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Re: [PATCH] MII bus API for PHY devices

To: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] MII bus API for PHY devices
From: Andy Fleming <afleming@xxxxxxxxxxxxx>
Date: Fri, 19 Nov 2004 15:18:44 -0600
Cc: <netdev@xxxxxxxxxxx>, Linux Kernel list <linux-kernel@xxxxxxxxxxxxxxx>, <jason.mcmullan@xxxxxxxxxxx>, Andy Fleming <AFLEMING@xxxxxxxxxxxx>
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On Nov 18, 2004, at 17:26, Benjamin Herrenschmidt wrote:

On Thu, 2004-11-18 at 11:52 -0600, Andy Fleming wrote:

1) How should we pass initialization information from the system to the
bus.  Information like which irq to use for each PHY, and what the
address space for the bus's controls is.  I would like to enforce
encapsulation so that the ethernet drivers don't need to know this
information, or pass it to the bus.

Unfortunately, this is all quite platform specific and the ethernet
driver may be the only one to know what to do here... add to that
various special cases of the way the PHY is wired or controlled, I think
we can't completely avoid special casing...

Well, under the system I'm currently envisioning, the driver would be able to provide the data needed by the mii bus, but the hope would be to enable board files (for when the PHY is soldered on the motherboard, and the enet is not -- like on an MPC85xx) to provide this information instead, and leave out the enet as middleman.

2) How should we reflect the dependency of the ethernet driver on the
mii bus driver?

The ethernet driver can instanciate the PHYs at it's childs, though the
case of several MACs sharing PHYs will be difficult to represent...

I really don't want the driver to intantiate PHYs directly. The PHY is its own device, and the less net drivers have to understand their inner workings, the better. However, I hadn't considered the possibility of multiple MACs sharing the same PHY. It does, as you say, support my argument, though. With some careful design, the mii bus should be able to handle this type of setup easily.

One of my goals, personally, is to allow multiple net drivers to share the same mii bus, as in the case of the FCC enet controllers' PHYs on an 8560 ADS, which can be accessed through TSEC1's MII Management bus.

3) How should we bind ethernet drivers to PHY drivers?

I would have them instanciated by the ethernet driver. Besides, the PHY
driver will need to be able to identify it's "parent" driver in some
ways to deal with special cases. It would be nice to have a library of
utility code to independently deal with link tracking (basically what
drivers like sungem do independently), with a callback to the ethernet
driver to inform it of actual changes (notifier ?). MACs often have
autopoll features and PHY often have interrupts, but from experience,
that's not very useful and a good old timer based polling tend to do a
better job most of the time.

So when you say instantiated, would you consider calling an "attach" function with the phy_id and bus_id of the desired PHY instantiation? I'm fine with that. The PHY would need to be able to send notifications to the enet controller (currently done through a callback). I'm interested in ideas on how the notifier could be used (I have a distaste for callbacks).

Autopoll features sound pretty neat. I think the system should support that. PHY interrupts are supported (they work quite well on my 85xx system), as is timer-based polling. Do you really think that there are special cases which can't be handled using a library similar to the sungem_phy one?

Oh, and a 4th side-issue:
Should each PHY have its own file?  Or should we dump all the PHY
drivers in one file?  And if so, should THAT file be separate from the
mii bus implementation file?

I'd put all bcm5xxx in the same file ... they can be put together by

Yeah, that sounds good.

Andy Fleming
Open Source Team
Freescale Semiconductor, Inc

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