[U-Boot] [PATCH 1/2] mx6cuboxi: Fix Ethernet PHY detection problem

[Nikolay Dimitrov]

Hi Fabio,

On 05/04/2015 06:30 AM, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam at freescale.com>
>
> mx6cuboxi sometimes fails to recognize the Ethernet PHY:
>
> Net:   Phy 0 not found
>
> The explanation comes from a patch from Rabeeh:
>
> "The LED_ACT pin on the carrier-one boards had a pull down that
> forces the phy address to 0x0; where on CuBox-i and the production
> HummingBoard that pin is connected directly to LED that depending on
> the pull down strength of the LED it might be sampled as '0' or '1'
> thus the phy address might appear as either address 0x0 or 0x4."

There's no such thing as "LED pull-down". The forward voltage drop of a
LED is between 1.65V (red low-power LEDs) to 2.1V (green LEDs) to even
more for blue LEDs. Even the lowest Vf doesn't qualify as logic "0" for
LVCMOS33, which is around 1V max (Vil). The LED just can't pull-down the
voltage level low enough.

So, unless you have some control over the pin (via a programmable
on-chip pull-up or pull-down) which I doubt as it's a PHY pin, the
actual behavior is that the pin is floating, and samples a random value
at boot. Which means, the hardware is just buggy.

Kind regards,
Nikolay