Hi,
to avoid the "Write Protected" report is necessary to add following into *.dsc file (new lines marked as bold):
giMXPlatformTokenSpaceGuid.PcdSdhc2Enable|TRUE
giMXPlatformTokenSpaceGuid.PcdSdhc2CardDetectSignal|0xFF00
giMXPlatformTokenSpaceGuid.PcdSdhc2WriteProtectSignal|0xFF00
EVK_iMX6ULL_512MB.dsc is located here:
imx-edk2-platforms/Platform/NXP/EVK_iMX6ULL_512MB/EVK_iMX6ULL_512MB.dsc
UEFI image (uefi.fit) must be updated after this step. You can copy it into UEFI partiton on sd card. For ffu image is necessary to have the updated version here:
imx-iotcore\build\board\EVK_iMX6ULL_512MB\Package\BootFirmware\uefi.fit
bets regards
Vojtech Filip