The Zero3 MicroSD card slot supports SDR104 but the maximum frequency is set to 150 MHz
I have created an overlay to enable the 208Mhz max-frequency. Be aware that the actual frequency might differ because it depends on the CPU frequency (don’t know the exact ratio)
For future reference I have documented the steps:
Using the Radxa Debian XFCE B4 image
in home folder create following dts file
radxa@radxa-zero3:~$ cat radxa-zero3-sdslot-208mhz.dts
/dts-v1/;
/plugin/;
/ {
metdata {
title = "Set SD card slot freq to 208MHz";
compatible = "radxa,zero3";
category = "misc";
description = "Set SD card slot freq to 208MHz";
};
fragment@0 {
target = <&sdmmc0>;
__overlay__ {
max-frequency = <208000000>;
};
};
};
compile
dtc -@ -H epapr -O dtb -o radxa-zero3-sdslot-208mhz.dtbo -Wno-unit_address_vs_reg radxa-zero3-sdslot-208mhz.dts
move to correct folder and disable (by renaming the file -> this will allow the rsetup utility to correctly identify the file)
sudo mv radxa-zero3-sdslot-208mhz.dtbo /boot/dtbo/radxa-zero3-sdslot-208mhz.dtbo.disabled
give correct permissions
sudo chmod 755 /boot/dtbo/radxa-zero3-sdslot-208mhz.dtbo.disabled
enable using sudo rsetup and reboot
BEFORE
radxa@radxa-zero3:~$ sudo dmesg | grep -i mmc1
[ 12.244192] mmc_host mmc1: Bus speed (slot 0) = 375000Hz (slot req 400000Hz, actual 375000HZ div = 0)
[ 12.862919] mmc1: delay init for 600 ms to enable UHS mode
[ 12.932561] mmc_host mmc1: Bus speed (slot 0) = **148500000Hz** (slot req 150000000Hz, actual 148500000HZ div = 0)
[ 13.072716] mmc1: new ultra high speed SDR104 SDXC card at address 0001
[ 13.074651] mmcblk1: mmc1:0001 FD4Q9 119 GiB
AFTER
radxa@radxa-zero3:~$ sudo dmesg | grep -i mmc1
[ 12.282628] mmc_host mmc1: Bus speed (slot 0) = 375000Hz (slot req 400000Hz, actual 375000HZ div = 0)
[ 12.901357] mmc1: delay init for 600 ms to enable UHS mode
[ 12.972786] mmc_host mmc1: Bus speed (slot 0) = **198000000Hz** (slot req 208000000Hz, actual 198000000HZ div = 0)
[ 13.090046] mmc1: new ultra high speed SDR104 SDXC card at address 0001
[ 13.091765] mmcblk1: mmc1:0001 FD4Q9 119 GiB
Maybe not the correct os supported way but it works in my case 