linux下DMA驱动测试代码

DMA传输可以是内存到内存、内存到外设和外设到内存。这里的代码通过dma驱动实现了内存到内存的数据传输。

/*
Function description:When we call dmatest_read(),it will transmit src memory data
to dst memory,then print dst memory data by dma_callback_func(void) function.
*/
#include<linux/module.h>
#include<linux/init.h>
#include<linux/fs.h>
#include<linux/sched.h>

#include<linux/device.h>
#include<linux/string.h>
#include<linux/errno.h>

#include<linux/types.h>
#include<linux/slab.h>
#include<linux/dmaengine.h>
#include<linux/dma-mapping.h>

#include<asm/uaccess.h>

#define DEVICE_NAME "dma_test"
unsigned char dmatest_major;
static struct class *dmatest_class;

struct dma_chan *chan;
 //bus address
dma_addr_t dma_src;
dma_addr_t dma_dst;
//virtual address
char *src = NULL;
char *dst = NULL ;
struct dma_device *dev;
struct dma_async_tx_descriptor *tx = NULL;
enum dma_ctrl_flags flags;
dma_cookie_t cookie;

//When dma transfer finished,this function will be called.
void dma_callback_func(void)
{
	int i;
	for (i = 0; i < 512; i++){
		printk(KERN_INFO "%c",dst[i]);
	}
}

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

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

static ssize_t dmatest_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
	int ret = 0;
	//alloc a desc,and set dst_addr,src_addr,data_size.
	tx = dev->device_prep_dma_memcpy(chan, dma_dst, dma_src, 512, flags);
	if (!tx){
		printk(KERN_INFO "Failed to prepare DMA memcpy");
	}
	
	tx->callback = dma_callback_func;//set call back function
	tx->callback_param = NULL;
	cookie = tx->tx_submit(tx); //submit the desc
	if (dma_submit_error(cookie)){
		printk(KERN_INFO "Failed to do DMA tx_submit");
	}
	
	dma_async_issue_pending(chan);//begin dma transfer
	
	return ret;
}

static ssize_t dmatest_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
{
	int ret = 0;
	return ret;
}

static const struct file_operations dmatest_fops = {
	.owner = THIS_MODULE,
	.read = dmatest_read,
	.write = dmatest_write,
	.open = dmatest_open,
	.release = dmatest_release,
};

int dmatest_init(void)
{
	int i;
	dma_cap_mask_t mask;
	
	//the first parameter 0 means allocate major device number automatically
	dmatest_major = register_chrdev(0,DEVICE_NAME,&dmatest_fops);
	if (dmatest_major < 0) 
		return dmatest_major;
	//create a dmatest class
	dmatest_class = class_create(THIS_MODULE,DEVICE_NAME);
	if (IS_ERR(dmatest_class))
		return -1;
	//create a dmatest device from this class
	device_create(dmatest_class,NULL,MKDEV(dmatest_major,0),NULL,DEVICE_NAME);


	//alloc 512B src memory and dst memory
	src = dma_alloc_coherent(NULL, 512, &dma_src, GFP_KERNEL);
	printk(KERN_INFO "src = 0x%x, dma_src = 0x%x\n",src, dma_src);
	
	dst = dma_alloc_coherent(NULL, 512, &dma_dst, GFP_KERNEL);
	printk(KERN_INFO "dst = 0x%x, dma_dst = 0x%x\n",dst, dma_dst);
		
	for (i = 0; i < 512; i++){
		*(src + i) = 'a';
	}

	dma_cap_zero(mask);
	dma_cap_set(DMA_MEMCPY, mask);//direction:memory to memory
	chan = dma_request_channel(mask,NULL,NULL); //request a dma channel
	printk(KERN_INFO "dma channel id = %d\n",chan->chan_id);
	
	flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
	dev = chan->device;
	
	return 0;
}

void dmatest_exit(void)
{
	unregister_chrdev(dmatest_major,DEVICE_NAME);//release major device number
	device_destroy(dmatest_class,MKDEV(dmatest_major,0));//destroy globalmem device
	class_destroy(dmatest_class);//destroy globalmem class
	
	//free memory and dma channel
	dma_free_coherent(NULL, 512, src, &dma_src);
	dma_free_coherent(NULL, 512, dst, &dma_dst);
	
	dma_release_channel(chan);
}

module_init(dmatest_init);
module_exit(dmatest_exit);

MODULE_LICENSE("GPL");