STM32U5 SDMMC1 & 4-wired MicroSD

[devin-hu]

Hello,

I am currently using an STM32U5G9 and would like to connect a microSD card via SDMMC1 to expand data storage. My Zephyr device tree contains the following node:

&sdmmc1 {
 status = "okay";
 pinctrl-0 = <&sdmmc1_d0_pc8 &sdmmc1_d1_pc9 &sdmmc1_d2_pc10 &sdmmc1_d3_pc11
 &sdmmc1_ck_pc12 &sdmmc1_cmd_pd2>;
 pinctrl-names = "default";
 disk-name = "SD";
 bus-width = <1>;
 clk-div = <8>;
};

As shown above, bus-width = <1> indicates 1-bit (1-line) mode. I would like to use 4-bit mode, but after changing this value to <4>, the microSD card can no longer be accessed.

How should this issue be resolved, and what additional configuration or considerations are required to enable 4-bit SDMMC operation correctly on STM32U5 with Zephyr?