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

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Message-Id: <1183461586.20673.192.camel@gentoo-jocke.transmode.se>
Date:	Tue, 03 Jul 2007 13:19:46 +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 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?
Perhaps this should live in BSP code instead?

 Jocke
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