[U-Boot] [PATCH] revert "tsec: Force TBI PHY to 1000Mbps fullduplex in SGMII mode"

[Peter Tyser]

On Fri, 2010-11-19 at 13:53 +0800, Li Yang wrote:
> ><snip>
> >
> >> >My understanding is that the SGMII link is always at 1000Mbps speed -
> >> >see figure 1 from the app note.  Additionally look at figure 3.  My
> >> >understand from it, and the app note's text is that SGMII
> >> >auto-negotiation doesn't really occur - its just passing the PHY-side
> >> >auto-negotiation results to the Freescale MAC, which software then
> >> >configures.  I'm not sure what the purpose of the "SGMII
> >> >auto-negotiation" is - its not really auto- negotiating and the same
> >> >information can be read from the PHY via its MDIO interface, which is
> >what is happening on X-ES boards currently.
> >>
> >> I guess the point is to save MDIO signals to the external PHY and read
> >> the negotiated result from the internal TBI PHY.
> >
> >Do the P2020DS, MPC8572DS and P1/P2 RDB boards not have an MDIO interface
> >to their PHYs'?  I've never heard of a board that doesn't, and would guess
> >the tsec driver in U-Boot requires a PHY to be accessible via MDIO to use
> >the corresponding network interface.
> 
> I'm not sure which specific silicon omits the MDIO signal.  But quoting from
> the app note you mentioned:
> 
> " Depending on the PowerQUICC part used, some eTSEC’s may or may not
> provide an external
> MDIO management interface. However, the TBI block for each eTSEC is
> associated in a one to one
> manner, even if that eTSEC does not have an external MDIO connection."

I believe some parts don't have an external MDIO interface for every
eTSEC.  if my memory is correct the MPC8572 only has 2 MDIO ports and 3
eTSECS.  But 1 MDIO port can be used to communicate with all 3 eTSECS'
PHYs assuming each PHY has a unique address.  (eg eTSEC1, 2, and 3 use
eTSEC1's MDIO port).

> The auto-negotiation mechanism between TBI PHY and real PHY does make
> it possible
> to save external MDIO signals if only SGMII interface is used.

That seems like an awfully big sacrifice to save routing 2 signals.
I've never heard of anyone doing this.  I don't think the current tsec
driver in U-Boot would support this configuration either, so I'm not
sure how much weight it holds.

> >I can forward you the email thread about SGMII auto-negotiation with
> >Freescale's FAE off-list if you'd like as well.
> 
> Yes, please.  Thanks

I just forwarded it.

Best,
Peter