RE: i.MX28 based system losing eth0 on boot

[fugang.duan@xxxxxxxxxxxxx]

From: Brian Lilly <brian@xxxxxxxxxxxxxxxx>
Data: Thursday, May 08, 2014 3:52 AM

>To: Florian Fainelli
>Cc: Uwe Kleine-KÃnig; David S. Miller; Estevam Fabio-R49496; Jim Baxter; Li Frank-
>B20596; Duan Fugang-B38611; netdev; linux-kernel@xxxxxxxxxxxxxxx; kernel
>Subject: Re: i.MX28 based system losing eth0 on boot
>
>Florian:
>
>Thank you for your help.
>
>After doubling the timeout length it worked.
>
>I managed to get my hands on a imx28evk board and compared our component load
>versus theirs, to find they have a 1.5k pull-up on ENET_MDIO to +3.3v which wasn't
>present on our board.  Adding a 1.5k pull-up resistor on ENET_MDIO solves the
>problem, and boots as expected without patching anything.
>
>Sorry for the trouble on this.
>
>Apparently our EE had some question as to whether or not the pull-up was necessary,
>and put it in the schematic, and the footprint on the board, but marked it as a
>DNP, which of course left it off the board and out of the BOM.
[...]

Yes, 1.5K pull-up on MDIO is necessary, otherwise write/read phy register data is not right due to the drive strength is not enough.

Thanks,
Andy