In your dts file, please define FSPI flash device and configure "compatible" property according to the flash device on your target board. Please refer to the following example, please refer to SPI NOR flash driver drivers/mtd/spi-nor/spi-nor.c.
&fspi {
status = "okay";
mt35xu512aba0: flash@0 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "spansion,m25p80";
m25p,fast-read;
spi-max-frequency = <50000000>;
reg = <0>;
spi-rx-bus-width = <8>;
spi-tx-bus-width = <8>;
};
mt35xu512aba1: flash@1 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "spansion,m25p80";
m25p,fast-read;
spi-max-frequency = <50000000>;
reg = <1>;
spi-rx-bus-width = <8>;
spi-tx-bus-width = <8>;
};
};