OpenWrt 18.06: how to add a support of SDHC/SDXC cards?



I'm using GL.iNet GL-AR750 with OpenWrt 18.06.0. The device has a SD card slot (as I understand internally it's connected to GL857L chip). The SDHC/SDXC support in the OS seems to be completely missing - no messages in dmesg when I insert an SD card, partitions don't appear in /dev after a reboot, etc.

I have the following packages installed:

opkg update
opkg install kmod-scsi-core kmod-scsi-generic \
  kmod-usb-core kmod-usb-ohci kmod-usb-uhci kmod-usb2 kmod-usb3 \
  kmod-fs-msdos kmod-fs-vfat kmod-fs-ext4 usbutils \
  kmod-usb-storage kmod-usb-storage-extras block-mount

I can work with USB flash drives with no problem. Do I miss some packages required for SD cards, or maybe GL857L is not currently supported in OpenWrt?