Subject: Re: [PATCH 1/4 v2] powerpc: document max-speed and interface-type properties

From: Segher Boessenkool <[email-masked]>
Date: Tue, 17 Apr 2007 12:25:51 +0200

>> You can put "rgmii" or whatever in the "compatible" property
>> as well.
>>
> I don't understand how intermixing PHY device compatibility with the
> UCC connection to the PHY would be a good thing.

"compatible" means "what kind of device is this", for the
purposes of a client program (i.e., Linux) matching a
driver to it (i.e., it should say what kind of PHY it
is, and phylib should use that info -- in most cases,
it won't need more than the least specific entry in
"compatible", i.e. "rgmii" or whatever.

>>> If I were to put the properties in the PHY node, I wouldn't be able 
>>> to
>>> describe a 1000Mbit/s capable UCC connected to a 100Mbit/s capable 
>>> PHY,
>>> or vice versa.
>>
>> Of course you can.  The "compatible" in the enet node
>> implies it can do 1000Mbps; the "compatible" in the
>> PHY node implies it does 100Mbps.
>
> compatible in the UCC node is currently set to "ucc_geth", which does
> not necessarily imply that that UCC can do 1000Mbit/s.  Some UCCs can
> only do 100Mbit/s.

So those UCCs should have a different "compatible" entry.
It's not rocket science.

> We currently do not have hardware that connects UCC with max-speed x
> with a PHY with max. speed capability of y, where x != y, so there is
> currently no need to specify the speed of the PHY.  Not that that would
> be needed; the phylib would call ucc_geth's adjust_link with the new
> speed.  Note that the max-speed property is used to set registers in 
> the
> UCC only.

max-speed of connection = min(max-speed of enet, max-speed
of PHY) -- and both of those are implied by their respective
"compatible" properties.

Segher