There is a detailed description in the wiki, please refer to the wiki
https://wiki.luckfox.com/Luckfox-Pico/L ... munication

Thank you very much, I have add the spi slave driver successfully. and I can get the spi device here
# ls /dev/spidev0.0
/dev/spidev0.0
I use the spi_mode_1, pico luckfox as a slave and arduino uno r4 as a master.
The master send 0xaa, 0x55 and 0x5a three bytes to the slave.
I found a issue， when I send the three bytes single. First time, the slave revice six bytes:0x75 0x64 0x69 0xAA 0x55 0x5A
When i send the three bytes second, the slave can receive 0xAA 0x55 0x5A 0xAA 0x55 0x5A very werid issue.
# ./spi_slave
ret: 3
receive data number: 3
---------Receive 3 bytes of data max speed:1000000 Hz---------
75 62 69
ret: 3
receive data number: 3
---------Receive 3 bytes of data max speed:1000000 Hz---------
AA 55 5A
ret: 3
receive data number: 3
---------Receive 3 bytes of data max speed:1000000 Hz---------
AA 55 5A
ret: 3
receive data number: 3
---------Receive 3 bytes of data max speed:1000000 Hz---------
AA 55 5A

master code :
SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE1));
digitalWrite(7, LOW); // enable Slave Select
delay(1);

// send test string
SPI.transfer(0xAA);
SPI.transfer(0x55);
SPI.transfer(0x5a);

digitalWrite(7, HIGH); // disable Slave Select
SPI.endTransaction();


Slave code :
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/spi/spidev.h>
#include <sys/ioctl.h>
#include <string.h>

#define SPI_DEVICE_PATH "/dev/spidev0.0"

int main() {
int spi_file,ret;
uint8_t tx_buffer[3];
uint8_t rx_buffer[3];

/* Open the SPI device */
if ((spi_file = open(SPI_DEVICE_PATH, O_RDWR)) < 0) {
perror("Failed to open SPI device");
return -1;
}

/* Configure SPI mode and bits per word */
uint8_t mode = SPI_MODE_1;
uint8_t bits = 8;
if (ioctl(spi_file, SPI_IOC_WR_MODE, &mode) < 0) {
perror("Failed to set SPI mode");
close(spi_file);
return -1;
}
if (ioctl(spi_file, SPI_IOC_WR_BITS_PER_WORD, &bits) < 0) {
perror("Failed to set SPI bits per word");
close(spi_file);
return -1;
}

/* Perform SPI transfer */
struct spi_ioc_transfer transfer = {
.tx_buf = (unsigned long)tx_buffer,
.rx_buf = (unsigned long)rx_buffer,
.len = sizeof(rx_buffer),
.delay_usecs = 0,
.speed_hz = 1000000, // SPI speed in Hz
.bits_per_word = 8,
};

while(1)
{
/* Clear buffer */
memset(rx_buffer,0,sizeof(rx_buffer));

/* Waiting for data */
do {
ret = ioctl(spi_file, SPI_IOC_MESSAGE(1), &transfer);
printf("ret: %d\r\n",ret);
} while (ret < 0);

/* Print rx_buffer*/
printf("receive data number: %d\r\n",ret);
printf("---------Receive %d bytes of data max speed:%d Hz---------\n",ret,transfer.speed_hz);
for (int i = 0; i < ret; i++) {
printf(" %02X",rx_buffer );
}
printf("\n");
}

/* Close the SPI device */
close(spi_file);

return 0;
}

1. Try extending the delay time after "enable Slave Select".
2. Attempt to reduce the communication frequency.