netdev - Re: [PATCH] e1000e: workaround missing power down mii control bit on 82571

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Date:	Thu, 16 Dec 2010 14:14:21 -0800
From:	Arthur Jones <arthur.jones@...erbed.com>
To:	"Allan, Bruce W" <bruce.w.allan@...el.com>
CC:	Ben Hutchings <bhutchings@...arflare.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] e1000e: workaround missing power down mii control bit
 on 82571

Hi Bruce, ...

On Thu, Dec 16, 2010 at 12:04:26PM -0800, Arthur Jones wrote:
> Hi Bruce, ...
> 
> On Thu, Dec 16, 2010 at 11:28:18AM -0800, Allan, Bruce W wrote:
> > >-----Original Message-----
> > >From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
> > >Behalf Of Allan, Bruce W
> > >Sent: Thursday, December 16, 2010 11:04 AM
> > >To: Ben Hutchings; Arthur Jones
> > >Cc: Kirsher, Jeffrey T; netdev@...r.kernel.org
> > >Subject: RE: [PATCH] e1000e: workaround missing power down mii control bit on
> > >82571
> > >
> > >>-----Original Message-----
> > >>From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
> > >>Behalf Of Ben Hutchings
> > >>Sent: Thursday, December 16, 2010 10:57 AM
> > >>To: Arthur Jones
> > >>Cc: Kirsher, Jeffrey T; netdev@...r.kernel.org
> > >>Subject: Re: [PATCH] e1000e: workaround missing power down mii control bit on
> > >>82571
> > >>
> > >>Adding this special case into MDIO access seems like a really nasty
> > >>hack.  Surely the callers that set the control register should take care
> > >>of this.
> > >>
> > >>Ben.
> > >
> > >Agreed.  I am setting up to repro now to see if it is an actual hardware
> > >issue or just a software bug; either way, this patch is not the correct
> > >approach and I'll follow up shortly.
> > >
> > >Bruce.
> > 
> > It's the reset in e1000_set_settings() which ignores that we had previously
> > powered off the Phy.  I'll go through the rest of the code and fix up this
> > and any other occurrences of similar issues properly.
> 
> Thanks for having a look!
> 
> We do a read-modify-write there of
> the PHY control register.  We take
> the rest of the bits as being good,
> but, for some reason we don't get the
> power down bit (always reads back
> zero).  Is this a known 82571 issue?
> On 82574, e.g., we seem to get the
> power down bit back when we read...

BTW:  The 802.3 spec seems to indicate
that this bit _should_ be readable even
when the PHY is powered down (i.e.  this
is a PHY bug)...

Arthur

> 
> Are you sure you want to spread that
> 82571 specific logic all over the driver?
> 
> Arthur
> 
> > 
> > Thanks for reporting this issue Arthur.
> > 
> > Bruce.
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