Lab: điều khiển LED bằng kernel module

1// led_kmod.c – điều khiển LED ở GPIO17 qua thanh ghi (Pi Zero 2 W)
2#include <linux/module.h>
3#include <linux/miscdevice.h>
4#include <linux/fs.h>
5#include <linux/io.h>
6#include <linux/bits.h>
7#include <linux/uaccess.h>
8 
9#define GPIO_PHYS 0x3F200000   /* 0x3F000000 + 0x200000 */
10#define GPIO_SIZE 0x100
11#define GPFSEL1   0x04
12#define GPSET0    0x1C
13#define GPCLR0    0x28
14#define GPLEV0    0x34
15#define LED_PIN   17
16 
17static void __iomem *gpio;
18 
19static ssize_t led_write(struct file *f, const char __user *buf,
20                         size_t n, loff_t *off)
21{
22    char c;
23    if (!n || get_user(c, buf))
24        return -EFAULT;
25    if (c == '1')
26        writel(BIT(LED_PIN), gpio + GPSET0);
27    else if (c == '0')
28        writel(BIT(LED_PIN), gpio + GPCLR0);
29    return n;
30}
31 
32static ssize_t led_read(struct file *f, char __user *buf,
33                        size_t n, loff_t *off)
34{
35    char s[2] = { '0', '\n' };
36    if (readl(gpio + GPLEV0) & BIT(LED_PIN))
37        s[0] = '1';
38    return simple_read_from_buffer(buf, n, off, s, 2);
39}
40 
41static const struct file_operations led_fops = {
42    .owner = THIS_MODULE,
43    .write = led_write,
44    .read  = led_read,
45};
46static struct miscdevice led_dev = {
47    .minor = MISC_DYNAMIC_MINOR,
48    .name  = "led",            /* → /dev/led */
49    .fops  = &led_fops,
50};
51 
52static int __init led_init(void)
53{
54    u32 v;
55    gpio = ioremap(GPIO_PHYS, GPIO_SIZE);
56    if (!gpio)
57        return -ENOMEM;
58    v = readl(gpio + GPFSEL1);          /* GPIO17: bit 23:21 */
59    v &= ~(7 << 21);
60    v |=  (1 << 21);                    /* 001 = output */
61    writel(v, gpio + GPFSEL1);
62    return misc_register(&led_dev);
63}
64 
65static void __exit led_exit(void)
66{
67    misc_deregister(&led_dev);
68    writel(BIT(LED_PIN), gpio + GPCLR0);   /* tắt LED */
69    writel(readl(gpio + GPFSEL1) & ~(7 << 21), gpio + GPFSEL1);
70    iounmap(gpio);
71}
72 
73module_init(led_init);
74module_exit(led_exit);
75MODULE_LICENSE("GPL");