DMA理論：https://blog.csdn.net/yizhiniu_xuyw/article/details/113809126

驅動層代碼：

#include <linux/kernel.h> #include <linux/fs.h> #include <linux/init.h> #include <linux/module.h> #include <linux/device.h>? #include <linux/cdev.h>? #include <linux/dmaengine.h> #include <linux/wait.h> #include <linux/string.h> #include <linux/dma-mapping.h> #include <linux/slab.h> #include <linux/jiffies.h>#define DEBUG_PRINT printk#define MEMCPY_NO_DMA 0 #define MEMCPY_DMA ? ?1 #define BUFF_SIZE ? ? (512*1024)struct cdev my_cdev; static int major_ret; static struct class *pdma_class; static struct device *pdma_device;static dma_addr_t *src = NULL; static dma_addr_t src_phys ; static dma_addr_t *dst = NULL; static dma_addr_t dst_phys ;static volatile int dma_finished = 0; static DECLARE_WAIT_QUEUE_HEAD(wq);static void do_memcpy_no_dma(void) {unsigned long t1 , t2,diff,msec;int i ;t1 ?= jiffies;for(i = 0;i < 1000;i++){memcpy(dst,src,BUFF_SIZE);?? ?}t2 = jiffies;diff = (long)t2 - (long)t1;msec = diff *1000/HZ;DEBUG_PRINT("used:%ld ms\n",msec);}static void tx_callback(void *dma_async_param) {//DEBUG_PRINT("callback here\n");dma_finished = 1;wake_up_interruptible(&wq); }static int do_memcpy_with_dma(void) {struct dma_chan *chan = NULL;dma_cap_mask_t mask;struct dma_async_tx_descriptor *tx = NULL;dma_cookie_t dma_cookie;memset(src,0xAA,BUFF_SIZE);memset(dst,0x55,BUFF_SIZE);?? ?dma_cap_zero(mask);dma_cap_set(DMA_MEMCPY, mask);chan = dma_request_channel(mask, NULL, NULL);if(NULL == chan ){printk("err:%s:%d\n",__FILE__,__LINE__);?? ??? ?return -1;}unsigned long t1 , t2,diff,msec;int i ;t1 ?= jiffies;for(i=0;i<1000;i++){dma_finished = 0;//tx = dmaengine_prep_dma_cyclic(chan, src_phys, BUFF_SIZE, 1024, DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT|DMA_CTRL_ACK);tx = dmaengine_prep_dma_memcpy(chan, dst_phys, src_phys, BUFF_SIZE, DMA_PREP_INTERRUPT|DMA_CTRL_ACK);if(NULL == tx){printk("err:%s:%d\n",__FILE__,__LINE__);?? ?dma_release_channel(chan);return -1;}tx->callback = tx_callback;dma_cookie = dmaengine_submit(tx);if (dma_submit_error(dma_cookie)){printk("Failed to do DMA tx_submit");}dma_async_issue_pending(chan);?? ?wait_event_interruptible(wq, dma_finished);}t2 ?= jiffies;diff = (long)t2 - (long)t1;msec = diff *1000/HZ;DEBUG_PRINT("used:%ld ms\n",msec);printk("ok !\n");if(memcmp(src, dst, BUFF_SIZE) == 0){printk("memcpy succ !\n");}else{printk("memcpy failed !\n");int i = 0;for(i=0;i<8;i++){printk("%x | %x\n",src[i],dst[i]);}}?? ?dma_release_channel(chan);}static long dma_ioctl(struct file *file, unsigned int cmd, unsigned long data) {switch (cmd){case MEMCPY_NO_DMA:do_memcpy_no_dma();break;case MEMCPY_DMA:do_memcpy_with_dma();break;}return 0; }static const struct file_operations fops = {.owner = THIS_MODULE,.unlocked_ioctl = dma_ioctl, };static int __init dma_init(void) {dev_t devno = 0;alloc_chrdev_region(&devno, 0, 1, "my-dma");major_ret = MAJOR(devno);cdev_init(&my_cdev, &fops);cdev_add(&my_cdev, devno, 1);pdma_class = class_create(THIS_MODULE, "my-dma-class");pdma_device = device_create(pdma_class, NULL, MKDEV(major_ret,0), NULL, "my-dma");src = dma_alloc_coherent(NULL, BUFF_SIZE, &src_phys, GFP_KERNEL);if(NULL == src){printk("err:%s:%d\n",__FILE__,__LINE__);goto _FAILED_ALLOC_SRC;}dst = dma_alloc_coherent(NULL, BUFF_SIZE, &dst_phys, GFP_KERNEL);?? ?if(NULL == dst){?? ??? ?printk("err:%s:%d\n",__FILE__,__LINE__);goto _FAILED_ALLOC_DST;}return 0; _FAILED_ALLOC_DST:?? ?dma_free_coherent(NULL, BUFF_SIZE, src, src_phys); _FAILED_ALLOC_SRC:device_destroy(pdma_class, MKDEV(major_ret,0));?class_destroy(pdma_class);?? ?cdev_del(&my_cdev);unregister_chrdev_region(MKDEV(major_ret, 0), 1);return -1;}static void __exit dma_exit(void) {?? ?//printk("hello dma openwrt exit\n");device_destroy(pdma_class, MKDEV(major_ret,0));?? ?class_destroy(pdma_class);dev_t devno = MKDEV(major_ret, 0);cdev_del(&my_cdev);unregister_chrdev_region(devno, 1);?? ?dma_free_coherent(NULL, BUFF_SIZE, src, src_phys);dma_free_coherent(NULL, BUFF_SIZE, dst, dst_phys);?? ?}module_init(dma_init); module_exit(dma_exit);MODULE_AUTHOR("hello world"); MODULE_DESCRIPTION("dma driver"); MODULE_LICENSE("GPL"); //MODULE_ALIAS("platform:" DRV_NAME);

應用層測試代碼：

#include <stdint.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <getopt.h> #include <fcntl.h> #include <sys/ioctl.h> #include <linux/types.h>#define MEMCPY_NO_DMA 0 #define MEMCPY_DMA ? ?1void print_usage(char *argv) {printf("usge:\n");printf("%s <nodma|dma> \n"); }int main(int argc ,char **argv) {if(argc < 2){print_usage(argv[0]);return -1;}int fd = open("/dev/my-dma",O_RDWR);if(fd < 0){printf("open /dev/my-dma failed!\n");return -1;}if(strcmp("dma", argv[1]) == 0){ioctl(fd,MEMCPY_DMA);}else{ioctl(fd,MEMCPY_NO_DMA);}close(fd);}

測試結果：（H3 平臺）
DMA 比 memcpy 快一倍！

疑問：

tx = dmaengine_prep_dma_memcpy(chan, dst_phys, src_phys, BUFF_SIZE, DMA_PREP_INTERRUPT|DMA_CTRL_ACK);

這里的 tx 沒有看到 在哪 free 的，是否會內存泄漏？
答：不會，傳輸完成后由中斷處理函數自動釋放內存。

代碼跟蹤：

dmaengine_prep_dma_memcpysun6i_dma_prep_dma_memcpyreturn vchan_tx_prep(&vchan->vc, &txd->vd, flags);list_add_tail(&vd->node, &vc->desc_allocated);

? 先看 struct virt_dma_chan

struct virt_dma_chan {struct dma_chan?? ?chan;struct tasklet_struct task;void (*desc_free)(struct virt_dma_desc *);spinlock_t lock;/* protected by vc.lock */struct list_head desc_allocated;struct list_head desc_submitted;struct list_head desc_issued;struct list_head desc_completed;struct virt_dma_desc *cyclic; };

里面包含了void (*desc_free)(struct virt_dma_desc *); desc_free 函數。
來看一下desc_free 函數在哪被調用？

sun6i_dma_probevchan->vc.desc_free = sun6i_dma_free_desc;vchan_inittasklet_init(&vc->task, vchan_complete, (unsigned long)vc)vchan_completelist_for_each_entry_safe(vd, _vd, &head, node) {dmaengine_desc_get_callback(&vd->tx, &cb);list_del(&vd->node);if (dmaengine_desc_test_reuse(&vd->tx))list_add(&vd->node, &vc->desc_allocated);elsevc->desc_free(vd);?? ??? ? ? ? //最終調用 sun6i_dma_free_descdmaengine_desc_callback_invoke(&cb, NULL);}ret = devm_request_irq(&pdev->dev, sdc->irq, sun6i_dma_interrupt, 0,dev_name(&pdev->dev), sdc);sun6i_dma_interrupt ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? // dma 中斷處理函數vchan_cyclic_callback?tasklet_schedule(&vc->task) ? ? ? ? ? ? ?//這里之后調用 vchan_completestatic void sun6i_dma_free_desc(struct virt_dma_desc *vd) {struct sun6i_desc *txd = to_sun6i_desc(&vd->tx);struct sun6i_dma_dev *sdev = to_sun6i_dma_dev(vd->tx.chan->device);struct sun6i_dma_lli *v_lli, *v_next;dma_addr_t p_lli, p_next;if (unlikely(!txd))return;p_lli = txd->p_lli;v_lli = txd->v_lli;while (v_lli) {v_next = v_lli->v_lli_next;p_next = v_lli->p_lli_next;dma_pool_free(sdev->pool, v_lli, p_lli);v_lli = v_next;p_lli = p_next;}kfree(txd); ? ?//釋放內存 }

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