PCIe驱动开发（4）— DMA驱动编写与测试

Willliam_william2024-07-19 22:11

PCIe驱动开发（4）--- DMA驱动编写与测试

一、前言

代码参考：https://gitee.com/daalw/PCIe_Driver_Demo

二、DMA功能解读

通过查看docs/specs/edu.txt可以知道 EDU 设备是支持DMA的：

与其相关的寄存器有:

另外需要注意的是，该DMA默认只支持 28bit的地址线：

三、驱动编写

编写驱动代码如下所示：

c 复制代码 
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/pci.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/dma-mapping.h>

#define HELLO_PCI_DEVICE_ID     0x11e8
#define HELLO_PCI_VENDOR_ID     0x1234
#define HELLO_PCI_REVISION_ID   0x10

#define ONCHIP_MEM_BASE         0x40000

static struct pci_device_id ids[] = {
    { PCI_DEVICE(HELLO_PCI_VENDOR_ID, HELLO_PCI_DEVICE_ID), },
    { 0 , }
};

static struct hello_pci_info_t {
    dev_t dev_id;
    struct cdev char_dev;
    struct class *class;
    struct device *device;
    struct pci_dev *pdev;
    void __iomem *address_bar0;
    atomic_t dma_running;
    spinlock_t lock;
    wait_queue_head_t r_wait;
} hello_pci_info;

MODULE_DEVICE_TABLE(pci, ids);

static irqreturn_t hello_pci_irq_handler(int irq, void *dev_info)
{
    struct hello_pci_info_t *_pci_info = dev_info;
    uint32_t irq_status;

    // get irq_stutas
    irq_status = *((uint32_t *)(_pci_info->address_bar0 + 0x24));
    printk("hello_pcie: get irq status: 0x%0x\n", irq_status);
    // clean irq
    *((uint32_t *)(_pci_info->address_bar0 + 0x64)) = irq_status;

    // get irq_stutas
    irq_status = *((uint32_t *)(_pci_info->address_bar0 + 0x24));
    if(irq_status == 0x00){
        printk("hello_pcie: receive irq and clean success. \n");
    }else{
        printk("hello_pcie: receive irq but clean failed !!! \n");
        return IRQ_NONE;
    }

    atomic_set(&(_pci_info->dma_running), 0);
    wake_up_interruptible(&(_pci_info->r_wait));

    return IRQ_HANDLED;
}

/*
 * @description     : 打开设备
 * @param - inode   : 传递给驱动的inode
 * @param - file    : 设备文件，file结构体有个叫做private_data的成员变量
 *                    一般在open的时候将private_data指向设备结构体。
 * @return          : 0 成功;其他 失败
 */
static int hello_pcie_open(struct inode *inode, struct file *file)
{
    printk("hello_pcie: open dev file.\n");

    init_waitqueue_head(&hello_pci_info.r_wait);

    return 0;
}

/*
 * @description     : 关闭/释放设备
 * @param - file    : 要关闭的设备文件(文件描述符)
 * @return          : 0 成功;其他 失败
 */
static int hello_pcie_close(struct inode *inode, struct file *file)
{
    printk("hello_pcie: close dev file.\n");

    return 0;
}

//dma transefer from RC to EP
int dma_write_block(dma_addr_t dma_handle_addr, int count, struct hello_pci_info_t *_pci_info)
{
    spin_lock(&_pci_info->lock);

    //源地址低32位
    iowrite32((uint32_t)(dma_handle_addr), _pci_info->address_bar0 + 0x80);
    //源地址高32位
    iowrite32((uint32_t)(dma_handle_addr>>32), _pci_info->address_bar0 + 0x84);
    //目的地址低32位
    iowrite32(ONCHIP_MEM_BASE, _pci_info->address_bar0 + 0x88);
    //目的地址高32位
    iowrite32(0x0, _pci_info->address_bar0 + 0x8c);
    //传输长度
    iowrite32(count, _pci_info->address_bar0 + 0x90);
    //启动DMA一次
    iowrite32((0x01) | (0x00<<1) | (0x01<<2), _pci_info->address_bar0 + 0x98);
    
    spin_unlock(&_pci_info->lock);
    return 0;
}

//dma transefer from EP to RC
int dma_read_block(dma_addr_t dma_handle_addr, int count, struct hello_pci_info_t *_pci_info)
{
    spin_lock(&_pci_info->lock);

    // 源地址低32位
    iowrite32(ONCHIP_MEM_BASE, _pci_info->address_bar0 + 0x80);
    // 源地址高32位
    iowrite32(0, _pci_info->address_bar0 + 0x84);
    // 目的地址低32位
    iowrite32((uint32_t)(dma_handle_addr), _pci_info->address_bar0 + 0x88);
    // 目的地址高32位
    iowrite32((uint32_t)(dma_handle_addr>>32), _pci_info->address_bar0 + 0x8c);
    // 传输长度
    iowrite32(count, _pci_info->address_bar0 + 0x90);
    // 启动DMA一次
    iowrite32((0x01) | (0x01<<1) | (0x01<<2), _pci_info->address_bar0 + 0x98);

    spin_unlock(&_pci_info->lock);
    return 0;
}


/*
 * @description     : 向设备写数据 
 * @param - pfile   : 设备文件，表示打开的文件描述符
 * @param - buf     : 要写给设备写入的数据
 * @param - cnt     : 要写入的数据长度
 * @param - offt    : 相对于文件首地址的偏移
 * @return          : 写入的字节数，如果为负值，表示写入失败
 */
static ssize_t hello_pcie_write(struct file *pfile, const char __user *buf, size_t cnt, loff_t *offt)
{
    int ret;
    unsigned char * databuf;
    dma_addr_t dma_handle_addr;
    
    if(cnt > 4096){
        printk("hello_pcie: dma does not support transfers larger than 4096.\n");
        return -ENOMEM;
    }

    databuf = dma_alloc_coherent(&hello_pci_info.pdev->dev, 4096, &dma_handle_addr, GFP_KERNEL);
    if (!databuf) {
        printk("hello_pcie: Failed to allocate DMA buffer\n");
        return -ENOMEM;
    }
    else {
        printk("hello_pcie: get dma_handle_addr success: 0x%0llx\n", dma_handle_addr);
    }
    ret = copy_from_user(databuf, buf, cnt);
    if(ret < 0) {
        printk("hello_pcie: write failed!\n");
        return -EFAULT;
    }

    dma_write_block(dma_handle_addr, cnt, &hello_pci_info);
    atomic_set(&hello_pci_info.dma_running, 1);

    ret = wait_event_interruptible(hello_pci_info.r_wait, 0 == atomic_read(&hello_pci_info.dma_running));

    dma_free_coherent(&hello_pci_info.pdev->dev, 4096, databuf, dma_handle_addr);
    
    return ret;
}

/*
 * @description     : 从设备读取数据 
 * @param -- filp    : 要打开的设备文件(文件描述符)
 * @param -- buf     : 返回给用户空间的数据缓冲区
 * @param -- cnt     : 要读取的数据长度
 * @param -- offt    : 相对于文件首地址的偏移
 * @return          : 读取的字节数，如果为负值，表示读取失败
 */
static ssize_t hello_pcie_read(struct file *filp, char __user *buf, size_t cnt, loff_t *offt)
{
    int ret;
    unsigned char * databuf;
    dma_addr_t dma_handle_addr;

    if(cnt > 4096){
        printk("hello_pcie: dma does not support transfers larger than 4096.\n");
        return -ENOMEM;
    }

    databuf = dma_alloc_coherent(&hello_pci_info.pdev->dev, 4096, &dma_handle_addr, GFP_KERNEL);
    if (!databuf) {
        printk("hello_pcie: Failed to allocate DMA buffer\n");
        return -ENOMEM;
    }
    else {
        printk("hello_pcie: get dma_handle_addr success: 0x%0llx\n", dma_handle_addr);
    }
    dma_read_block(dma_handle_addr, cnt, &hello_pci_info);
    atomic_set(&hello_pci_info.dma_running, 1);

    /* 加入等待队列，当有DMA传输完成时，才会被唤醒 */
    ret = wait_event_interruptible(hello_pci_info.r_wait, 0 == atomic_read(&hello_pci_info.dma_running));
    if(ret)
        return ret;

    memset(buf, 0, cnt);
    ret = copy_to_user(buf, databuf, cnt);

    dma_free_coherent(&hello_pci_info.pdev->dev, 4096, databuf, dma_handle_addr);

    return ret;
}

/* device file operations function */
static struct file_operations hello_pcie_fops = {
    .owner      = THIS_MODULE,
    .open       = hello_pcie_open,
    .release    = hello_pcie_close,
    .read       = hello_pcie_read,
    .write      = hello_pcie_write,
};


static int hello_pcie_probe(struct pci_dev *pdev, const struct pci_device_id *id)
{
    int bar = 0;
    int ret;
    resource_size_t len;

    ret = pci_enable_device(pdev);
    if(ret) {
        return ret;
    }
    pci_set_master(pdev);

    if (!pci_set_dma_mask(pdev, DMA_BIT_MASK(28))) 
    {
        pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(28));
        dev_info(&pdev->dev, "using a 28-bit dma mask\n");
    } 
    else 
    {
        dev_info(&pdev->dev, "unable to use 28-bit dma mask\n");
        return -1;
    }
    
    len = pci_resource_len(pdev, bar);
    hello_pci_info.address_bar0 = pci_iomap(pdev, bar, len);
    hello_pci_info.pdev = pdev;
    
    // register interrupt
    ret = request_irq(pdev->irq, hello_pci_irq_handler, IRQF_SHARED, "hello_pci", &hello_pci_info);
    if(ret) {
        printk("request IRQ failed.\n");
        return ret;
    }
    // enable irq for finishing factorial computation
    *((uint32_t *)(hello_pci_info.address_bar0 + 0x20)) = 0x80;
    
    return 0;
}

static void hello_pcie_remove(struct pci_dev *pdev)
{
    // disable irq for finishing factorial computation
    *((uint32_t *)(hello_pci_info.address_bar0 + 0x20)) = 0x01;
    
    free_irq(pdev->irq, &hello_pci_info);
    
    pci_iounmap(pdev, hello_pci_info.address_bar0);
    
    pci_disable_device(pdev);
}


static struct pci_driver hello_pci_driver = {
    .name       = "hello_pcie",
    .id_table   = ids,
    .probe      = hello_pcie_probe,
    .remove     = hello_pcie_remove,
};

static int __init hello_pci_init(void)
{
    int ret = pci_register_driver(&hello_pci_driver);

    if(hello_pci_info.pdev == NULL){
        printk("hello_pci: probe pcie device failed!\n");
        return ret;
    }

    /* 1、Request device number */
    ret = alloc_chrdev_region(&hello_pci_info.dev_id, 0, 1, "hello_pcie");
    
    /* 2、Initial char_dev */
    hello_pci_info.char_dev.owner = THIS_MODULE;
    cdev_init(&hello_pci_info.char_dev, &hello_pcie_fops);
    
    /* 3、add char_dev */
    cdev_add(&hello_pci_info.char_dev, hello_pci_info.dev_id, 1);

    /* 4、create class */
    hello_pci_info.class = class_create(THIS_MODULE, "hello_pcie");
    if (IS_ERR(hello_pci_info.class)) {
        return PTR_ERR(hello_pci_info.class);
    }

    /* 5、create device */
    hello_pci_info.device = device_create(hello_pci_info.class, NULL, hello_pci_info.dev_id, NULL, "hello_pcie");
    if (IS_ERR(hello_pci_info.device)) {
        return PTR_ERR(hello_pci_info.device);
    }
    
    return ret;
}

static void __exit hello_pci_exit(void)
{
    if(hello_pci_info.pdev != NULL) {
        cdev_del(&hello_pci_info.char_dev);                     /* del cdev */
        unregister_chrdev_region(hello_pci_info.dev_id, 1);     /* unregister device number */

        device_destroy(hello_pci_info.class, hello_pci_info.dev_id);
        class_destroy(hello_pci_info.class);
    }
    
    pci_unregister_driver(&hello_pci_driver);
}


module_init(hello_pci_init);
module_exit(hello_pci_exit);
MODULE_LICENSE("GPL");
MODULE_INFO(intree, "Y");

注意其中的 pci_set_dma_mask和pci_set_consistent_dma_mask就是为了适应28bit的DMA地址做的适配。

四、编写用户程序

编写用户测试程序testapp.c如下:

c 复制代码 
#include "stdio.h"
#include "stdint.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"

#define BUFFER_LENGTH 128

int main(int argc, char *argv[])
{
    int fd, retvalue;
    char *filename = "/dev/hello_pcie";
    unsigned char *write_buf = malloc(BUFFER_LENGTH);
    unsigned char *read_buf = malloc(BUFFER_LENGTH);
    
    /* 打开驱动设备文件 */
    fd = open(filename, O_RDWR);
    if(fd < 0){
        printf("file %s open failed!\n", filename);
        return -1;
    }

    for(int i = 0;i < BUFFER_LENGTH;i++)
    {
        write_buf[i] = i;
    }

    /* 向/dev/hello_pcie文件写入数据 */
    retvalue = write(fd, write_buf, BUFFER_LENGTH);
    if(retvalue < 0){
        printf("Write %s Failed!\n", filename);
        close(fd);
        return -1;
    }
    printf("write success, data: 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x\n", write_buf[0], write_buf[1], write_buf[2], write_buf[3], write_buf[4], write_buf[5], write_buf[6], write_buf[7]);

    retvalue = read(fd, read_buf, BUFFER_LENGTH);
    if(retvalue < 0){
        printf("Read %s Failed!\n", filename);
        close(fd);
        return -1;
    }
    printf("read success, data: 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x, 0x%0x\n", read_buf[0], read_buf[1], read_buf[2], read_buf[3], read_buf[4], read_buf[5], read_buf[6], read_buf[7]);

    retvalue = close(fd); /* 关闭文件 */
    if(retvalue < 0){
        printf("file %s close failed!\r\n", filename);
        return -1;
    }

    return 0;
}

五、运行测试

编译加载驱动，

使用如下命令编译测试程序：

bash 复制代码 
gcc testapp.c

然后运行测试程序，可以看到符合预期结果

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