I did a micro sd card hack on a ancient d-link dir-615 (rev. h1). I used this instruction for the hardware wiring (https://wiki.openwrt.org/toh/d-link/dir-615#sd-card_in_dir-615_h1) and added a micro sd card shield board (something like this: https://www.aliexpress.com/item/Free-shipping-SPI-Micro-SD-Storage-Mciro-SD-TF-Card-Memory-Shield-Module-for-Arduino/32382166628.html)
Here are some pictures:
The instruction for the software part is quite short:
and use the mmc-over-gpio kernel module. The kmod-leds-gpio and kmod-input-gpio-keys-polled kernel modules have to be unloaded before
I now have the question how to get the micro sd card running in the most recent LEDE. I didn't find any mmc-over-gpio package! Any help is appreciated!