netdev - Re: Porting the ibm_newemac driver to use phylib (and other PHY/MAC questions)

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Date:	Sun, 3 May 2009 00:26:05 -0400
From:	Kyle Moffett <kyle@...fetthome.net>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Josh Boyer <jwboyer@...ux.vnet.ibm.com>,
	netdev <netdev@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org
Subject: Re: Porting the ibm_newemac driver to use phylib (and other PHY/MAC 
	questions)

On Thu, Apr 30, 2009 at 6:21 PM, Kyle Moffett <kyle@...fetthome.net> wrote:
>>> I'm also curious about the intent of the "mdio_instance" pointer (IE:
>>> the "mdio-device" property).  Is that used when all the PHY devices
>>> are attached to the MDIO bus of only one of the (multiple) emac
>>> devices?
>>
>> It's common especially on older SoCs using EMAC to have only one of
>> the EMAC instance with an MDIO bus for configuring the PHYs. This is one
>> of the reasons why I have the mutex in the low level MDIO access
>> routines since 2 EMACs can try to talk to the same MDIO, and this is the
>> problem I had with phylib back then which was doing everything in atomic
>> contexts.
>
> Ok, good, the current mdiobus code seems to make handling this a good
> deal easier.

Ok, I've dug through the docs on the 460EPx (the CPU I'm using), and
I'd like some confirmation of the following:

*  The EMAC hardware itself internally has its own dedicated
MDIO/MDClk lines, driven by the STACR register.

*  On many/most cpus, there is only a single set of external
MDIO/MDClk pins, driven either off the ZMII bridge or the RGMII
bridge.

*  Both bridge-types have their own internal register for switching
the external MDIO/MDClk pins between the two sets of internal
EMAC<=>bridge links.

*  Some SoCs have both an ZMII and an RGMII bridge, and the external
MDIO/MDClk pins are only connected to one of the two bridges (How do I
know which one?  Alternatively, do I just program both and hope for
the best?).

*  Some older SoCs simply export the MDIO/MDClk pins from one of their
internal EMAC chips and don't bother with running it through the
multiplexing bridge.

Are there any SoCs which actually export the MDIO/MDClk pins from
both/all of their EMACs?

Cheers,
Kyle Moffett
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