In roc-rk3328-cc board, the signal voltage of sdmmc is supplied by the vcc_sdio regulator, which is a mux between 1.8V and 3.3V, controlled by a special output only gpio pin labeled "gpiomut_pmuio_iout", corresponding bit 1 of the syscon GRF_SOC_CON10.
https://patchwork.kernel.org/patch/10550013/
original kernel also changed the file drivers/regulator/gpio-regulator.c in commet https://github.com/rockchip-linux/kernel/commit/b989ade19312ecf57f993120b9668b9d1d3fd380
magic0whi got a reaction from JMCC in Librecomputer Renegade RK3328