在 Linux 内核上执行 mmap

Question

我正在尝试在 Raspberry pi 上启用上拉，更简单的方法是执行 raspi-gpio set <gpio> <pu/pd>，问题是由于某些原因我无法使用 call_usermodehelper（它不会抛出任何错误，但它什么也不做）。

作为替代方案，我一直在查看 raspi-gpio 源代码，并且我有一个启用上拉的功能 C 代码（此代码打印 GPIO CPU 并启用 GPIO26 的上拉）：

#include <stdio.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <time.h>

// From https://github.com/RPi-Distro/raspi-gpio/blob/master/raspi-gpio.c

#define PULL_UNSET  -1
#define PULL_NONE    0
#define PULL_DOWN    1
#define PULL_UP      2

#define GPIO_BASE_OFFSET 0x00200000
#define GPPUD        37
#define GPPUDCLK0    38

uint32_t getGpioRegBase(void) {
    const char *revision_file = "/proc/device-tree/system/linux,revision";
    uint8_t revision[4] = { 0 };
    uint32_t cpu = 0;
    FILE *fd;

    if ((fd = fopen(revision_file, "rb")) == NULL)
    {
        printf("Can't open '%s'\n", revision_file);
    }
    else
    {
        if (fread(revision, 1, sizeof(revision), fd) == 4)
            cpu = (revision[2] >> 4) & 0xf;
        else
            printf("Revision data too short\n");

        fclose(fd);
    }

    printf("CPU: %d\n", cpu);
    switch (cpu) {
        case 0: // BCM2835 [Pi 1 A; Pi 1 B; Pi 1 B+; Pi Zero; Pi Zero W]
            return 0x20000000 + GPIO_BASE_OFFSET;
        case 1: // BCM2836 [Pi 2 B]
        case 2: // BCM2837 [Pi 3 B; Pi 3 B+; Pi 3 A+]
            return 0x3f000000 + GPIO_BASE_OFFSET;
        case 3: // BCM2711 [Pi 4 B]
            return 0xfe000000 + GPIO_BASE_OFFSET;
        default:
            printf("Unrecognised revision code\n");
            exit(1);
    }
}

volatile uint32_t *getBase(uint32_t reg_base) {
    int fd;
    if ((fd = open ("/dev/mem", O_RDWR | O_SYNC | O_CLOEXEC) ) < 0) return NULL;
    return (uint32_t *)mmap(0, /*chip->reg_size*/ 0x1000,
                                  PROT_READ|PROT_WRITE, MAP_SHARED,
                                  fd, reg_base);
}

void setPull(volatile uint32_t *base, unsigned int gpio, int pull) {
    int clkreg = GPPUDCLK0 + (gpio / 32);
    int clkbit = 1 << (gpio % 32);

    base[GPPUD] = pull;
    usleep(10);
    base[clkreg] = clkbit;
    usleep(10);
    base[GPPUD] = 0;
    usleep(10);
    base[clkreg] = 0;
    usleep(10);
}

int main() {
    uint32_t reg_base = getGpioRegBase();
    volatile uint32_t *base = getBase(reg_base);
    if (base == NULL || base == (uint32_t *)-1) {
    printf("Base error");
        return 1;
    }
    printf("Base: %p\n", base);
    setPull(base, 26, PULL_UP);
    return 0;
}

现在显然我需要将该代码转换为内核代码。我在延迟和文件方面做得很好，但我不知道如何处理 mmap（我以前从未见过它，我也不知道它到底做了什么，我只知道它映射内存）。

#include <linux/types.h>    // uint_32
#include <linux/fs.h>       // filp_open/filp_close
#include <linux/delay.h>    // delay

#define PULL_DOWN    1
#define PULL_UP      2

#define GPIO_BASE_OFFSET 0x00200000
#define GPPUD        37
#define GPPUDCLK0    38

static uint32_t getGpioRegBase(bool *error) {
    uint8_t revision[4] = { 0 };
    uint32_t cpu = 0;
    struct file *fd;
    ssize_t rc = 0;

    if (IS_ERR(( fd = filp_open("/proc/device-tree/system/linux,revision", O_RDONLY | O_SYNC | O_CLOEXEC, 0) ))) {
        *error = true;
        return 0;
    }
    
    if ((rc = kernel_read(fd, revision, sizeof(revision), 0)) == 4) cpu = (revision[2] >> 4) & 0xf;
    else {
        *error = true;
        return 0;
    }

    filp_close(fd, NULL);

    *error = false;
    switch (cpu) {
        case 0: // BCM2835 [Pi 1 A; Pi 1 B; Pi 1 B+; Pi Zero; Pi Zero W]
            return 0x20000000 + GPIO_BASE_OFFSET;
        case 1: // BCM2836 [Pi 2 B]
        case 2: // BCM2837 [Pi 3 B; Pi 3 B+; Pi 3 A+]
            return 0x3f000000 + GPIO_BASE_OFFSET;
        case 3: // BCM2711 [Pi 4 B]
            return 0xfe000000 + GPIO_BASE_OFFSET;
        default:
            *error = true;
            return 0;
    }
}

static volatile uint32_t *getBase(uint32_t reg_base) {
    struct file *fd;
    volatile uint32_t *r;
    
    if (IS_ERR(( fd = filp_open("/dev/mem", O_RDWR | O_SYNC | O_CLOEXEC, 0) ))) return NULL;
    r = (uint32_t*)mmap(0, 0x1000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, reg_base);
    filp_close(fd, NULL); // TODO the original didn't have this
    
    return r;
}

static void setPull(volatile uint32_t *base, uint32_t gpio, int pull) {
    int clkreg = GPPUDCLK0 + (gpio / 32);
    int clkbit = 1 << (gpio % 32);

    base[GPPUD] = pull;
    udelay(10);
    base[clkreg] = clkbit;
    udelay(10);
    base[GPPUD] = 0;
    udelay(10);
    base[clkreg] = 0;
    udelay(10);
}

/**
 * Equivalent to 'raspi-gpio set <gpio> <pu/pd>'
 * @param gpio Valid GPIO pin
 * @param pull PULL_DOWN/PULL_UP
 */
static int setGpioPull(uint32_t gpio, int pull) {
    bool error;
    uint32_t reg_base;
    volatile uint32_t *base;
    
    reg_base = getGpioRegBase(&error);
    if (error) return -1;
    base = getBase(reg_base);
    if (base == NULL || base == (uint32_t*)-1) return -1;
    setPull(base, gpio, pull);
    
    return 0;
}

我发现它只是一个函数声明 (int (*mmap) (struct file *filp, struct vm_area_struct *vma))，但我不知道如何发送任何参数，也不知道如何发送 mmap (caddr_t addr, size_t len, int prot, int flags, int fd, off_t offset) 使用的 return 值.

提前致谢！

Answer 1

Mmap 在 some more questions 之后访问“/dev/mem”，我发现该文件将 user-space 与 kernel-space 连接起来（而 LKM 是在内核 space 上，因此无需访问它）。在这种情况下，ioremap 就可以了。

这是最终代码：

#include <linux/types.h>    // uint_32
#include <linux/fs.h>       // filp_open/filp_close
#include <linux/delay.h>    // udelay
#include <linux/io.h>       // ioremap?

#define PULL_DOWN    1
#define PULL_UP      2


/**
 * Equivalent to 'raspi-gpio set <gpio> <pu/pd>'
 * @param gpio Valid GPIO pin
 * @param pull PULL_DOWN/PULL_UP
 */
static int setGpioPull(uint32_t gpio, int pull);

/****************************
 ***   PRIVATE FUNCTIONS  ***
 ****************************/

#define GPIO_BASE_OFFSET 0x00200000
#define GPPUD        37
#define GPPUDCLK0    38

static uint32_t getGpioRegBase(bool *error) {
    uint8_t revision[4] = { 0 };
    uint32_t cpu = 0;
    struct file *fd;
    ssize_t rc = 0;

    if (IS_ERR(( fd = filp_open("/proc/device-tree/system/linux,revision", O_RDONLY | O_SYNC | O_CLOEXEC, 0) ))) {
        *error = true;
        return 0;
    }
    
    if ((rc = kernel_read(fd, revision, sizeof(revision), 0)) == 4) cpu = (revision[2] >> 4) & 0xf;
    else {
        *error = true;
        return 0;
    }

    filp_close(fd, NULL);

    *error = false;
    switch (cpu) {
        case 0: // BCM2835 [Pi 1 A; Pi 1 B; Pi 1 B+; Pi Zero; Pi Zero W]
            return 0x20000000 + GPIO_BASE_OFFSET;
        case 1: // BCM2836 [Pi 2 B]
        case 2: // BCM2837 [Pi 3 B; Pi 3 B+; Pi 3 A+]
            return 0x3f000000 + GPIO_BASE_OFFSET;
        case 3: // BCM2711 [Pi 4 B]
            return 0xfe000000 + GPIO_BASE_OFFSET;
        default:
            *error = true;
            return 0;
    }
}

static void setPull(volatile uint32_t *base, uint32_t gpio, int pull) {
    int clkreg = GPPUDCLK0 + (gpio / 32);
    int clkbit = 1 << (gpio % 32);

    base[GPPUD] = pull;
    udelay(10);
    base[clkreg] = clkbit;
    udelay(10);
    base[GPPUD] = 0;
    udelay(10);
    base[clkreg] = 0;
    udelay(10);
}

static int setGpioPull(uint32_t gpio, int pull) {
    bool error;
    uint32_t reg_base;
    volatile uint32_t *base;
    
    reg_base = getGpioRegBase(&error);
    if (error) return -1;
    base = (uint32_t*)ioremap(reg_base, 0x1000);
    if (base == NULL || base == (uint32_t*)-1) return -1;
    setPull(base, gpio, pull);
    iounmap(base);
    
    return 0;
}

在 Linux 内核上执行 mmap

Execute mmap on Linux kernel

c

linux-kernel

raspberry-pi

mmap