[U-Boot-Users] [PATCH] Add support for Generic PHY in macb

[Michael Schwingen]

Haavard Skinnemoen wrote:
> Right. We might need to add support for such PHYs, but just disabling
> the sanity check is far from enough.
>   
Agreed - in the case of a single MII-connected TP PHY, we really need 
working MDIO (or some replacement). For special cases (100BaseF fiber, 
which is always fixed speed and duplex), some equivalent to Linux' fixed 
phy handling would be needed.

>> The chip may do autonegotiation by default, however, the MAC driver 
>> still needs to know about the negotiated speed/duplex, so unless there 
>> is some board-specific way to read those (eg. by GPIO pins), only one 
>> speed/duplex will work and all other modes will be broken. This is 
>> different from the case with the hardwired ethernet switch - in case of 
>> the switch, we know that the MII port is always running at 100Mbps, 
>> full-duplex.
>>     
>
> Hmm...most switches support autonegotiation don't they? If not, what
> happens if you plug in in an old computer with a 10Mbps ethernet board?
>   
The switches support autonegotiation on the TP ports. The internal MII 
port which connects them to the CPU/MAC is usually run at fixed 100Mbps 
full-duplex.

If the switch has MDIO, you can quary the status of the external PHYs - 
however, from the point of the MAC driver, that is useless, you need to 
assume that the MII link is always up, since there is no autonegotiation 
on the MII bus.

Older switches (I have worked with the Marvell M88E6050) do not even 
have MDIO - the MII runs fixed, and the TP ports can either 
autonegotiate, or can be set to fixed 10/100/halfduplex operation using 
strapping pins.

cu
Michael