[PATCH] ARM: dts: am335x-bone-common: Increase MDIO reset deassert delay to 50ms

[Kevin Hilman]

Roger Quadros <rogerq at kernel.org> writes:

> On 31/10/2024 11:29, Geert Uytterhoeven wrote:
>> Commit b9bf5612610aa7e3 ("ARM: dts: am335x-bone-common: Increase MDIO
>> reset deassert time") already increased the MDIO reset deassert delay
>> from 6.5 to 13 ms, but this may still cause Ethernet PHY probe failures:
>> 
>>     SMSC LAN8710/LAN8720 4a101000.mdio:00: probe with driver SMSC LAN8710/LAN8720 failed with error -5
>> 
>> On BeagleBone Black Rev. C3, ETH_RESETn is controlled by an open-drain
>> AND gate.  It is pulled high by a 10K resistor, and has a 4.7µF
>> capacitor to ground, giving an RC time constant of 47ms.  As it takes
>> 0.7RC to charge the capacitor above the threshold voltage of a CMOS
>> input (VDD/2), the delay should be at least 33ms.  Considering the
>> typical tolerance of 20% on capacitors, 40ms would be safer.  Add an
>> additional safety margin and settle for 50ms.
>> 
>> Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
>
> Reviewed-by: Roger Quadros <rogerq at kernel.org>

Reviewed-by: Kevin Hilman <khilman at baylibre.com>
Tested-by: Kevin Hilman <khilman at baylibre.com>