometimes fail under load.  That was due to a 
>> compiler reordering, but CPU reordering was possible as well.
> 
> Does not the CPU skip reordering if the guarded bit is set?

The guarded bit is typically not set for DMA buffers.  ucc_geth is a bit 
different since descriptors are in MURAM which is ioremap()ed -- though 
switching to a cacheable mapping with barriers should be a performance 
improvement.

-Scott
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