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

[Nikolay Dimitrov]

Hi Rabeeh,

On 05/04/2015 03:35 PM, Rabeeh Khoury wrote:
> On 05/04/2015 07:18 AM, Nikolay Dimitrov wrote:
>> 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.
> This is AR8035 implementation; in reset stage the LED pin is
> configured as input, and pull up/down does matter. In this case it
> configures the PHY address.
>
> After reset is deasserted the same LED pin becomes output and then
> according to the previous pull/up it should be active high/low (i.e.
>  driver or sink).

I know this. This is why I said that the pin is floating and the R+LED
can't define a proper logic level during configuration bootstrapping. In
such situations there should be an external pull-up/pull-down to make
sure things work properly.

Regards,
Nikolay