In order to use the SPI, you need to enable the SPI function via Device Tree Overlay.

overlays=spi1

$ ls /dev/spidev1.1
/dev/spidev1.1

fdt_overlays=spi1

fdt_overlays=spi1

fdt_overlays=spi0

$ ls /dev/spidev1.0 
/dev/spidev1.0

fdt_overlays=spi0

$ ls /dev/spidev1.0 
/dev/spidev1.0

If you want to use normal GPIO instead of SPI, you can remove the SPI node in Device Tree Overlay.

spidev_test.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * SPI testing utility (using spidev driver)
 *
 * Copyright (c) 2007  MontaVista Software, Inc.
 * Copyright (c) 2007  Anton Vorontsov <avorontsov@ru.mvista.com>
 *
 * Cross-compile with cross-gcc -I/path/to/cross-kernel/include
 */
 
#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <fcntl.h>
#include <time.h>
#include <sys/ioctl.h>
#include <linux/ioctl.h>
#include <sys/stat.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>
 
#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
 
static void pabort(const char *s)
{
    perror(s);
    abort();
}
 
static const char *device = "/dev/spidev1.0";
static uint32_t mode;
static uint8_t bits = 8;
static char *input_file;
static char *output_file;
static uint32_t speed = 500000;
static uint16_t delay;
static int verbose;
static int transfer_size;
static int iterations;
static int interval = 5; /* interval in seconds for showing transfer rate */
 
uint8_t default_tx[] = {
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xF0, 0x0D,
};
 
uint8_t default_rx[ARRAY_SIZE(default_tx)] = {0, };
char *input_tx;
 
static void hex_dump(const void *src, size_t length, size_t line_size,
             char *prefix)
{
    int i = 0;
    const unsigned char *address = src;
    const unsigned char *line = address;
    unsigned char c;
 
    printf("%s | ", prefix);
    while (length-- > 0) {
        printf("%02X ", *address++);
        if (!(++i % line_size) || (length == 0 && i % line_size)) {
            if (length == 0) {
                while (i++ % line_size)
                    printf("__ ");
            }
            printf(" |");
            while (line < address) {
                c = *line++;
                printf("%c", (c < 32 || c > 126) ? '.' : c);
            }
            printf("|\n");
            if (length > 0)
                printf("%s | ", prefix);
        }
    }
}
 
/*
 *  Unescape - process hexadecimal escape character
 *      converts shell input "\x23" -> 0x23
 */
static int unescape(char *_dst, char *_src, size_t len)
{
    int ret = 0;
    int match;
    char *src = _src;
    char *dst = _dst;
    unsigned int ch;
 
    while (*src) {
        if (*src == '\\' && *(src+1) == 'x') {
            match = sscanf(src + 2, "%2x", &ch);
            if (!match)
                pabort("malformed input string");
 
            src += 4;
            *dst++ = (unsigned char)ch;
        } else {
            *dst++ = *src++;
        }
        ret++;
    }
    return ret;
}
 
static void transfer(int fd, uint8_t const *tx, uint8_t const *rx, size_t len)
{
    int ret;
    int out_fd;
    struct spi_ioc_transfer tr = {
        .tx_buf = (unsigned long)tx,
        .rx_buf = (unsigned long)rx,
        .len = len,
        .delay_usecs = delay,
        .speed_hz = speed,
        .bits_per_word = bits,
    };
 
    if (mode & SPI_TX_QUAD)
        tr.tx_nbits = 4;
    else if (mode & SPI_TX_DUAL)
        tr.tx_nbits = 2;
    if (mode & SPI_RX_QUAD)
        tr.rx_nbits = 4;
    else if (mode & SPI_RX_DUAL)
        tr.rx_nbits = 2;
    if (!(mode & SPI_LOOP)) {
        if (mode & (SPI_TX_QUAD | SPI_TX_DUAL))
            tr.rx_buf = 0;
        else if (mode & (SPI_RX_QUAD | SPI_RX_DUAL))
            tr.tx_buf = 0;
    }
 
    ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
    if (ret < 1)
        pabort("can't send spi message");
 
    if (verbose)
        hex_dump(tx, len, 32, "TX");
 
    if (output_file) {
        out_fd = open(output_file, O_WRONLY | O_CREAT | O_TRUNC, 0666);
        if (out_fd < 0)
            pabort("could not open output file");
 
        ret = write(out_fd, rx, len);
        if (ret != len)
            pabort("not all bytes written to output file");
 
        close(out_fd);
    }
 
    if (verbose)
        hex_dump(rx, len, 32, "RX");
}
static void print_usage(const char *prog)
{
    printf("Usage: %s [-DsbdlHOLC3vpNR24SI]\n", prog);
    puts("  -D --device   device to use (default /dev/spidev1.1)\n"
         "  -s --speed    max speed (Hz)\n"
         "  -d --delay    delay (usec)\n"
         "  -b --bpw      bits per word\n"
         "  -i --input    input data from a file (e.g. \"test.bin\")\n"
         "  -o --output   output data to a file (e.g. \"results.bin\")\n"
         "  -l --loop     loopback\n"
         "  -H --cpha     clock phase\n"
         "  -O --cpol     clock polarity\n"
         "  -L --lsb      least significant bit first\n"
         "  -C --cs-high  chip select active high\n"
         "  -3 --3wire    SI/SO signals shared\n"
         "  -v --verbose  Verbose (show tx buffer)\n"
         "  -p            Send data (e.g. \"1234\\xde\\xad\")\n"
         "  -N --no-cs    no chip select\n"
         "  -R --ready    slave pulls low to pause\n"
         "  -2 --dual     dual transfer\n"
         "  -4 --quad     quad transfer\n"
         "  -S --size     transfer size\n"
         "  -I --iter     iterations\n");
    exit(1);
}
 
static void parse_opts(int argc, char *argv[])
{
    while (1) {
        static const struct option lopts[] = {
            { "device",  1, 0, 'D' },
            { "speed",   1, 0, 's' },
            { "delay",   1, 0, 'd' },
            { "bpw",     1, 0, 'b' },
            { "input",   1, 0, 'i' },
            { "output",  1, 0, 'o' },
            { "loop",    0, 0, 'l' },
            { "cpha",    0, 0, 'H' },
            { "cpol",    0, 0, 'O' },
            { "lsb",     0, 0, 'L' },
            { "cs-high", 0, 0, 'C' },
            { "3wire",   0, 0, '3' },
            { "no-cs",   0, 0, 'N' },
            { "ready",   0, 0, 'R' },
            { "dual",    0, 0, '2' },
            { "verbose", 0, 0, 'v' },
            { "quad",    0, 0, '4' },
            { "size",    1, 0, 'S' },
            { "iter",    1, 0, 'I' },
            { NULL, 0, 0, 0 },
        };
        int c;
 
        c = getopt_long(argc, argv, "D:s:d:b:i:o:lHOLC3NR24p:vS:I:",
                lopts, NULL);
 
        if (c == -1)
            break;
 
        switch (c) {
        case 'D':
            device = optarg;
            break;
        case 's':
            speed = atoi(optarg);
            break;
        case 'd':
            delay = atoi(optarg);
            break;
        case 'b':
            bits = atoi(optarg);
            break;
        case 'i':
            input_file = optarg;
            break;
        case 'o':
            output_file = optarg;
            break;
        case 'l':
            mode |= SPI_LOOP;
            break;
        case 'H':
            mode |= SPI_CPHA;
            break;
        case 'O':
            mode |= SPI_CPOL;
            break;
        case 'L':                                                          
             mode |= SPI_LSB_FIRST;
             break;
         case 'C':
             mode |= SPI_CS_HIGH;
             break;
         case '3':
             mode |= SPI_3WIRE;
             break;
         case 'N':
             mode |= SPI_NO_CS;
             break;
         case 'v':
             verbose = 1;
             break;
         case 'R':
             mode |= SPI_READY;
             break;
         case 'p':
             input_tx = optarg;
             break;
         case '2':
             mode |= SPI_TX_DUAL;
             break;
         case '4':
             mode |= SPI_TX_QUAD;
             break;
         case 'S':
             transfer_size = atoi(optarg);
             break;
         case 'I':
             iterations = atoi(optarg);
             break;
         default:
             print_usage(argv[0]);
             break;
         }
     }
     if (mode & SPI_LOOP) {
         if (mode & SPI_TX_DUAL)
             mode |= SPI_RX_DUAL;
         if (mode & SPI_TX_QUAD)
             mode |= SPI_RX_QUAD;
     }
 }
 
 static void transfer_escaped_string(int fd, char *str)
 {
     size_t size = strlen(str);
     uint8_t *tx;
     uint8_t *rx;
 
     tx = malloc(size);
     if (!tx)
         pabort("can't allocate tx buffer");
 
     rx = malloc(size);
     if (!rx)
         pabort("can't allocate rx buffer");
 
     size = unescape((char *)tx, str, size);
     transfer(fd, tx, rx, size);
     free(rx);
     free(tx);
 }
 
static void transfer_file(int fd, char *filename)
{
    ssize_t bytes;
    struct stat sb;
    int tx_fd;
    uint8_t *tx;
    uint8_t *rx;
 
    if (stat(filename, &sb) == -1)
        pabort("can't stat input file");
 
    tx_fd = open(filename, O_RDONLY);
    if (tx_fd < 0)
        pabort("can't open input file");
 
    tx = malloc(sb.st_size);
    if (!tx)
        pabort("can't allocate tx buffer");
 
    rx = malloc(sb.st_size);
    if (!rx)
        pabort("can't allocate rx buffer");
 
    bytes = read(tx_fd, tx, sb.st_size);
    if (bytes != sb.st_size)
        pabort("failed to read input file");
 
    transfer(fd, tx, rx, sb.st_size);
    free(rx);
    free(tx);
    close(tx_fd);
}
 
static uint64_t _read_count;
static uint64_t _write_count;
 
static void show_transfer_rate(void)
{
    static uint64_t prev_read_count, prev_write_count;
    double rx_rate, tx_rate;
 
    rx_rate = ((_read_count - prev_read_count) * 8) / (interval*1000.0);
    tx_rate = ((_write_count - prev_write_count) * 8) / (interval*1000.0);
 
    printf("rate: tx %.1fkbps, rx %.1fkbps\n", rx_rate, tx_rate);
 
    prev_read_count = _read_count;
    prev_write_count = _write_count;
}
 
static void transfer_buf(int fd, int len)
{
    uint8_t *tx;
    uint8_t *rx;
    int i;
 
    tx = malloc(len);
    if (!tx)
        pabort("can't allocate tx buffer");
    for (i = 0; i < len; i++)
        tx[i] = random();
 
    rx = malloc(len);
    if (!rx)
        pabort("can't allocate rx buffer");
 
    transfer(fd, tx, rx, len);
 
    _write_count += len;
    _read_count += len;
 
    if (mode & SPI_LOOP) {
        if (memcmp(tx, rx, len)) {
            fprintf(stderr, "transfer error !\n");
            hex_dump(tx, len, 32, "TX");
            hex_dump(rx, len, 32, "RX");
            exit(1);
        }
    }
 
    free(rx);
    free(tx);
}
int main(int argc, char *argv[])
{
    int ret = 0;
    int fd;
 
    parse_opts(argc, argv);
 
    fd = open(device, O_RDWR);
    if (fd < 0)
        pabort("can't open device");
 
    /*
     * spi mode
     */
    ret = ioctl(fd, SPI_IOC_WR_MODE32, &mode);
    if (ret == -1)
        pabort("can't set spi mode");
 
    ret = ioctl(fd, SPI_IOC_RD_MODE32, &mode);
    if (ret == -1)
        pabort("can't get spi mode");
 
    /*
     * bits per word
     */
    ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
    if (ret == -1)
        pabort("can't set bits per word");
 
    ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
    if (ret == -1)
        pabort("can't get bits per word");
 
    /*
     * max speed hz
     */
    ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
    if (ret == -1)
        pabort("can't set max speed hz");
 
    ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
    if (ret == -1)
        pabort("can't get max speed hz");
 
    printf("spi mode: 0x%x\n", mode);
    printf("bits per word: %d\n", bits);
    printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);
 
    if (input_tx && input_file)
        pabort("only one of -p and --input may be selected");
 
    if (input_tx)
        transfer_escaped_string(fd, input_tx);
    else if (input_file)
        transfer_file(fd, input_file);
    else if (transfer_size) {
        struct timespec last_stat;
 
        clock_gettime(CLOCK_MONOTONIC, &last_stat);
 
        while (iterations-- > 0) {
            struct timespec current;
 
            transfer_buf(fd, transfer_size);
 
            clock_gettime(CLOCK_MONOTONIC, &current);
            if (current.tv_sec - last_stat.tv_sec > interval) {
                show_transfer_rate();
                last_stat = current;
            }
        }
        printf("total: tx %.1fKB, rx %.1fKB\n",
               _write_count/1024.0, _read_count/1024.0);
    } else
        transfer(fd, default_tx, default_rx, sizeof(default_tx));
 
    close(fd);
 
    return ret;
}

Compile test code:

$ gcc -o spidev_test spidev_test.c

Prepare input text file:

$ echo "Amazing Khadas!" > ./spi_in.txt

Connect PIN36(MOSI), PIN37(MISO) then run spidev_test:

$ ./spidev_test -i spi_in.txt -o ./spi_out.txt
spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)

Check output data:

$ cat ./spi_out.txt
Amazing Khadas!