linux-kernel - Re: [PATCH v2] net: macb: do not scan PHYs manually

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Date:	Thu, 28 Apr 2016 10:55:56 -0500
From:	Nathan Sullivan <nathan.sullivan@...com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Florian Fainelli <f.fainelli@...il.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: Re: [PATCH v2] net: macb: do not scan PHYs manually

On Thu, Apr 28, 2016 at 05:44:14PM +0200, Nicolas Ferre wrote:
> Le 28/04/2016 16:46, Nathan Sullivan a écrit :
> > Since of_mdiobus_register and mdiobus_register will scan automatically,
> > do not manually scan for PHY devices in the macb ethernet driver. Doing
> > so will result in many nonexistent PHYs on the MDIO bus if the MDIO
> > lines are floating or grounded, such as when they are not used.
> > 
> > Signed-off-by: Nathan Sullivan <nathan.sullivan@...com>
> 
> Well, as explained in the commit message that added this feature and in
> the comment, if no phy is specified in the DT we end up without phy...
> 
> There are AT91 platforms which lack specification for the phy node in
> the DT. So, I don't know if there is a better way to deal with this case
> but I see this removal as risky.
> 
> Bye,
> 
> Nicolas Ferre

Hmm, are AT91 platforms special in this regard? As far as I can tell, this
driver (macb) and Marvell PXA are the only ethernet drivers that call
mdiobus_scan directly, and PXA does it on a known address. I do see that there
are trees that use macb and don't have a phy listed, which is unfortunate.

Another way to fix our issue would be to consider all 0x0s a bad ID in
mdiobus_scan, so grounded MDIO lines do not get PHYs scanned.  Or we could add a
DT property to disable the manual scan.  I'm not sure what the correct solution
is, do you have a preference?