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Date: 3 Apr 2006 14:44:30 -0000
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From: "Dale Farnsworth" <dale@farnsworth.org>
To: TSchnuerer@men.de, linuxppc-dev@ozlabs.org
Subject: Re: MPC5200 FEC Ethernet only halfduplex ?
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TSchnuerer@men.de wrote:
> Im working with Linux on our MPC5200 Board, with the latest Rev. B3 
> Processor.
> I was updating our Linux BSP from BestComm 2.1 to 2.2 some time ago and
> used your patches which increased usability of the FEC very much.
> 
> There is a line in the driver code which I dont understand, it says:
> + fec_restart(dev, 0); /* always use half duplex mode only */
> 
> Why can only half duplex be used ?

The reason is simple, but not satisfying.  The driver has no
mechanism to detect PHY status changes and thus no way to determine
when a connection changes from full to half duplex.  It needs a
poll function for PHY status change.  Doing only half-duplex
avoids this issue--at a big performance cost.

I think a poll function was added in the Denx version.

The MPC5200 FEC driver desperately needs a rewrite.

-Dale