netdev - Re: [PATCH] net: ibm_newemac: Don't start autonegotiation when disabled in BMCR (genmii)

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Date:	Tue, 19 Jul 2011 13:59:57 +0200
From:	Stefan Roese <sr@...x.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linuxppc-dev@...abs.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: ibm_newemac: Don't start autonegotiation when disabled in BMCR (genmii)

Hi Ben,

On Tuesday 19 July 2011 13:35:22 Benjamin Herrenschmidt wrote:
> On Tue, 2011-07-19 at 12:50 +0200, Stefan Roese wrote:
> > As noticed on a custom 440GX board using the Micrel KSZ8041 PHY in
> > fiber mode, a strapped fixed PHY configuration will currently restart
> > the autonegotiation. This patch checks the BMCR_ANENABLE bit and
> > skips this autonegotiation if its disabled.
> 
> Won't that just break aneg on everything else ?
> 
> IE, most other PHYs rely on ANENABLE being set further down this same
> function (especially if the FW doesn't do it but even then, we may reset
> PHYs along the way etc...)

If aneg is enabled for a PHY (e.g. not strapped to fixed configuration), I 
don't see how this patch will change the current aneg behaviour. Perhaps I'm 
missing something, but I tested this on some boards with aneg enabled (Sequoia 
etc). And I didn't notice any problems.
 
> This is something that really a case where the device-tree should
> indicate that aneg shall not be performed and from there don't call
> setup_aneg at all.

I feel that this BMCR_ANENABLE bit should be evaluated, but I have no strong 
preference here. If you prefer that this should be handled via a new dt 
property (phy-aneg = "disabled" ?), I can implement it this way. Just let me 
know.

Thanks,
Stefan
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