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

[Fabio Estevam]

Hi Nikolay,

On Mon, May 4, 2015 at 1:18 AM, Nikolay Dimitrov <picmaster at mail.bg> 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.
>
> 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.

As mentioned in the commit log this explanation comes from Solid-run.

The key point here is that the PHY can appear at 0x0 and 0x4, so this
patch handles such case.

Regards,

Fabio Estevam