Broken ethernet on SolidRun cubox-i

[Michael Walle]

Am 2020-12-27 16:33, schrieb Michael Walle:
> Am 2020-12-26 13:34, schrieb Russell King - ARM Linux admin:
>> I'd forgotten that there were boards out there with this problem...
>> the PHY address configuration is done via the LED_ACT pin, and 
>> SolidRun
>> omitted a pull resistor on it, so it "floats" with the leakage current
>> of the LED/pin - resulting in it sometimes appearing at address 0 and
>> sometimes at address 4.
> 
> Mh, I've guessed that too, but there must be more to it. The datasheet
> says it has an internal weak pull-up. Or Atheros messed up and it 
> doesn't
> reliably work if there is actually an LED attached to it. But then, why
> would any other stronger pull-up/down work..

Mhh, nevermind, from the commit log [1].

   "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."

So it actually depends on the forward voltage of the LED and the
hi/low thresholds of the AT8035.. nice! Oh and btw. this pin also
switches between high and low-active LED output. So the missing
pull-down might not only switch the PHY address to 4 but also invert
the LED state.

-michael

[1] 
https://github.com/SolidRun/u-boot/commit/712be3eef69a2b0205d3b87fb5ab5632e36722d7