[課程筆記]Linux Driver正點原子課程筆記4 - Led燈驅動實驗

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Course 4 - Led燈驅動實驗

嘗試透過driver去操作led register來達到led開關的實驗。

地址映射

Linux下無法直接對physical address做讀寫操作，因為linux會enable MMU(Memory Manage Unit)，MMU的功能為

virtual address (VA) <-> physical address (PA)的mapping
內存保護、register的訪問權限

對於32 bit的processor來說，virtual address的range是2^32=4GB。假設開發版有512MB的physical address，則MMU可以將512MB映射到4GB的虛擬空間。

但PA有512MB，VA有4GB，要如何mapping? 這邊先不討論，有興趣的可以去看MMU的詳細介紹

因此，如果要對physical address做讀寫，必須要該PA對應的VA，這邊會用到兩個function:

ioremap(): 獲得PA對應的VA
- 第一個參數: 物理地址起始位置，第二個參數: 轉換的char數量
iounmap(): 釋放VA
- 參數:要釋放的VA

/* arch/arm/include/asm/io.h */
void __iomem *ioremap(resource_size_t res_cookie, size_t size);
#define ioremap ioremap
#define ioremap_nocache ioremap

...

void iounmap(volatile void __iomem *iomem_cookie);
#define iounmap iounmap

/* arch/arm/mm/ioremap.c */
void __iomem *ioremap(resource_size_t res_cookie, size_t size)
{
    return arch_ioremap_caller(res_cookie, size, MT_DEVICE,
                   __builtin_return_address(0));
}

接下來按照影片教學，試著寫一套驅動&app來透過他們家的開發版操控led燈，但我沒有他們的開發版，所以就照著寫了一遍code練習

裡面register的addr是參照影片來寫的，所以如果不能動不要問這值是哪裡來的
Ｑ＿Ｑ

driver

init相關設置(e.g. init led燈需要init gpio, clk..)可以放在*fops的open或module init，端看情境
- 初始化如需讀寫register，記得要取得PA對應的VA
linux不推薦直接對取得的va addr做讀寫，而是用提供的api來操作(readb(), readw(), readl(), writeb(), writew(), writel())
關燈的控制不能寫在led_release()，why?
- 因為如果寫在led_release()，每次app close()時都會關閉燈，情境上不太適合

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/io.h>

#define LED_MAJOR 200
#define LED_NAME "led"

/* register PA */
#define CCM_CCGR1_BASE         (0x020C406C)
#define SW_MUX_GPIO1_IO03_BASE (0x020E0068)
#define SW_PAD_GPIO1_IO03_BASE (0x020E02F4)
#define GPIO1_DR_BASE          (0x0209C000)
#define GPIO1_GDIR_BASE        (0x0209C004)

/* pointer of VA */
static void __iomem *IMX6U_CCM_CCGR1;
static void __iomem *SW_MUX_GPIO1_IO03;
static void __iomem *SW_PAD_GPIO1_IO03;
static void __iomem *GPIO1_DR;
static void __iomem *GPIO1_GDIR;

#define LEDOFF 0
#define LEDON 1

void led_switch(u8 sta)
{
    u32 val = 0;
    if (databuf[0] == LEDOFF) {
        val = readl(GPIO1_DR);
        val |= ~(1 << 3);
        writel(val, GPIO1_DR); // close led
    } else {
        val = readl(GPIO1_DR);
        val &= ~(1 << 3);
        writel(val, GPIO1_DR); // open led
    }
}

static int led_open(struct inode *inode, struct file *filp)
{
    return 0;
}

static int led_release(struct inode *inode, struct file *filp)
{   
    return 0;
}

static ssize_t led_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{
    int ret;
    int val = 0;
    unsigned char databuf[1];
    ret = copy_from_user(databuf, buf, count);
    if (ret < 0){
        printk("kernel write fail\n");
        return -EFAULT;
    }
    
    led_switch(databuf[0]);
    
    return 0;
}

static const struct file_operations *fops 
{
    .owner   = THIS_MODULE,
    .write   = led_write,
    .open    = led_open,
    .release = led_close,
};

static int __init led_init(void)
{
    int ret = 0;
    int val = 0;
    printk("led init\n");
    
    /* 1. get va of register */
    IMX6U_CCM_CCGR1 = ioremap(CCM_CCGR1_BASE, 4);
    SW_MUX_GPIO1_IO03 = ioremap(SW_MUX_GPIO1_IO03_BASE, 4);
    SW_PAD_GPIO1_IO03 = ioremap(SW_PAD_GPIO1_IO03_BASE, 4);
    GPIO1_DR = ioremap(GPIO1_DR_BASE, 4);
    GPIO1_GDIR = ioremap(GPIO1_GDIR_BASE, 4);
    
    /* 2. init */
    val = readl(IMX6U_CCM_CCGR1);
    val &= ~(3 << 26); // clr IMX6U_CCM_CCGR1[26:27]
    val |= 3 << 26; // set IMX6U_CCM_CCGR1[26:27] to 1
    writel(val, IMX6U_CCM_CCGR1);
    
    writel(0x5, SW_MUX_GPIO1_IO03);
    writel(0x10B0, SW_PAD_GPIO1_IO03);
  
    val = readl(GPIO1_GDIR);
    val |= 1 << 3;
    writel(val, GPIO1_GDIR);
  
    val = readl(GPIO1_DR);
    val &= ~(1 << 3);
    writel(val, GPIO1_DR); // open led
  
    /* 2. register chrdev */
    ret = register_chrdev(LED_MAJOR, LED_NAME, &fops);
    if (ret < 0) {
        printk("chrdev register fail\n");
        return -EIO;
    }
        
}

static void __exit led_exit(void)
{
    int val = 0;
    val = readl(GPIO1_DR);
    val |= ~(1 << 3);
    writel(val, GPIO1_DR); // close led
    
    /* 1. unmap va */
    iounmap(IMX6U_CCM_CCGR1);
    iounmap(SW_MUX_GPIO1_IO03);
    iounmap(SW_PAD_GPIO1_IO03);
    iounmap(GPIO1_DR);
    iounmap(GPIO1_GDIR);
    
    /* 2. unregister */
    unregister_chrdev(LED_MAJOR, LED_NAME);
    printk("chrdev unregister\n");
}

module_init(led_init);
module_exit(led_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("john");

app

/**
 * ./ledAPP <filename> <num>
 * @num: 0 代表關燈, 1代表開燈
 */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define LEDOFF 0
#define LEDON 1

int main(int argc, char *argv[]) 
{
    int fd = 0;
    int ret = 0;
    char *filename;
    unsigned char databuf[1];
    
    if (argc != 3) return -1;
    
    filename = argv[1];
    
    /* open() return a file descriptor */
    fd = open(filename, O_RDWR);
    
    if (fd < 0)
        printf("Can not open file %s\n", filename);
        return -1;
    
    databuf[0] = atoi(argv[2]);
    ret = write(fd, databuf, sizeof(databuf));
    if (ret < 0) {
        printk("led control fail\n");
        close(fd);
        return -1;
    }
    
    close(fd);
    
    return 0;
}