Phy layer notes (was Re: [RFR] gianfar ethernet driver)

David Woodhouse wrote:

Hmmm. 

eth0: Running with NAPI disabled
eth0: 64/64 RX/TX BD ring size
eth1: Gianfar Ethernet Controller Version 1.0, 05:e6:9e:c0:05:e6
eth1: Running with NAPI disabled
eth1: 64/64 RX/TX BD ring size      
eth0: PHY id 2060e1 is not supported!
eth0: No PHY found
IP-Config: Failed to open eth0
IP-Config: Device `eth0' not found

The PHY is a BCM5421S. Does it really have to give up completely? Isn't
there a subset of common MII support it could use?

Is it expected that every NIC driver will include its own version of
support for the PHYs which have actually been seen paired with that NIC,
or is there some more generic support planned?

David W and I discussed some of this on IRC.

1) most gige phys can be treated with generic GMII code.  unfortunately 
experience shows that phy init can often involve phy-specific magic 
sequences.

2) we do need a generic phy layer, and I'm looking for volunteers who 
want to prototype a nice, small, compact one.  BenH has a nice template 
in sungem_phy.c.

3) drivers/net/mii.c and include/linux/mii.h need GMII code and 
constants.  Feel free to add.

4) generic TBI code would be nice, too.  (TBI is a standard gige fibre 
interface)

5) sometimes a MAC+phy pairing is unique enough that you need 
MAC-specific support for a particular phy.  For example, one might wind 
up with two phy drivers, one a generic Broadcom GMII phy driver (for use 
by any NIC driver), and one a tg3-specific Broadcom GMII phy driver.