[DEBUG] rk3399-nanopi-neo4: SPL SD init may report -5 due to SD power-on timing

[Sune Brian]

> Is your issue specific to a reboot or cold boot?

First got to think in logical flow. As the SD card fail to pass the
detection of valid SD card aka -5 error then it is 100% impossible
to enter U-Boot user control phase, same as kernel nor distro.
Hence, also cannot do 'reset' on U-Boot nor 'sudo reboot' on distro.

So the answer is cold boot.
However, do reboot also have issue? This is not tested yet as
we got to solve the regulator behavior trouble first.

> Try adding something like following to rk3399-nanopi-neo4-u-boot.dtsi
> to add a 2ms delay to ensure the voltage for the vcc3v0_sd regulator is
> stabilized when it is enabled. Or any other timing that is required.
>
> &vcc3v0_sd {
>         startup-delay-us = <2000>;
> };

So far i got to comment this in the dts in order to boot.

&sdmmc {
// vmmc-supply = <&vcc3v0_sd>;
};

> I only have a NanoPi M4B from the nanopi4 family to run tests on.

My board is nanopi neo4. If my reading is correct.
The schematic on your board is mostly same as the neo4 on SD card.

M4B page 19 [1], NEO4 page 18 [2]

Should able to check if issue can be reproduced. The LDO itself could be
slow as this is not digital based LDO, it is old analog control-loop
one I guess.
Meantime, the RK3399 may not have internal ADC or HW to sense the rail sanity.

Brian

[1] https://wiki.friendlyelec.com/wiki/images/1/16/NanoPi-M4B-1909-Schematic.pdf
[2] https://wiki.friendlyelec.com/wiki/images/b/bb/NanoPi_NEO4_2008_SCH.pdf