SD card access on Hnet HW-C108

I got this neat battery powered travel router and got all the networking functions working. If anybody is interested in this device, read my description and hints for installation in the thread New Battery Power Router? .

I'm still trying to get SD access working in the C108. I installed kmod-mmc, kmod-mmc-spi, and mmc-utils. However, when those modules are inserted into the kernel there is no output from the kernel (dmesg) at all, apart from the generic message that a module was inserted. No /dev/mmc* nodes show up.

I realise I may need to supply some parameters to the kernel modules. However I found an amazing shortage of documentation on the mmc drivers. How to proceed?

The only bit of mmc documentation for OpenWRT I could find refers to an obsolete kmod-mmc-gpio driver. Not only is this driver lacking in the v19.07.2 repository, it also requires specific information on how the SD card is wired up to the CPU. I do not have schematics, of course.

Any ideas?

Hi, how to solve the SD card interface?

 kern.err kernel: [   29.331001] msdc0 -> TUNE_CMD app_cmd<55> failed: RESP_RXDLY<15>,R_SMPL<1> <- msdc_tune_cmdrsp() : L<1344> PID<kworker/0:1><0x84>
 kern.warn kernel: [   29.351197] mtk-sd 10130000.sdhci: no support for card's volts
 kern.err kernel: [   29.357154] mmc0: error -22 whilst initialising MMC card