netdev - Re: [PATCH] Merge GT/MV642xx Support into MV643xx Driver [7/8]

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Message-ID: <20070720034043.GA28756@xyzzy.farnsworth.org>
Date:	Thu, 19 Jul 2007 20:40:43 -0700
From:	"Dale Farnsworth" <dale@...nsworth.org>
To:	"Steven J. Hill" <sjhill@...litydiluted.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Merge GT/MV642xx Support into MV643xx Driver [7/8]

On Thu, Jul 19, 2007 at 09:10:26PM -0500, Steven J. Hill wrote:
> Dale Farnsworth wrote:
> > 
> > You have replaced the use of the global PHY spinlock with a per-port spinlock.
> > However, the SMI register is shared by all ports.  The global lock is
> > needed to prevent simultaneous updates of the register by drivers for
> > multiple ports.
> > 
> > NAK
> >
> Are you sure? Notice that a majority of the spinlocks were changed to disable
> IRQs. Secondly, the lowest level mv_read/mv_write functions have to acquire
> the big mv64x60_lock before they can read or write registers. I see the PHY
> spinlock as being an additional and unnecessary lock to contend with. Am I
> make an improper assumption?

I'm sure.  (Of course, I could be wrong.)  On an SMP (or fully
preemptive) system, disabling IRQs doesn't provide sufficient
protection.  Nor does a per-port spinlock, since multiple ports
share the single register.  It seems to me that a driver-scope
lock is required.

-Dale
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