netdev - Re: [PATCHv3 1/4] net: phy: decouple PHY id and PHY address in fixed PHY driver

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Date:	Sat, 08 Mar 2014 04:09:23 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Florian Fainelli <f.fainelli@...il.com>
Cc:	Lior Amsalem <alior@...vell.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Christian Gmeiner <christian.gmeiner@...il.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Mark Rutland <mark.rutland@....com>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv3 1/4] net: phy: decouple PHY id and PHY address in fixed PHY driver

On Tue, 4 Mar 2014 20:04:24 +0100, Thomas Petazzoni <thomas.petazzoni@...e-electrons.com> wrote:
> Dear Florian Fainelli,
> 
> On Tue, 4 Mar 2014 10:43:12 -0800, Florian Fainelli wrote:
> 
> > >  struct fixed_phy {
> > > -       int id;
> > > +       int addr;
> > >         u16 regs[MII_REGS_NUM];
> > >         struct phy_device *phydev;
> > >         struct fixed_phy_status status;
> > > @@ -104,8 +104,8 @@ static int fixed_phy_update_regs(struct fixed_phy *fp)
> > >         if (fp->status.asym_pause)
> > >                 lpa |= LPA_PAUSE_ASYM;
> > >
> > > -       fp->regs[MII_PHYSID1] = fp->id >> 16;
> > > -       fp->regs[MII_PHYSID2] = fp->id;
> > > +       fp->regs[MII_PHYSID1] = 0xdead;
> > > +       fp->regs[MII_PHYSID2] = 0xbeef;
> > 
> > I am still scratching my head as to whether we want that change to be
> > in this particular version of changes, or if we want that to happen at
> > a later time when (if?) we can finally get some proper OUI number
> > allocation.
> > 
> > Technically we are presenting some sort of ABI to user-space, although
> > detecting a fixed PHY device by reading its MII_PHYSID1/2 and matching
> > it against its PHY address on the fixed MDIO bus would have been a
> > little "weak" (especially when you can check that the parent device in
> > sysfs is the fixed-0 bus).
> 
> Well the problem is that fp->id really isn't an id, it's the fake
> address of the PHY on the fake fixed MDIO bus. So it would mean that
> the MII_PHYSID of the first fixed PHY would probably be 0x0, then the
> second would have 0x1, then 0x2, and so on.

I think the change is reasonable, but I'm not thrilled with the 0xdeadbeaf
constant. I'd rather PHYSID simply be left as 0.

g.
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