DMA的demo

最新推荐文章于 2023-12-14 12:24:48 发布

wh8_2011

最新推荐文章于 2023-12-14 12:24:48 发布

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分类专栏： linux-DMA 文章标签： linux dma

本文链接：https://blog.youkuaiyun.com/wh8_2011/article/details/52558190

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本文通过一个具体的示例，详细介绍了在Linux操作系统中如何使用DMA（直接内存访问）技术，探讨了DMA的工作原理及其在提升数据传输效率中的关键作用。

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DMA的demo

static void fsl_dma_test_callback(void *dma_async_param)
{
   struct completion *cmp = dma_async_param;
   printk( KERN_ERR "dma transfer done, end=%lu\n", jiffies );
   complete(cmp);
}

static int fsl_dma_self_test(struct dma_chan *chan)
{
   int i;
   u8 *src;
   u8 *dest;
   struct dma_device *dma = chan->device;
   struct device *dev = dma->dev;
   struct dma_chan* dma_chan = chan;
   struct dma_async_tx_descriptor *tx;
   dma_addr_t dma_dest, dma_src;
   dma_cookie_t cookie;
   int err = 0;
   struct completion cmp;
   unsigned long tmo;
   unsigned long flags;
   u32 test_size = 1024*1024*4u;

   src = kzalloc(sizeof(u8) * test_size, GFP_KERNEL);
   if (!src)
       return -ENOMEM;
   dest = kzalloc(sizeof(u8) * test_size, GFP_KERNEL);
   if (!dest) {
       kfree(src);
       return -ENOMEM;
   }

   /* Fill in src buffer */
   for (i = 0; i < test_size; i++)
       src[i] = (u8)i;

   /* Start copy, using first DMA channel */
   dma_src = dma_map_single(dev, src, test_size, DMA_TO_DEVICE);
   dma_dest = dma_map_single(dev, dest, test_size, DMA_FROM_DEVICE);
   flags = DMA_COMPL_SRC_UNMAP_SINGLE | DMA_COMPL_DEST_UNMAP_SINGLE |
       DMA_PREP_INTERRUPT;

   printk( KERN_ERR "try to dma copy %d bytes: 0x%08x-->0x%08x\n", test_size, dma_src,     dma_dest );
   tx = dma->device_prep_dma_memcpy(dma_chan, dma_dest, dma_src,
                          test_size, flags);
   if (!tx) {
       dev_err(dev, "Self-test prep failed, disabling\n");
       err = -ENODEV;
       goto free_resources;
   }

   async_tx_ack(tx);
   init_completion(&cmp);
   tx->callback = fsl_dma_test_callback;
   tx->callback_param = &cmp;
   cookie = tx->tx_submit(tx);
   if (cookie < 0) {
       dev_err(dev, "Self-test setup failed, disabling\n");
       err = -ENODEV;
       goto free_resources;
   }

   printk( KERN_ERR "begin dma transfer: %d bytes, start=%lu\n", test_size, jiffies );
   dma->device_issue_pending(dma_chan);

   tmo = wait_for_completion_timeout(&cmp, msecs_to_jiffies(3000));

   if (tmo == 0 ||
       dma->device_tx_status(dma_chan, cookie, NULL)
                   != DMA_SUCCESS) {
       dev_err(dev, "Self-test copy timed out, disabling\n");
       err = -ENODEV;
       goto free_resources;
   }
   if (memcmp(src, dest, test_size)) {
       dev_err(dev, "Self-test copy failed compare, disabling\n");
       err = -ENODEV;
       goto free_resources;
   }

free_resources:
    dma->device_free_chan_resources(dma_chan);
    kfree(src);
   kfree(dest);
   return err;
}



static int __init test_init(void)
{
    struct dma_chan *dc = dma_find_channel(DMA_MEMCPY);
    if (dc) {
        printk(" ------- get channel ----\n");
        fsl_dma_self_test(dc);
    }
    printk(" ------- init time ----\n");
    return 0;
}

static void __exit test_exit(void)
{
    printk("-------- test exit over ----------\n");
    return;
}

MODULE_LICENSE("GPL");

module_init(test_init);
module_exit(test_exit);