Problem in phy.c, when using fixed network speed

Problem in phy.c, when using fixed network speed

[Michael Koch]

Hi all,
during testing i encountered a problem with setting up a 5200B 
controller with a MICREL phy at static 100MBit full duplex - without 
autonegotiation.

I performed this as usual with ethtool and was succesful when i had my 
link partner up, providing a link.

When kepping the link partner off, meaning no link at all, my machine 
started to degrade its link capabilities ending 10MBit half duplex.

I tracked it down to drivers/net/phy/phy.c:
in the function phy_state_machine, the case block PHY_FORCING causes 
this (at least for me) undesired behaviour. Calling the 
phy_force_reduction function degrades actually an intentionally static 
setup.

I deactivated those lines, and it works for me.

But anyhow i feel soe need to have a general solution that takes static 
non autonagotiation setups into account.

What do you think?

Hope to hear from you

Michael

RE: Problem in phy.c, when using fixed network speed

[Jenkins, Clive]

> Hi all,
> during testing i encountered a problem with setting
> up a 5200B controller with a MICREL phy at static
> 100MBit full duplex - without autonegotiation.
>
> I performed this as usual with ethtool and was
> succesful when i had my link partner up, providing
> a link.
>
> When kepping the link partner off, meaning no link
> at all, my machine started to degrade its link
> capabilities ending 10MBit half duplex.
>
> I tracked it down to drivers/net/phy/phy.c:
> in the function phy_state_machine, the case block
> PHY_FORCING causes this (at least for me) undesired
> behaviour. Calling the phy_force_reduction function
> degrades actually an intentionally static setup.
>
> I deactivated those lines, and it works for me.
>
> But anyhow i feel soe need to have a general
> solution that takes static non autonagotiation
> setups into account.
>
> What do you think?
>
> Hope to hear from you
>
> Michael

Yes, I have encountered this before. I think it dates=20
back to before Auto Negotiation became part of the=20
IEEE802* standard and each manufacturer implemented=20
its own strategy to establish a link. Although it is=20
possible "by experiment" to find the speed of your=20
link partner, it is impossible to determine its=20
Full/Half Duplex mode. IMHO when a fixed speed and=20
duplex setting is applied, phy.c should keep that=20
setting regardless of whether or not the link is=20
established. Not only is this undesirable behaviour,=20
but it deviates from the standard.

Clive