netdev - RE: [PATCH] ucc_geth.c, make PHY device optional.

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Message-Id: <1183539047.20673.216.camel@gentoo-jocke.transmode.se>
Date:	Wed, 04 Jul 2007 10:50:46 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Li Yang-r58472 <LeoLi@...escale.com>
Cc:	linuxppc-dev Development <linuxppc-dev@...abs.org>,
	Netdev <netdev@...r.kernel.org>,
	Fleming Andy-afleming <afleming@...escale.com>
Subject: RE: [PATCH] ucc_geth.c, make PHY device optional.

On Tue, 2007-07-03 at 19:38 +0800, Li Yang-r58472 wrote:
> > -----Original Message-----
> > From: Joakim Tjernlund [mailto:joakim.tjernlund@...nsmode.se]
> > Sent: Tuesday, July 03, 2007 7:20 PM
> > To: Li Yang-r58472
> > Cc: linuxppc-dev Development; Netdev; Fleming Andy-afleming
> > Subject: RE: [PATCH] ucc_geth.c, make PHY device optional.
> > 
> > On Tue, 2007-07-03 at 16:22 +0800, Li Yang-r58472 wrote:
> > > > -----Original Message-----
> > > > From: Joakim Tjernlund [mailto:joakim.tjernlund@...nsmode.se]
> > > > Sent: Tuesday, July 03, 2007 3:21 PM
> > > > To: Li Yang-r58472
> > > > Cc: linuxppc-dev Development; Netdev; Fleming Andy-afleming
> > > > Subject: RE: [PATCH] ucc_geth.c, make PHY device optional.
> > > >
> > > > On Tue, 2007-07-03 at 11:42 +0800, Li Yang-r58472 wrote:
> > > > > > -----Original Message-----
> > > > > > From: netdev-owner@...r.kernel.org
> > > > > [mailto:netdev-owner@...r.kernel.org] On
> > > > > > Behalf Of Joakim Tjernlund
> > > > > > Sent: Tuesday, July 03, 2007 8:52 AM
> > > > > > To: 'linuxppc-dev Development'; 'Netdev'; Li Yang-r58472
> > > > > > Subject: [PATCH] ucc_geth.c, make PHY device optional.
> > > > > >
> > > > > > > This patch makes the PHY optional for ucc_geth.c ethernet
> > > driver.
> > > > > > > This is useful to support a direct mii to mii connection to,
> for
> > > > > example,
> > > > > > > a onboard swicth.
> > > > > > >
> > > > > > > Signed-off-by: Joakim Tjernlund
> <joakim.tjernlund@...nsmode.se>
> > > > > > ----
> > > > > Hi Joakim,
> > > > >
> > > > > I'm wondering if we really need to have the option to disable
> > > phylib.
> > > >
> > > > maybe, but it has to be dynamic too. I need to use PHY on UCC2 and
> mii
> > > > on UCC3 and UCC4.
> > > >
> > > > > Actually we have made phylib selected by default for ucc_geth.
> Many
> > > L2
> > > > > switch chips have the capacity to be controlled.  Therefore they
> can
> > > be
> > > > > managed as a phy device.
> > > >
> > > > Yes, they can be but why force a PHY impl. when its is of no use?
> The
> > > > only thing the eth driver needs from the it is speed and duplex.
> If
> > > > these are fixed, you don't need to talk with a PHY.
> > >
> > > The driver needs to get and set the link speed/status on runtime
> (such
> > > as for ethtool interface).  Currently this is implementation through
> > > phydev interface.  IMHO, it will be easier to maintain if we only
> use
> > > this standard interface, rather than use different interfaces for
> > > different cases.
> > 
> > hmm maybe, but there is no need to much around with speed/status
> > from user space. The speed and duplex must be set before user space
> > is up.
> > 
> > >
> > > >
> > > > > For the MII interface which is not
> > > > > configurable, shouldn't we use the fixed phy support from
> Vitaly?
> > > >
> > > > Well, I think the the fixed phy is great when your eth driver
> requires
> > > a
> > > > PHY, but it is a workaround with extra processing overhead. IMHO
> the
> > > > best impl. is to make the PHY optional in the eth driver and as
> you
> > > can
> > > > see from the patch, that was really simple.
> > >
> > > I agree there is overhead. However, it will have the advantage of
> > > abstracting all the PHY related stuff out of controller driver.
> > >
> > > >
> > > > An useful extension would be to add a new propety in the DTS to
> hold
> > > > initial speed and duplex(perhaps extend phy-connection-type). This
> > > > would be useful for the fixed driver too as one could derive speed
> and
> > > > duplex for the fixed phy from that property instead of creating a
> > > fixed
> > > > phy for each speed and duplex one want to support.
> > >
> > > I agree that there should be a device node to configure it.  The
> current
> > > fixed phy driver is a little bit too complex to emulate the register
> > > access.  Maybe it's better to have a null phy driver which just
> reads
> > > PHY capacity and status from device node.
> > 
> > A null phy driver is better than the current fixed phy, I agree.
> > Where would you like to put initial speed and duplex? In a fake phy
> node
> > or in the ethernet node?
> 
> I think a fake phy node is better.
> 
> - Leo

OK, but then a new property in PHY node is needed which holds
the initial speed and duplex. 
initial-phy-capacity = <speed duplex> ?
This should be useful for real PHYs too if, for instance, autoneg isn't
working/supported/wanted.

Maybe it should be:
initial-phy-capacity = <speed duplex autoneg> 
or
initial-phy-capability = <speed duplex autoneg> 

 Jocke
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