netdev - Re: [PATCH 2/2] ucc_geth: Rework the TX logic.

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Date:	Thu, 26 Mar 2009 19:20:49 +0100
From:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
To:	avorontsov@...mvista.com
Cc:	leoli@...escale.com, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] ucc_geth: Rework the TX logic.

Anton Vorontsov <avorontsov@...mvista.com> wrote on 26/03/2009 19:05:43:

> On Thu, Mar 26, 2009 at 05:43:25PM +0100, Joakim Tjernlund wrote:
> [...]
> > > bd == ugeth->confBd[txQ]
> > > and
> > > !in_be32((u32 __iomem *)(bd+4))
> > > 
> > > Are not equivalent wrt. speed. MMIO accessors should be rather
> > > slow comparing to normal memory.
> > 
> > Yes, I know. I did it this way because I something broke under stress
> > when ugeth->confBd[txQ] instead. The ucc_geth_tx() and 
> > ucc_geth_start_xmit()
> > gets out of sync somehow.
> 
> Would be great if you could investigate it more. Maybe there is
> a serious bug somewhere, or maybe you're introducing another
> (yet hidden) bug...

I have spent some time on it and didn't see how to do it. I don't think
the current method hides any bugs. I have used this method on 8xx for
many years and it works well.

Actually the current method might work without the 
spin_lock_irq(&ugeth->lock)/spin_unlock_irq(&ugeth->lock)
in ucc_geth_start_xmit(). I can't break it, can you?

 Jocke
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