I fooled around with the information I found here
https://discourse.coreelec.org/t/19-0-matrix-discussion/14774/432
and tried to activate the “sd-uhs-sdr25” mode. Now dmesg tells me that the system cannot switch to the ( lower ) voltage the UHS mode needs ( 1,8V instead of 3,3V )
After that I compared the dtb from Ubuntu for the odroid HC4 ( which claims to achieve full UHD SDR104 speed ) and found to more entrys in this dtb, thats
vol_switch = <0x11 0x06 0x00>;
vol_switch_18 = <0x01>;
but now dmesg tells me, that in cannot find the correct GPIO pins to execute this commands. Any idea ?