Rockchip "error -110 whilst initialising SD card": SD Card Not Working

Symptoms

Kernel prints "error -110 whilst initialising SD card"
U-Boot shows "Card did not respond to voltage select! : -110"

Common causes

vqmmc-supply / IO-domain not switching 3.3 V ↔ 1.8 V for UHS modes
Card-detect GPIO polarity wrong
Bus speed modes (sd-uhs-sdr104) enabled on a board that cannot run them
Faulty or incompatible card

How to fix it

Try another card and a lower speed
Remove UHS mode properties temporarily to fall back to high-speed mode.
```
&sdmmc {
    /delete-property/ sd-uhs-sdr104;
    max-frequency = <50000000>;
};
```
Check IO voltage switching
Make sure vqmmc-supply points at a regulator that can switch between 3.3 V and 1.8 V, and that the io-domains node lists the SD bank correctly.
Verify card-detect
```
cat /sys/kernel/debug/mmc0/ios
```

Go deeper

Rockchip Boot Process Explained: BootROM, TPL, SPL, BL31, U-Boot and Linux

FAQ

What does "mmc0: error -110 whilst initialising SD card" mean?

The SD/MMC controller timed out (-110 = ETIMEDOUT) talking to the card. Common causes are IO voltage (vqmmc) configuration, card-detect or bus timing.

What causes "mmc0: error -110 whilst initialising SD card"?

vqmmc-supply / IO-domain not switching 3.3 V ↔ 1.8 V for UHS modes; Card-detect GPIO polarity wrong; Bus speed modes (sd-uhs-sdr104) enabled on a board that cannot run them; Faulty or incompatible card.

How do I fix "mmc0: error -110 whilst initialising SD card"?

1. Try another card and a lower speed: Remove UHS mode properties temporarily to fall back to high-speed mode. 2. Check IO voltage switching: Make sure vqmmc-supply points at a regulator that can switch between 3.3 V and 1.8 V, and that the io-domains node lists the SD bank correctly. 3. Verify card-detect