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

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Date:	Tue, 31 Mar 2009 18:58:33 +0800
From:	Li Yang <leoli@...escale.com>
To:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
Cc:	Scott Wood <scottwood@...escale.com>, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] ucc_geth: Rework the TX logic.

On Tue, Mar 31, 2009 at 5:07 PM, Joakim Tjernlund
<Joakim.Tjernlund@...nsmode.se> wrote:
> Scott Wood <scottwood@...escale.com> wrote on 30/03/2009 21:32:23:
>>
>> Joakim Tjernlund wrote:
>> >> different since descriptors are in MURAM which is ioremap()ed --
> though
>> >> switching to a cacheable mapping with barriers should be a
> performance
>> >> improvement.
>> >
>> > I always thought that MURAM was very fast. The whole reason to have
> BDs in
>> > MURAM is that it is faster than normal RAM, at least that is what I
>> > thought.
>>
>> Yeah, on second thought it probably wouldn't be worth it.  There's also
>> the question of under what circumstances the QE's MURAM accesses will be
>
>> cache-coherent.
>
> I am a bit confused, what isn't worth it? Currently MURAM isn't used by
> ucc_geth, but
> it is easy to change. Swap MEM_PART_SYSTEM to MEM_PART_MURAM, however,
> just
> tried that and the driver stopped working. I known this worked earlier
> because
> I tried it and I even think I sent a patch to Leo.
>
> What choices do we have, I see three:
>
> 1) MEM_PART_SYSTEM, as today.
> 2) MEM_PART_MURAM. I guess this should be uncacheable memory?
> 3) as gianfar, dma_alloc_coherent(). I presume this is uncacheable memory?
>

1 and 3 are the same.  All of them use cacheable memory as we have a
hardware coherency module to take care of the cache coherency problem.
 However it might be better to use dma_alloc_coherent() for the code
to be more readible.  Thanks.

- Leo
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