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

[Tom Rini]

On Fri, Oct 31, 2025 at 12:10:36PM +0800, Sune Brian wrote:

> Hello U-Boot maintainers,
> 
> While testing mainline U-Boot (v2026.01-rc1-00070-ge34d01d23e45) on the
> FriendlyARM NanoPi NEO4 (RK3399), I observed that SPL sometimes fails to
> initialize the SD card with the following message:
> 
>     spl: mmc init failed with error: -5
>     SPL: failed to boot from all boot devices
> 
> After investigation, the root cause appears to be related to the **SD card
> power rail (`vcc3v0_sd`) timing during SPL startup**. On the NanoPi NEO4,
> the SD slot is powered via GPIO0_A1 to a fixed 3.0 V supply. SPL may attempt
> MMC initialization **before this supply has fully stabilized**, resulting in
> a generic I/O error (`-5`). The SD card itself and the controller are
> functioning correctly once the supply is stable.
> 
> **Workarounds / fixes observed:**
> - Add a small delay after enabling `vcc3v0_sd` before SPL starts MMC init.
> - Ensure the regulator is fully powered and stable at SPL start.
> 
> This appears to be a **hardware/platform-specific power-on timing issue**
> rather than a device tree or software bug, but documenting it would help
> users encountering similar errors on the NanoPi NEO4.
> 
> **Hardware:** FriendlyARM NanoPi NEO4
> **SoC:** Rockchip RK3399
> **U-Boot version:** v2026.01-rc1-00070-ge34d01d23e45
> **Reproducibility:** 100% with SD boot

Adding the board maintainer and come other active rockchip people.

-- 
Tom
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